Processing, Characteristics and Composition of Umqombothi (a South African Traditional Beer)

: Traditional beers, such as palm wine, kombucha and others, are notable beverages consumed all over the globe. Such beverages historically contribute to food security on a global scale. Umqombothi is a South African traditional beer nutritionally packed with minerals, amino acids, B-group vitamins and much-needed calories. As a result, the production and consumption of this traditional beverage has been an integral part of South African’s social, economic and cultural prosperity. Unfortunately, di ﬃ culties in bioprocessing operations have limited its availability to household and small-scale production. It is at these micro-production scales that poor hygiene practices and the use of hazardous additives and contaminated raw materials continue to increase, posing serious health risks to the unassuming consumer. This study provides an overview of the processing steps and underlying techniques involved in the production of umqombothi , while highlighting the challenges as well as future developments needed to further improve its quality and global competitiveness with other alcoholic products.


Introduction
The production of cereal-based beers in Africa date back to 3500 BC [1][2][3]. Historians believe that the domestication of cereal crops in North Africa, between 4650 and 4350 BC, catalysed interests in beer brewing [4]. Across the continent, millet, maize and sorghum beers are produced in different regions based on the type of crop widely distributed [5,6]. Although sorghum accounts for only 23% of the farmed land area, sorghum beers, usually termed "African opaque beers", are amongst the most popular types of beer in many countries such as South Africa, Nigeria, Ghana, Togo and Zimbabwe [1][2][3]5,7].
Umqombothi is an IsiZulu term describing a sorghum-based beer with an opaque pinkish colour, creamy constituency and sour aroma ( Figure 1) [2,10]. The consumption of umqombothi is common in Regardless of the health benefits and affordability, brewing umqombothi has not been formally standardised, especially on a household level [1,8]. This may be because the old-age method of making traditional beer requires the knowledge, skill and expertise of the local people, usually African elderly women who use diverse self-taught beer preparation methods [1,2,12]. The lack of standard procedures and guidelines lead to day-to-day fermentation variances which subsequently result in inconsistent taste, body and texture of the beer [3,8]. On a commercial scale, the production is limited to a few local products [8]. Brewers report that the production activities and the monetary reward are often disproportionately unattractive to investors interested in product development and commercialisation [2,13].
Concerns over general hygiene practices, toxic substances, the behaviour, knowledge and attitude of informal brewers and the beer's microbial composition have equally been raised by South African authorities [2,12]. Contaminated beer has led authorities to close down local pubs (shebeens) and publicly dispose home-brewed beer to discourage its consumption [2,12]. A study by Lues [2] found that "50% of brewers washed the containers when visibly dirty, while 45% washed them after use." A similar finding relating to washing of hands found that 45% of brewers washed their hands only after visiting the bathroom, while 55% washed their hands only when "really" dirty [12]. Unwashed utensils and unwashed vessels largely contribute to the proliferation of spoilage microorganism and unwanted contaminants [2,10,12,14].
In some instances, brewers have added hazardous "ingredients" such as battery ash, battery acid and methylated spirits to make umqombothi more concentrated or to superstitiously attract more customers [2,12,15]. Such breaches in household production of the beer are not uncommon, especially where the demand may dictate the production process. During periods of high demand, the cooking step may be skipped and the fermentation process may be shorted and/or halted altogether to satisfy Regardless of the health benefits and affordability, brewing umqombothi has not been formally standardised, especially on a household level [1,8]. This may be because the old-age method of making traditional beer requires the knowledge, skill and expertise of the local people, usually African elderly women who use diverse self-taught beer preparation methods [1,2,12]. The lack of standard procedures and guidelines lead to day-to-day fermentation variances which subsequently result in inconsistent taste, body and texture of the beer [3,8]. On a commercial scale, the production is limited to a few local products [8]. Brewers report that the production activities and the monetary reward are often disproportionately unattractive to investors interested in product development and commercialisation [2,13].
Concerns over general hygiene practices, toxic substances, the behaviour, knowledge and attitude of informal brewers and the beer's microbial composition have equally been raised by South African authorities [2,12]. Contaminated beer has led authorities to close down local pubs (shebeens) and publicly dispose home-brewed beer to discourage its consumption [2,12]. A study by Lues [2] found that "50% of brewers washed the containers when visibly dirty, while 45% washed them after use." A similar finding relating to washing of hands found that 45% of brewers washed their hands only after visiting the bathroom, while 55% washed their hands only when "really" dirty [12]. Unwashed utensils and unwashed vessels largely contribute to the proliferation of spoilage microorganism and unwanted contaminants [2,10,12,14].
In some instances, brewers have added hazardous "ingredients" such as battery ash, battery acid and methylated spirits to make umqombothi more concentrated or to superstitiously attract more customers [2,12,15]. Such breaches in household production of the beer are not uncommon, especially where the demand may dictate the production process. During periods of high demand, the cooking step may be skipped and the fermentation process may be shorted and/or halted altogether to  [2,10,12]. As a result, the final beer product is often less nutritious, tasty and safe for consumers [2,3,8,12]. These factors, together with low ethanol content, shorter shelf life and organoleptic variations, have rendered traditional African beer to appear less attractive than barley-brewed western beers [8,16].
The challenges around general quality and the health hazards linked to production and consumption of traditional beer will therefore continue to persist unless adequate efforts are put in place to improve the process and ensure consistency in its composition. This review provides an overview of umqombothi production as well as its composition. Within the scope of the production, the underlying science governing each of the processing steps are covered. Challenges of umqombothi processing were discussed as well as an appraisal from available literature and information regarding its microbiota and beneficial properties. Attempts at improving its quality were also highlighted with a section of pertinent areas for innovative approaches requiring further development.

The Socioeconomic, Cultural and Spiritual Significance of Umqombothi
Umqombothi is an affordable beverage in low-income households, especially rural areas where poverty and malnutrition are a constant concern [2,12,13]. Low-income populations in semi-urban areas also benefit from consuming this low-cost beer [2,13]. As a result, daily consumption increases as brewers in rural and semi-urban areas prepare and sell umqombothi to make a living [10,13]. High financial gains by brewers can thus be expected because of increased consumption and customer demand [1,2,12]. In Dikgale, Limpopo province, South Africa, an average of 1.3 L daily consumption of umqombothi per person is reported [13].
Brewers in the Kimberly, in the Northern Cape Province of South Africa, reported an average monthly income of USD 105, depending on customer availability. Conversely, brewers in Bushbuckridge, South Africa, reported earning as little as USD 8 and as much as USD 211 per month [2,17]. In the past, umqombothi was purposely brewed for social activities with minimal regard for deriving income [12]. Presently, only 25% is attributed to brewing for social and cultural activities [2]. Umqombothi is always a choice of drink during cooperative work, weddings and the handing over of a dowry, circumcision and initiation school graduation celebrations, births and funerals, communication with ancestors or spirits, praying for rain and social meetings [1,2,8,12,13].

Processing Steps Involved in Brewing Practices of Umqombothi
The ingredients used in the making of umqombothi are malted cereals (wheat, maize, sorghum), sugar and brown bread (optional), which are broken down by wild yeasts and bacteria to produce an alcoholic end product through a stepwise process, as depicted in Figure 2. On a household level, umqombothi is generally prepared by self-taught elderly women by hand-mixing 1 kg wheat malt, 1.4 kg brown bread (optional), 1 kg sorghum malt, 1 kg maize meal, 10 g wet (compressed) yeast, and 1 kg brown sugar in an iron-cast pot or plastic bucket filled with 20 L lukewarm water [1,2,12,13]. Pre-weighed packets of these ingredients are commercially available under different brand names, but these ingredients (if not pre-packed) are seldom weighed [12,18,19]. The elderly women and sometimes men, use previous experience and basically "gauge" the weights by hands, cups or bowls. Thus, like the production of other sorghum beers, the production of umqombothi lacks measurement precision necessary for satisfactory quality control [16]. Irrespective of the ingredient source, the mixing process aids the uniform distribution of the raw materials and is usually done in an earthen vessel or iron-cast pot [2,12,13].
Formerly, the cooking and fermentation processes occurred solely in iron-cast pots [13]. Ironcast pots and non-galvanised iron vessels, however, are still vessels of choice for the cooking stage of the process [1,2,13,20]. The beer is then poured into a large plastic drum known as a gogogo for sharing with friends and family [2,12,13,21]. Modern brewers use cheap, easy to clean and rust-resistant twenty litres buckets to store the indigenous beer as opposed to traditional clay pots [2,12]. Traditionally, umqombothi was served in clay beer-drinking vessel known as ukhamba ( Figure 2). During the fermentation process, the fermenting microorganisms produce substances that give umqombothi its characteristics pH, aroma, consistency and unique sensory properties. As observed in Ideally, a previously used iron-cast pot or plastic bucket (sometimes plastic drum) is used to soak the mixed ingredients overnight to foster spontaneous wild-yeasts fermentation, followed by cooking to break up the yeast cells to release locked-up nutrients and gelatinise the starch [1,2,12,13]. While the cooking step is vital, prolonged cooking periods could reduce the nutritional value of the beverage and significantly reduce available sugars for fermentation. Subsequent to this is cooling, conducted in a plastic bucket or iron-cast pot which is then tightly covered overnight to facilitate secondary fermentation, predominately performed by lactic acid bacteria (LAB) [1,2,8,12,14]. During winter time, the container may be covered with a blanket or a fire may be lit to provide a warm fermentation environment favourable for the fermentation microbes. At present, the fermentation of umqombothi is allowed to proceed in plastic drums or iron pots [13]. A four-day summary of the traditional method of making umqombothi is shown in Table 1. Mix ingredients together in a 20 L bucket. Place lid on top without sealing it and allow fermentation to proceeded overnight in a warm area or covered with a blanket and/or placed next to a fire (in winter times).

-Large container, iron-cast pot
Resuspended ingredients by stirring. Fill a large pot with between 1/5 and 3/5 of water and heat to boiling point. Add the fermented mixture to the boiling water until a slurry is formed. The cooked slurry is left on a large container and allowed to cool throughout the rest of the day and overnight.

3
Wheat malt and previously cooked slurry Blanket (optional) A sufficient amount (1-3 kg) of wheat malt is added to the porridge. The mixture is gently stirred and allowed to ferment overnight in a warm area or covered with a blanket and/or placed next to a fire (in winter times).

-
Woven sieve (ivovo), a traditional beer-drinking vessel (ukhamba) The fermented mixture is stirred and the beer strained using a woven sieve (ivovo) to remove unwanted suspended solids. The desired beer can then be served on ukhamba and stored in large plastic drum (gogogo).
Formerly, the cooking and fermentation processes occurred solely in iron-cast pots [13]. Iron-cast pots and non-galvanised iron vessels, however, are still vessels of choice for the cooking stage of the process [1,2,13,20]. The beer is then poured into a large plastic drum known as a gogogo for sharing with friends and family [2,12,13,21]. Modern brewers use cheap, easy to clean and rust-resistant twenty litres buckets to store the indigenous beer as opposed to traditional clay pots [2,12]. Traditionally, umqombothi was served in clay beer-drinking vessel known as ukhamba ( Figure 2).
During the fermentation process, the fermenting microorganisms produce substances that give umqombothi its characteristics pH, aroma, consistency and unique sensory properties. As observed in the literature, different fermentation regimes are used for umqombothi (Table 2), and the differences which might have an effect on the overall composition of the product were reported [1,[8][9][10]12,14,16,[21][22][23][24].

Early Industrialisation Attempts for Umqombothi Processing
Early industrialisation attempts were made for processing umqombothi in South Africa, with the first commercialisation of umqombothi starting in 1908 after the municipal monopoly by town authorities was authorised by Natal legislative assembly in the British colony [25]. Unfortunately, political unrest of the 1970s, the introduction and superior marketing of clear malt beers by South African Breweries (SAB), and consumer repulsion of sorghum beer due to its associations with apartheid government schemes led to the decommercialisation of umqombothi from 1980 [25]. To keep up with new consumption trends, private brewing companies such as Ukhamba Beerworx and United National Breweries are resuscitating the industrialisation of umqombothi [26,27].
For the industrialised processes, mixing, incubation, boiling, cooling, fermentation and filtration constitute the brewing process of traditional beers [2,12]. Although variations in the brand used exist, 10 kg maize meal and 10 kg maize malt are mixed into a 500 L bioreactor [28,29]. To make a paste (or wort), 2.5 kg wheat malt is added to 200 L lukewarm water (35 • C-45 • C) containing 10 kg maize meal and 10 kg maize malt [23,28,29]. To homogenise and make a "porridge", the slurry is boiled for 30 min at 45 • C while gently stirring.
Thereafter, the cooked porridge is cooled to an ambient temperature. An additional 7.5 kg wheat malt is added to the cool porridge and homogenised with gentle stirring [16,[28][29][30]. Fermentation with gentle stirring is then allowed to proceed for 8 h [16,29,31]. Depending on the maturation of the brew, the mixture is allowed to ferment for an additional 8 h at 35 • C [12,23,28,29]. The beer is then filtered to remove unwanted or residual suspended solids, and the final product is recovered as depicted in Figure 3

Composition of Umqombothi and Benefits
The composition (functional qualitative aspects) of any type of beer determines its popularity amongst consumers [3,33]. The nutritional, medicinal and sensory properties of beer give it its desirable qualities [3]. In general, sensory, physical and physicochemical, chemical and biochemical and microbiological evaluation are fundamental subcategories of qualitative aspects in beer brewing [3]. As a result, the composition of beer characterises its main qualities: mouthfeel, aroma, appearance and flavour [33]. The type of raw material used as well as the fermentation process are primarily responsible for these sensory qualities [2,8,14,33]. Unfortunately, qualitative aspects are seldom controlled in traditionally manufactured African beers [34]. In addition, there is scarcity of data describing the nutritional and biochemical composition of local sorghum beers [12,34].

Physicochemical Constituents
Since consumers believe drinking coloured beers is healthy, umqombothi is often brewed from pigmented sorghum varieties [8]. The sorghum and ancillary ingredients used dictate the colour, which varies from pinkish brown to a pale buff [8]. This practice means that umqombothi is opaque and not clear due to suspended solids. Suspended solids (5-7%) are mostly starch residues, dextrins and dietary fibres, which also give the beer its high calories [1,8,12,20,35]. Depending on where and how the beer is brewed, umqombothi has an average pH range of 3 to 4.2, a lactic acid level of 0.26% and a low alcohol content of 2-3.5% v/v [8,12,14].

Composition of Umqombothi and Benefits
The composition (functional qualitative aspects) of any type of beer determines its popularity amongst consumers [3,33]. The nutritional, medicinal and sensory properties of beer give it its desirable qualities [3]. In general, sensory, physical and physicochemical, chemical and biochemical and microbiological evaluation are fundamental subcategories of qualitative aspects in beer brewing [3]. As a result, the composition of beer characterises its main qualities: mouthfeel, aroma, appearance and flavour [33]. The type of raw material used as well as the fermentation process are primarily responsible for these sensory qualities [2,8,14,33]. Unfortunately, qualitative aspects are seldom controlled in traditionally manufactured African beers [34]. In addition, there is scarcity of data describing the nutritional and biochemical composition of local sorghum beers [12,34].

Physicochemical Constituents
Since consumers believe drinking coloured beers is healthy, umqombothi is often brewed from pigmented sorghum varieties [8]. The sorghum and ancillary ingredients used dictate the colour, which varies from pinkish brown to a pale buff [8]. This practice means that umqombothi is opaque and not clear due to suspended solids. Suspended solids (5-7%) are mostly starch residues, dextrins and dietary fibres, which also give the beer its high calories [1,8,12,20,35]. Depending on where and how the beer is brewed, umqombothi has an average pH range of 3 to 4.2, a lactic acid level of 0.26% and a low alcohol content of 2-3.5% v/v [8,12,14].

Composition of Umqombothi and Benefits
The composition (functional qualitative aspects) of any type of beer determines its popularity amongst consumers [3,33]. The nutritional, medicinal and sensory properties of beer give it its desirable qualities [3]. In general, sensory, physical and physicochemical, chemical and biochemical and microbiological evaluation are fundamental subcategories of qualitative aspects in beer brewing [3]. As a result, the composition of beer characterises its main qualities: mouthfeel, aroma, appearance and flavour [33]. The type of raw material used as well as the fermentation process are primarily responsible for these sensory qualities [2,8,14,33]. Unfortunately, qualitative aspects are seldom controlled in traditionally manufactured African beers [34]. In addition, there is scarcity of data describing the nutritional and biochemical composition of local sorghum beers [12,34].

Physicochemical Constituents
Since consumers believe drinking coloured beers is healthy, umqombothi is often brewed from pigmented sorghum varieties [8]. The sorghum and ancillary ingredients used dictate the colour, which varies from pinkish brown to a pale buff [8]. This practice means that umqombothi is opaque and not clear due to suspended solids. Suspended solids (5-7%) are mostly starch residues, dextrins and dietary fibres, which also give the beer its high calories [1,8,12,20,35]. Depending on where and how the beer is brewed, umqombothi has an average pH range of 3 to 4.2, a lactic acid level of 0.26% and a low alcohol content of 2-3.5% v/v [8,12,14].
Typically, umqombothi has a creamy constituency, distinctive sour taste, and fruity odour [1,2,8,10,12,14]. The sour taste is attributed to presence of LAB and formation of organic acids during fermentation [2,12]. The fruity odour may occur as a result of the presence of certain microorganisms, especially Candida species and/or the production of diacetyl from wild-type strains of Saccharomyces species [1,8]. Traditional beers, including umqombothi, have a short shelf life (24 h-72 h) and are thus consumed in an actively fermenting state [1,8,10,14].

Nutritional Content and Health Benefits
Umqombothi is a calorie-rich beverage able to provide 130-394 kJ/100 g (Table 3), making it a great source of energy for millions of African people, especially in poverty-stricken societies [1,8,20]. The raw materials and the fermentation process involved makes umqombothi rich in B-group vitamins including thiamine (B 1 ), riboflavin (B 2 ), niacin (B 3 ), pantothenic acid (B 5 ), pyridoxin (B 6 ), folic acid (B 9 ) and vitamin C (Table 3) [1,2,8,12,14]. These vitamins are responsible for genomic and non-genomic methylation, clearance of homocysteine, the synthesis of numerous neurochemical transmitters (such as dopaminergic and serotonergic neurotransmitters) and signalling molecules, energy production, DNA/RNA synthesis or repair, and cellular function [36,37]. Vitamins are thus fundamental for longevity, good brain function and general health [36,37].
The presence of probiotics and prebiotics (dietary fibres) in umqombothi promotes good gut health, favourable bowel movements and antimicrobial properties [5,43]. LABs are the dominant microorganisms involved in the fermentation of umqombothi and are thus beneficial to the fermentation process and its end product [1,7,8,43]. Rural communities have derived health benefits through the consumption of probiotic rich-fermented beverages such as umqombothi [7,43]. These probiotics are known to administer bactericidal, bacteriostatic and antimicrobial effects and thus improve intestinal microbial balance of the human body [7,43]. In addition, probiotics promote overall health by optimising gut ecology, antagonising pathogens and spoilage bacteria, improving nutrition modulating the body's immune response, and soothing intestinal disorders [43]. van Heerden published two studies in the late 1980s determining the dietary content in sorghum beer strainings and sorghum beers brewed with sorghum adjunct to be 50 g/kg and 1.1 g/L [44,45]. Typical modern-day sorghum beers contain about 14.5 g/100 g of dietary fibre, which is sufficient for the recommended diary intake of 14 g/1000 kcal for children and adults (Table 3) [27,46]. The size of the sorghum grain will dictate the prebiotic content, which can range from 2% to 30%, with smaller grains having a higher proportion of husk [27]. The fermentation of some these dietary fibres can lead to the generation of bioactive compounds such as short-chain fatty acids (SCFAs), which transform the gut's microflora by increasing its biomass [47,48]. As a result, regular consumption of prebiotics reduces risk of developing type-2 diabetes, colon cancer, obesity, haemorrhoids, hypertension, gastroesophageal reflux disease, diverticulitis, coronary heart disease, stroke, and duodenal ulcers [46][47][48]. Diabetic and non-diabetic individuals can benefit from lower serum cholesterol levels, weight loss, glycemia and insulin sensitivity, enhanced immune function, lipid metabolism, food digestion, and fibre-induced mineral bioavailability [46][47][48].
In a time where mineral deficiencies are prevalent, umqombothi can provide significant amounts of magnesium, zinc, manganese, phosphorus and bioavailable iron (Tables 3 and 4) [1,8,14,20]. Sorghum malt, the main ingredient used in today's preparation of the beer, is rich in manganese, zinc, phosphorus, potassium, copper and iron [7,8,45]. In the case where sorghum grains are used, the germination process increases the availability of minerals, as well as essential amino acids [6]. In addition, minerals are made bioavailable through alcoholic fermentation [27]. A study at Dikgale field site and the surrounding villages in Limpopo Province, South Africa showed that the consumption of umqombothi prevented iron deficiency in people at risk [13]. When compared to non-drinkers, Processes 2020, 8, 1451 9 of 21 women of childbearing age who consumed the beer had significantly higher concentrations of transferrin and serum ferritin [20]. To conclude, Mandishona et al. [20] added, "the consumption of traditional beer, rich in iron, protects women against iron deficiency." Generally, these minerals are responsible for cellular regulation and cellular build-up of living cells and can thus aid in fighting mental health disorders such as chronic anxiety and depression [1,[49][50][51][52][53]. In interviewing regular consumers of umqombothi, Ikalafeng [12] recorded, "the consumers advanced reasons such as stress relief and making their lives easier as some of the factors influencing their drinking habits. It became evident that what was originally a traditionally cultural beverage has taken on a new form, that of a psychological intervention".

Microbiota
Household and small-scale industry brewers often employ spontaneous fermentation practices in the production of umqombothi [1,2,10,12,13,54]. Since there is generally no addition of exogenous "starter cultures", lactic acid and alcoholic fermentation are spontaneously carried out by the natural microbial flora present in one of the raw materials, i.e., malted sorghum, malted maize, bread or wheat [1,2,10,12,13,54]. A common and hazardous practice is the use of previously used and unwashed utensils to mix, soak and enable spontaneous fermentation [2,12]. The microcolonies of yeast-bacteria associations as examined by Katongole [14] in biofilm formation on the surface of unwashed pot surfaces revealed a high occurrence of unidentified and potentially harmful yeasts and bacteria.
During the mashing process, where the ingredients are mixed, soaked and left overnight to sour, spontaneous lactic acid fermentation is carried out by wild yeasts and heterofermentative and homofermentative mesophilic LAB, which may pose potential human health risks [1,[54][55][56][57][58][59]. At this stage, lactic acid bacteria are the dominant species [60]. Van Der Walt [54] found Pediococcus damnosus, Lactobacillus delbrueckii, Levilactobacillus brevis, Leuconostoc dextranicum, Lactiplantibacillus plantarum, Leuconostoc mesenteroides and Limosilactobacillus fermentum to be common isolates in mash as introduced by the ingredients used. Furthermore, the author suggests that the predominance of one species or the other will be determined by the souring temperature, leading to differences in the lactic acid flora profiles in the brew. Specifically, seeding the mash with Lactobacillus delbrueckii at 45 • C has the advantage of reducing the hazard of the development of unwanted microbes in the souring mash, reducing the souring time from 12 to 6 h, and producing the laevorotatory isomer of dextrorotatory and racemic lactic acid, which is nutritionally preferable when a highly acidic beverage such as umqombothi is consumed [54].
To achieve diastatic conversion in the traditional method, additional water and malted sorghum are often added to the soured mash to spontaneously facilitate alcoholic fermentation [54]. Yeasts such as Pichia anomala, Kloeckera apiculata, P. fermentans, Saccharomyces cerevisiae, Kluyveromyces marxianus, Candida krusei, Endomycopsis fibuligera and C. tropicalis have been isolated in both the sorghum malted and the beer [54]. Of the three dominant yeasts, C. krusei, K. apiculata and S. cerevisiae, only S. cerevisiae is the significant microorganism due to its superior fermentative ability [54,55]. Industrially, it is common practice to pitch with selected strains of S. cerevisiae to achieve optimum fermentation [54]. There is no doubt that quality of umqombothi can be enhanced, even on small-scale basis, through the use of commercial and/or tailored autochthonous starter cultures, including selected S. cerevisiae, non-Saccharomyces and LAB [56][57][58][59]. In a study where three different strains of S. cerevisiae were used as inoculum for an 8-day fermentation period, a 3-28% loss of fumonisin B 1 (FB 1 ) and a 9-17% loss of fumonisin B 2 (FB 2 ) was observed [60].
The use of "open" and spontaneous fermentation by independent brewers poses the risk of wild microbial contamination and proliferation, directly impacting the safety and sensory quality of umqombothi [12]. Off-flavours are produced when microbes not originally present in the raw materials contaminate the beer [12]. The development of Acetobacter species, in particular, promotes the formation of volatile acid, thereby reducing the keeping value of umqombothi [54]. In an attempt to achieve diastatic conversion, selected non-toxigenic strains belonging to the genera Aspergillus, Penicillium, Mucor, Oospora and Rhizopus can be reintroduced into boiled, sterile porridges [54].
The presence of microorganisms in fermented products make them vital for health and longevity on a global scale [60]. It has thus become necessary to assess the ecosystems in which these microorganisms exist and how they interact to provide safe and quality food products [61]. Yeasts such as Issatchenkia orientalis, K. apiculate and S. cerevisiae and bacteria such as Levilactobacillus brevis, Limosilactobacillus fermentum and Lactiplantibacillus plantarum are health-imparting microbes found in umqombothi [1][2][3]8,10,12,[54][55][56][57][58].
In ascertaining food microbial ecologies in the modern era, next-generation sequencing (NGS) has proven itself to be a superior tool of microbial identification. As a result, microbial communities in their entirety (i.e., starter cultures and food spoilage microorganisms) and their genetic, metabolic and physiochemical impact on a particular food can be studied [61][62][63][64]. Driven by NGS technologies, classical environmental studies and microbial ecology have evolved into a new field of "metagenomics" [65][66][67], with found application in the food safety assessment and correct management of food fermentations [68][69][70][71]. Staley and Sadowsky [67] described metagenomics as the direct genetic analysis of genomes contained within an environmental sample without prior need for cultivating clonal cultures. Metagenomics is a low-cost microbial identification approach able to provide genetic information on potentially novel biocatalysts, evolutionary profiles, genomic linkages between function and phylogeny for uncultured organisms and broad phylogenetic surveys [67].

Safety Challenges with Umqombothi Processing
Under normal circumstances, traditional beer brewing is a complex bioprocess, making commercialising difficult, especially without the application of innovative solutions [1,8,72]. The production of the traditional beer has been known to take up to five days and is only shortened to three days, depending on consumer demand [2,10,14]. However, this reduction in fermentation time has been associated with bitter, tasteless and poor-quality beer [3,8]. In addition, this practice may promote the proliferation of spoilage microorganisms such as Escherichia coli, Rhizopus stolonifer, Penicillium crustosum, Staphylococcus aureus, Aspergillus parasiticus, A. flavus and Fusarium verticillioides [1,10,12,14]. Conversely, essential fermentation microorganisms are destroyed during the process of excessive heating, sieving, and harsh treatments [3,8]. South African authorities have raised concerns about toxic substances, hygiene practices, microbial contamination and unauthorised practices of informal brewers [2,12,14]. In conjunction with the above-mentioned factors, incomplete fermentation, a high percentage of microorganisms and solids, a short shelf-life and organoleptic variations have rendered traditional African beer to appear less attractive than barley-brewed western beers [8,16]. Thus, for traditional beer to be competitive in the global beer market, novel bioprocessing approaches need to implemented [72].
Ikalafeng [12] analysed South African traditional beer samples in marginal urban settlements in the greater Kimberley area of the Northern Cape Province and found that the mean total viable coliforms and Staphylococcus species were both 10 6 CFU/mL and total fungi was 10 7 CFU/mL. In characterising Staphylococci in commercially brewed umqombothi and home-brewed umqombothi, S. homonis, S. epidermidis, S. aureus, S. saprophyticus and S. xylosus were predominant in both beer types [12]. The high total fungal counts may be attributed to a yeast-favourable pH and yeast-favourable raw materials such as sorghum, maize and bread [7,12]. Katongole, [14] observed that the occurrence of moulds decreased by log 1 to non-detectable levels after soaking the sorghum and maize mixture. Faecal contamination, indicated by the high prevalence of total coliforms and Staphylococci, possibly resulted from poor hygiene practices [12]. Similarly, Enterobacteriaceae counts in home-brewed umqombothi increased after mash cooking, which was attributed to handler-prone contamination [14].
As a result of poor farming, handling, processing and storage practices across Africa, home-processed traditional beers are often heavily contaminated with several mycotoxins [73,74]. Sporadic reports covering beers prepared using sorghum, maize or millet from South Africa, Nigeria, Zambia, Kenya and Lesotho have shown the presence of zearalenone, fumonisin and aflatoxins [60,73]. In rural communities of South Africa, the dependency on cereal grains as a source of food security reinforces the dietary pattern and ethnic tradition of consuming cereal-based fermented products such as umqombothi [2,12,13,57,73,74]. Mycotoxin-related health risks are posed as a result of using highly contaminated home-grown maize in subsequent brews [74]. The harvesters separate the maize harvest by appearance (mouldy and non-mouldy), with the mouldy maize often used as an ingredient in umqombothi brewing, as it is believed to impart a desirable taste to the final beer product [60].
In a survey conducted between 2001 and 2004, only 25% of households in Centane (Eastern Cape Province, South Africa) admitted to the practice of using mouldy maize in traditional beer brewing, whereas 50% of households in Bizana (Eastern Cape Province, South Africa) reportedly used mouldy maize in traditional beer brewing [60]. In ascertaining fumonisin exposure estimation in umqombothi, calculations based on South African commercial beer consumption data were used due to the lack of consumption data for home-brewed beer [73]. The mean total fumonisins in the beer were found to be 0.2 to 1.0 µg/kg body weight/day and 12-59 µg/person/day [73]. For consumers drinking the beer 2-7 days a week, their fumonisin exposure was 6 times (12.0 µg/kg body weight) higher than provisional maximum tolerable daily intake of 2 µg/kg body weight/day set by the Joint FAO/WHO Expert Committee on Food Additives [73].
An investigation of the mycobiota and co-occurrence of mycotoxins in umqombothi by Adekoya [7] revealed a mean fungal load of 3.66 × 10 5 CFU (colony-forming unit)/mL present in the predominant fungal genera (Phoma, Aspergillus, Saccharomyces and Penicillium), with Aspergillus flavus having the highest incidence (26%). Furthermore, the study raised concerns about a typical South African's mycotoxin exposure being above the maximum tolerable daily intake of 2 µg/kg body weight/day as established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) [7,12]. An average 60 kg adult consuming between one and six litres of umqombothi a day is exposed to an estimated 2.20-13.20 µg/kg body weight/day exposure of FB 1 and FB 2 [7]. Deoxynivalenol (found in 84% of the samples), enniatin B (found in 75% of the samples) and FB 1 (found in 53% of the samples) are associated with cytotoxicity, carcinogenicity, neural tube defects and hepatotoxicity, as these mycotoxins are highly reactive in humans and animals [7,12,14].
In Centane, Eastern Cape Province, South Africa, the prevalence of fumonisins, especially from cereal grains (i.e., maize, sorghum), has been associated with high rates of oesophageal cancer [60,74]. Upon quantitative investigation of total fumonisins (FB 1 + FB 2 + FB 3 ) present in traditional Xhosa maize beer, FB 1 had the highest incidence (with a mean of 76%) in samples containing all three analogues [60]. The study further found the mean total fumonisin levels in the beer samples from the chosen regions of Centane and Bizana in the Eastern Cape Province to be 502 ng/mL and 284 ng/mL, respectively [60].
It is thus useful to apply a comprehensive management approach to reduce mycotoxin levels in crops often used as raw materials in the production of traditional beers, thereby diminishing any potential carryovers into the final beer product [73]. To mitigate challenges around mycotoxins occurrence in African crops, Chibundu [73] suggests applying biocontrol technologies to reduce aflatoxins in maize by planting high-quality seeds, carefully sorting cereal grains, timely harvesting and drying crops, and properly transporting and storing crops. In addition, using sorghum or millet as the main ingredients in the processing of novel beverages instead of using maize, which is highly susceptible to aflatoxin-producing Aspergillus spp., is recommended [73]. Mycotoxin levels in contaminated raw materials can be reduced by processing steps such as sorting, washing, steeping, dehulling, milling, boiling, roasting and fermentation [73].
An emerging and important concern around umqombothi bioprocessing and consumption is the production of toxic biogenic amines from microorganisms used as naturally mixed starter cultures [75,76]. This is because the biogenic amine concentrations are used as an indicator of spoilage in food [75]. When consumed in excessive quantities, biogenic amines can cause adverse health effects [75,76]. For example, many cases of food intoxication are mainly caused by histamine and tyramine [75]. Undesirable effects of histamine may be intensified by other amines such as phenylethylamine, putrescine and cadaverine. When ingested in excessive amounts, histamine is known to cause localised inflammation, rash, diarrhoea, burning and itching, urticaria, vomiting, oedema, palpitations, tingling, nausea and hypotension [76].
Similarly, high levels of tyramine can indirectly cause increased respiration and blood sugar levels, dilation of pupils and swelling of eyes, headache and salivation. Biogenic amines such as agmatine, spermidine, putrescine, spermine and cadaverine can form carcinogenic nitrosamines by reacting with nitrites [76]. In a 2010 study, Magwamba [76] found putrescine to be the most prevalent biogenic amine, and histamine to be the least prevalent in sorghum beer. Furthermore, from the 87 samples analysed for histamine, putrescine, cadaverine and tyramine, 91% contained biogenic amines [76]. A comprehensive analysis of biogenic amines (mg/100 mL) in sorghum beer is shown in Table 5. Similar to findings by Matsheka [75], putrescine was produced in significant amounts (4.04 mg/100 mL) in decarboxylase broth by a Paenibacillus azotofixans bacterial isolate (Table 5) [75].
Bacillus cereus, the only food poisoning pathogen isolated from the beer in the study, produced the highest tyramine (3.45 mg/100 mL) and cadaverine (19.8 mg/100 mL) ( Table 5) [75]. A lack of good hygiene practices during beer brewing is suggested through the detection of putrescine and cadaverine, biogenic amines associated with poor sanitary conditions [76]. It is likely that the present biogenic amines are formed by decarboxylase-positive microorganisms in the beer [76,77]. The used raw materials used for brewing the beer can also bear endogenic biogenic amines [76].
The formation of carcinogenic nitrosamines in umqombothi has been attributed to iron overload, the reaction of biogenic amines with nitrites and fumonisins-producing Fusarium fungi [76,78,79]. N-nitrosamines, which can cause oesophageal cancer or squamous cell carcinoma (SCC) of the oesophagus, have been detected in particular brews of umqombothi [79]. Fusarium moniliforme, a corn saprophyte, is believed to play a role in the production of carcinogenic N-nitrosamines in traditional beer [79]. The annual frequency of SCC rose from the 1930s amongst black South Africans when the staple diet changed from sorghum to maize, with traditional beer being brewed with maize as one of the main ingredients [78,79].
A study in Zimbabwe focused on the consumption of traditional beers closely related to umqombothi showed a correlation between regular consumption and iron overload [13]. A similar study in Limpopo, South Africa, attributed the public health problem of iron deficiency and iron overload to consuming locally produced traditional beers [13]. Iron pots often rust with regular use and consistently release iron oxide residues which are deposited in human tissues as hemosiderin when the beer is consumed [79]. Data from Isaacson [79] show that patients with SCC consume more traditional beer than controls. Importantly, however, a lower incidence is observed in African countries in which the staple food is sorghum [78]. It is also vital to highlight that there are general concerns regarding health challenges and toxic effects related to the consumption of alcohol, especially at high levels. No-for each bacterial strain numbers, two randomly selected strains were tested for the production of a given biogenic amine in decarboxylase broth, and an average was calculated; BGA-biogenic amines; His-histamine; Put-putrescine; Cad-cadaverine; Tyr-tyramine; ND-not detected, NR-not reported. Adapted from Matsheka [75].
Other challenges around the health hazards linked to the production and consumption of traditional beer will continue to persist unless exhaustive scientific investigations are carried out, documented and publicised [1,2,12]. According to Adebo [7], to ensure the safety of fermented foods, less contamination must be ensured in raw materials, whilst ensuring the sterility of processing equipment and all other items during the production of the fermented food. Equally important are hygienic conditions for the handling, packaging and storage of fermented foods in order to mitigate against post-processing contamination, with reported petitions to the government in this regard to provide good hygiene and safe production guidelines to household-level brewers [12,16].
In response, the government has made mention of controlling the production and consumption of home-brewed beer such as umqombothi, especially in rural areas [25,80]. Emphasis is placed on having safe and consistently locally produced beverages which can positively contribute to the economy [16,25]. To achieve both ends, bioprocessing approaches can also assist in ensuring efficient production, consistent composition and safer beer products necessary to stimulate socioeconomic growth, especially in the 21st century [16]. Therefore, the socioeconomic, nutritional, cultural and spiritual significance of umqombothi can only be preserved by closely monitoring process parameters and continually improving production through the application of bioprocessing optimisation approaches [16,72,81,82]. The latter is further discussed in the next section.

Classical Bioprocessing Optimisation Approaches
Brewers and production technicians require optimal bioprocessing interventions to ensure a robust control of process and quality parameters, which are both crucial for beer consumers' acceptance [29]. This demand has necessitated the development of novel optimisation techniques and models [29]. Notably, achieving this has been a challenging task, especially in the bioprocessing of beer (both traditional and western) due to biochemical reactions complexities, time constraints and variable interactions within such processes [29,72].
As a result, the relationship between process input variables and the quality of the product cannot always be clearly discernible [72]. Nevertheless, the efficient application of empiric mathematical and statistical models such as response surface methodology (RSM) yields vital information needed to understand, analyse and predict bioprocess responses necessary to correlate and optimise key input parameters that directly affect the product output [29,81,83]. The prediction response is presented in the form of a second-order polynomial equation, as depicted in Equation (1): where Y is the response variable (optimal production parameter); β 0 is the intercept of the response variable; and β i , β ii , and β ij are coefficients corresponding to the factors x i and x j (i, j = 1, 2, . . . n).
The input variables that affect the response Y are x i and x j . The random error is represented by ε [29,81,83]. In bioprocess optimisation, RSM statistically determines multivariate problems from quantitative data [84]. A three-dimensional graphical view with a fitted mathematical model fully describes the concept of RSM [83]. As such, RSM has been heavily applied in food engineering and biotechnology to screen and optimise process factors [29,81,[83][84][85][86]. In contrast to factorial treatment, RSM-designed experiments provide value predictions of the response variable in relation to the role of independent variables [85].
Although a powerful mathematical tool, RSM is riddled with limitations in determining the linear, interactive and quadratic effects of bioprocess [29,85,86]. In addition, this method increases research labour, time and cost with an increase in the number of experimental runs or input factors [29,[81][82][83][84]. As a result, machine learning methods such as evolutionary algorithms (EA) and artificial neural networks (ANN) have been applied in conjunction with RSM to ascertain biological interactions within these biological processes [29,51,[81][82][83][84][85][86].

Bioprocess Optimisation Approaches Using the Concepts of the 4th Industrial Revolution
Artificial intelligence (AI) generates new industrial paradigms by leveraging "enabling technologies": cloud computing, virtual and augmented reality, advanced embedded systems, bid data, internet of things, and cognitive systems [86]. As a result, AI has become an invaluable resource in law, business and economics, education, science and technology, industry and engineering, social studies and agriculture [86,87]. AI is the use of science, technology and engineering to make machines which can emulate human intelligence such as learning, decision, and problem-solving [86]. AI categories can be divided into expert systems, artificial life, data mining, distributed AI, theory of computation, knowledge representation and systems, genetic algorithms, reasoning, machine learning, constraint satisfaction, natural language understanding, programming, neural networks, belief revision and theorem proving [86].
In bioprocesses involving living cells, active enzymes and metabolites, it is crucial to study, model and optimise the reaction system (i.e., fermentation) to increase the efficiency of the process [88]. Automated online analysis, together with different computer software programs that provide predefined bioprocess optimisation strategies, versatile sample processing, and feed control, is improving the management of complex dynamic biological systems [89]. Other online platforms allow for the ex vivo measurement of extracellular and intracellular enzyme activity, while making the quantitative determination of metabolic flux dynamics possible [89,90]. Furthermore, bioprocess development, especially in biotechnology, has experienced the replacement of empirical strategies by new systematic protocols of experimentation, with better reproductivity and analytical precision accuracy [89].
Qualitative models are being replaced by quantitation, which provides meaningful insights into natural systems [89]. As such, the ambiguity circumscribing molecular systems of the natural work can be hurdled by scientific quantitation tools [89]. The demand for integrating computer science in the field of life sciences has revealed new insights into the interaction of food, microbe and mankind [91,92]. An important new-age tool in this development is ANNs, which are currently the most applied and fastest-growing branch of AI [86]. Classical bioprocess optimisation methods can no longer work in isolation since they ignore the combined interaction between experimental conditions of a process by varying one parameter at a time [88].
Thus, the application of ANNs is increasingly becoming popular due to their powerful data-driven computational prowess, their ability to capture non-linear and complex data and their flexibility in analysing biological interactions in their entirety [88,93]. Reyed [89] described ANNs as "computer-based problem-solving systems of evolutionary computation field based on the principle of evolution theory." This technology as a non-linear multivariate modelling tool is being employed by many researchers in food fermentation, production and bioprocess development to better both the process and the product [87,89,94,95]. The main advantage of ANNs, especially for optimising indigenous food fermentation like that of umqombothi, is its standard framework's ability to use background information to solve problems. In addition, ANNs, in contrast to classical tools such as RSM, possess a generic modulation ability (RSM is useful only for logarithmic approaching variables), while not requiring any adequate practical pre-specification [83,89,96].
The superiority of ANNs overs RSM as a bioprocessing approach in the fourth industrial revolution lie in their inherent abilities: faultless oversimplification of invisible designs, real-time learning, high parallelism, vigorous elucidation, noise and fault tolerance, data classification and pattern recognition, accurate value predictions, good generalisation capabilities, and knowledge competence for treating erroneous and unclear statistics [82,83,89,96]. A major drawback of ANNs is their use of the black box learning technique, which cannot always correlate input variables and the output [93]. In this instance, RSM becomes useful for better interpretation of the interaction between input and response variables [93]. Thus, to elicit an accurate prediction or response, ANNs must be used in combination with RSM [89,93].
The importance of RSM, despite its limitations, must not be underestimated, since it is still one of the most effective methods improving fermentation media, synthetic or otherwise [88][89][90]. With a smaller number of variables, RSM can produce a highly accurate response (or output) in non-linear optimisation [90,91]. In addition, RSM can generate a mathematical model in the form of a 3D plot or a second-order polynomial equation, both useful in industrial applications [88,89,97,98]. As a result, it has become a useful tendency to use a coupled bioprocess optimisation approach involving ANNs and RSM in the design of mathematical models and improvement of food production bioprocesses [81][82][83]. Perhaps in this decade, we will catch a glimpse of the achievement of these tools in accurate bioprocess development, biomathematical modelling, cost reduction and wide application.

Future Directions and Conclusions
The importance and relevance of African traditional foods and beverages have gained interest in the last decade [1,[6][7][8][9]. The health benefits enjoyed by our ancestors in the years gone by are motivating researchers to examine how the same and even better health benefits can be enjoyed today [1,8,20,43,45]. Novel production and bioprocessing methods are being developed to make these foods and their nutrients bioavailable and affordable to produce at a large scale [86][87][88][89]97,98]. Moreover, studies are showing interest in understanding the biological interactions that occur within the entire production and supply chain-from farm to consumer-in order to improve quality, safety and sustainability of the food product [73,99,100]. Metagenomics, metabolomics and nutrigenomics are some exhaustive methods of analysis being used to assess the occurrence, expression and consequences of genes, metabolites and nutrients on a host organism [60][61][62][63][64][65][66][67]101]. At the same time, machine learning and artificial intelligent tools such as fuzzy logic, ANNs, particle swarm optimisation, genetic algorithms (GA) and ant algorithms are being applied to understand biological processes as well as generate optimal substitutes for producers. Researchers are examining the aids of technology to enhance traditional methods of production to modern, cost-effective and efficient processes [1,6,[54][55][56][57][58][59][60][61][62].
The development and further commercial production of South African traditional beer was encouraged by author Dr. Van Der Walt's in 1954 with a study titled "Better Kaffir Beer" [55]. Since then, not much has been achieved with respect to scientific enquiry as an attempt to understand the dynamics involved in the production of such a product [73]. As a result, traditional beer bioprocessing has largely been left unexplored both experimentally and industrially. Fortunately, the introduction of the innovative research tools is enabling research and development in many fields within the biotechnology and food technology spectra, specifically, indigenous fermented foods and beverages [1,7,12,14]. In summary, the possible food and beverage biotechnological advancements are endless, despite the opinions of many critics who believe that potential functional foods, such as umqombothi, should be put to rest [1,7,8,26]. Scientific enquiry in its comprehensiveness can prompt further studies focused on identifying important dynamics involved in food matrices [73]. Furthermore, better understanding of umqombothi and its interaction with man-made processes in a laboratory setting can be translated into industrial success [26,27]. Finally, producers and consumers can and should enjoy the abundance of umqombothi and other indigenous fermented products.
To achieve this, we advocate for necessary steps to ensure safety and the coupling of existing as well as emerging technologies for improved production efficiency, nutritional value and safety of umqombothi. As a result, optimisation approaches such as RSM, ANN and GA, as well as microbial analysis methods such as real-time PCR, metagenomics and 3D cell culturing, are useful technologies for advancing this beer type. For umqombothi, a two-step or three-step bioprocess optimisation approaches involving RSM, ANN and GA in combination with functional metagenomics will yield an easy-to-produce, nutritious, and safe end product.

Conflicts of Interest:
The authors declare no conflict of interest.