Modern Technologies and Their Influence in Fermentation Quality

Since the beginning of enology and fermentation research, wine quality has been parametrized from a chemical and sensory point of view. The main chemical compounds employed nowadays to parameterize the quality of wine or other fermented beverages are acids, polyphenols, volatile particles, and polysaccharide compounds [1]. All these chemical compounds directly influence sensory parameters commonly perceived by consumers such as general acidity, variety character, aroma quality, structure, and overall impression [1].

Before starting to study technologies that enhance alcoholic fermentation quality parameters, there is a need to reduce the incidence of spoilage microorganisms such as Brettanomyces/Dekkera or Zygosaccharomyces rouxii able to produce undesirable molecules such as ethyl phenols or acetic acid [2,3] that mask the influence of positive molecules. Traditionally additives such as SO₂ were used to inhibit these undesirable microorganisms. However, modern legislation started to regulate their use due to allergenic food safety problems [4]. A new technology that reduces the incidence of spoilage microorganisms without generating any health collateral effects for specific consumers, is the use of bio controller technologies [3]. Selected strains of yeast species such as Wickerhamomyces anomalus and Metschnikowia pulcherrima have been proven to be especially efficient against undesirable spoilage microorganisms [3].

Color is the first perception that a wine consumer appreciate in a sensory analysis. This quality parameter depends mainly on the anthocyanin concentration. Modern enology has studied ways to increase the extraction and to increase the stability of these molecules during the winemaking process. Recent technologies such as must replacement and hot pre-fermentative maceration increase the phenolic content and enhance the chromatic characteristics of wine while inactivating polyphenol oxidases enzymes able to degrade colored molecules and promoting condensation between anthocyanins and tannins [5]. Other modern technologies to increase wine color from a microbiological point of view are related to the production of highly stable forms of anthocyanins during alcoholic fermentation. Specific yeasts are able to produce high levels of pyruvic acid that increases the formation of high stable anthocyanins such as vitisin A [1,6] or allow to avoid the malolactic fermentation process [7,8] where color intensity usually gets reduced.

The modern food safety standards demanded by most popular food distributors require wines free of hazards compounds. Additionally, most countries start to stablish legal limits for some hazardous molecules. This fact oblige winemakers to control these undesirable compounds form a winemaking point of view. The main parameters to control are ochratoxin A, biogenic amines [9], ethyl carbamate, sulfur dioxide, allergens, pesticides, genetically modified organisms, physical hazards and phthalates [4].

Modern wine consumers usually prefer wines with moderate ethanol levels. This fact promoted the development of new strategies to reduce the high ethanol levels, especially in warm viticulture areas. One interesting strategy is the use of less efficient yeasts than S. cerevisiae in the conversion of sugar into ethanol. Sequential fermentation inoculations involving Hanseniaspora uvarum show interesting results in ethanol reduction while also increase wine quality parameters such as fruity aroma or color intensity [10]. Additionally, climate change is making it difficult in some countries/regions to control some quality parameters during alcoholic fermentation such as the presence of undesirable microorganisms, excessive sugar, lack of acidity, high pH, imbalanced color, undesirable flavors or food safety problems. Modern wine microbiology management offers interesting alternatives to mitigate these problems [11].

Although traditionally some non-Saccharomyces species have been considered spoilage microorganisms [2]. The use of some specific non-Saccharomyces species allow to control and to improve several wine quality parameters [1,12]. The most popular ones are Torulaspora delbrueckii [13], Lachancea thermotolerans [14,15,16], Metschnikowia pulcherrima [12,17], Schizosaccharomyces pombe [18], Hanseniaspora uvarum [10] and Pichia kluyveri [12]. Some groups are studying the microbiota of vineyards and soils to look for other microorganism different from S. cerevisiae able to enhance quality parameters of alcoholic and malolactic fermentation [19].

Modern biotechnologies based on the use of some conventional and non-conventional yeasts allow to produce wine or beer with functional properties for human health [20]. The last studies show interesting results to improve the content of specific neuroprotectives and neurotrasmitters such as serotonin or melatonin [20].

Most studies involving fermentative industries are focused on alcoholic fermentation. However, during the last decade the knowledge regarding malolactic fermentation has increased due to the industrial difficulties that this process shows in some occasions. The use of lactic bacteria species different from Oenococus oeni and the use of combinations of non-Saccharomyces and lactic bacteria are of current interest [21]. Combinations between Hanseniaspora uvarum, S. cerevisiae and Lactobacilus plantarum show improvements in malolactic fermentation time, wine body and aroma [21].

Other new alcoholic beverages different from wine and beer start to be developed and optimized. One of those modern alternatives to grape wine is cashew apple fermentation. This alcoholic beverage show interesting properties such as low ethanol content and significant amounts of antioxidants such as ascorbic acid or polyphenols. The fermentation process of cashew apple has been optimized using Hanseniospora guillermondii that increases phenyl ethanol and acetate ester [22]. Additionally, the fermentation industry is being optimized in industries different from wine, beer or other alcoholic industries. One interesting example of this is the optimization of itaconic acid production using Aspergillus terrus [23].

Saccharomyces cerevisiae remains the main option to perform alcoholic fermentation due to its high fermentation reliability. Nevertheless, the genome of S. cerevisiae is huge and there is a high variability depending on the selected strain. The use of commercial strains can produce standardized wines without personal differentiations. For that reason, some researchers are developing S. cerevisiae selection processes applied to specific regions and grape varieties to enhance their typicity, a good example is Narince wines [24]. Specific selected autochthonous S. cerevisae strains are able to enhance specific esters and terpenes that increase the sensory quality parameters such as floral and fruity characters. Selections of S. cerevisiae strains from “Vinos de Madrid” viticultural region (D.O.) show a way to preserve regional sensory properties different from those of commercial strains that promote biodiversity while improve the personality of wine in parameters such as fruity or floral characters [25]. Recent studies for Bombino bianc wine show how it is possible to select specific S. cerevisiae strains able to enhance arbutin splitting (β-glucosidase) and with moderate pectolytic activity that improves the quality of wine [26].