Impact of Spontaneous Fermentation on the Physicochemical and Sensory Qualities of Cacao

Abstract

Fermentation is a fundamental technique that allows us to obtain high-quality cacao beans and derived products. Therefore, it is necessary to apply fermentation correctly to maximize product quality. Fermentation techniques vary by region and include piles, trays, wooden boxes, baskets, and platforms. During these processes, several factors influence the physicochemical and sensory characteristics of cacao beans. The factors that influence these characteristics are the frequency of turning, the genotype of the bean, and the duration of fermentation. This review aims to explore how the fermentation method, turning frequency, bean genotype, and fermentation duration affect the physicochemical and sensory qualities of cacao beans. To this end, an exhaustive search for recent information on the most commonly used fermentation methods in cacao-producing countries over the last 10 years was carried out. The fermentation method in wooden boxes or crates is the most commonly used method worldwide. The most common turning frequency is 24 or 48 h, which is considered the most suitable time for obtaining cacao beans with better sensory attributes, such as floral and fruity aromas, and a lower level of acidity. Finally, a relationship was found between the genotype and the optimal fermentation time of cacao: about 4 days for Criollo cacao, approximately 5 days for Forastero cacao and between 1.5 and 10 days for Trinitario cacao.

1. Introduction

Fermentation is a biological process through which microorganisms degrade organic matter, producing a wide range of compounds with potential health benefits. Historically, fermentation has played a fundamental role in enhancing the microbiological safety and nutritional enrichment of foods and beverages. Globally, food fermentation represents a key biotransformation pathway in which carbohydrates, amino acids, and fats are converted into compounds that enhance flavor and aroma profiles [1], allowing for greater diversification of food products to meet consumer preferences. It also contributes to product preservation, facilitating large-scale storage and distribution without compromising nutritional quality [2,3].

Fermentation is commonly applied to cacao and coffee beans, as well as to cereals such as maize, wheat, and rice. This process can occur through different types of fermentation. Alcoholic fermentation, primarily carried out by yeasts of the Saccharomyces genus, converts sugars from the mucilage into ethanol, which subsequently serves as a substrate for the production of acetic acid by Acetobacter spp. in the presence of oxygen. Acetic acid acts as a precursor in the formation of flavor- and aroma-contributing molecules [4]. Lactic fermentation is driven by bacteria from the Lactobacillus and Streptococcus genera, producing aromatic and antioxidant compounds that enhance the sensory profile of fermented products. Citric fermentation, mediated by fungi such as Candida spp., leads to the production of citric acid, which imparts characteristic fruity notes, as found in citrus fruits. However, not all fermentative processes are desirable; for instance, butyric and propionic fermentation (carried out by Clostridium species) can result in off-flavors and unpleasant odors, which must be avoided in food production [5].

The soybean (Glycine max) is traditionally known as a legume rich in proteins and oils, and is commonly fermented to produce foods such as douchi, sufu, dajiang, tempeh, and natto [6]. This process enhances both the sensory and nutritional properties of the grain [7,8]. The synergistic action of filamentous molds, lactic acid bacteria, and environmental factors (temperature, pH, and oxygen availability) facilitates the breakdown of proteins and carbohydrates [8]. During fermentation, enzymes play a key role in driving important biochemical transformations [6]. Proteases degrade proteins into peptides and amino acids (glutamate and aspartic acid), which are responsible for umami flavor; amylases convert starches into simple sugars that influence the organoleptic profile; and lipases release fatty acids that contribute to aroma compound formation. These reactions promote Maillard and Strecker reactions, which are essential to the sensory (color, aroma, flavor) and bioactive properties of fermented products. Additionally, glucosidases increase the bioavailability of isoflavones by converting them into aglycones, thereby enhancing their antioxidant and anticancer potential [6].

Like the soybean, spontaneous fermentation of maize (Zea mays L.) has been used to improve its nutritional profile. As a result, maize fermentation has been extensively studied and applied in various traditional foods across different world regions [9]. These foods are classified according to the raw material used: dry grain, soaked cobs, corn flour, or crushed maize. Consequently, a wide range of products is obtained, including liquids (ogi and chicha), solids (pozol and kenkey), and dried foods (arraw and wômi) [10]. Similarly, oat fermentation significantly enhances its nutritional profile. This process improves the bioavailability of vitamins, minerals, and bioactive compounds such as antioxidants, while reducing antinutritional factors like phytic acid. Moreover, fermentation contributes to food safety by inhibiting pathogenic microorganisms, improves sensory attributes, and extends shelf life, thereby responding to the growing demand for healthier and more sustainable food products [1].

In contrast to fermentation of soybean, oats, and maize, which primarily enhances nutritional and functional properties, cacao fermentation is mainly aimed at generating key flavor precursors essential for chocolate production [11]. Cacao (Theobroma cacao L.) is the primary raw material for the production of chocolate and other derived products. In the food industry, the quality of cacao beans significantly influences the sensory profile, price, and consumer acceptance of the final product [12,13]. Cacao quality results from the interaction of genetic, environmental, and post-harvest factors. The genotype of the crop and the growing conditions, such as climate and soil, are critical. Pod ripeness at harvest is also important, as sugar content varies with maturity and can influence fermentation. In addition, appropriate post-harvest handling, including fermentation and drying, is essential to enhance the flavor and aroma of cacao and to ensure a high-quality final product [14].

Cacao fermentation is widely recognized as a critical process that generates chocolate flavor precursors and reduces undesirable attributes, largely determining the final physicochemical and sensory characteristics of the cacao [13]. Although interest in fermentation has grown in recent decades, as evidenced by the increase in scientific studies and patents, cacao fermentation has not yet achieved technological maturity. This limitation is due to a combination of economic, infrastructural, and sociocultural factors [15]. Small-scale cacao producers lack access to equipment or training and often rely on traditional, familiar practices that result in heterogeneous fermentation processes [13,16]. However, a thorough understanding of how fermentation influences the physicochemical composition and sensory quality of cacao is essential for improving quality control throughout the chocolate production chain.

Fermentation occurs spontaneously through the activity of naturally present environmental microorganisms, including yeasts, lactic acid bacteria, and acetic acid bacteria [17,18]. These microorganisms metabolize the mucilage surrounding the beans and initiate a series of biochemical transformations within the cotyledons [19]. Yeasts begin the process by converting sugars into ethanol, carbon dioxide, and secondary metabolites that contribute to early flavor development. Subsequently, lactic acid bacteria convert residual sugars and acids into lactic acid, which creates anaerobic conditions that favor the growth of acetic acid bacteria. These bacteria oxidize ethanol into acetic acid. The overall process releases heat, increasing the temperature of the fermenting mass to approximately 45–50 °C. The combination of acid diffusion and thermal increase leads to embryo death and cellular breakdown. This disruption activates enzymatic reactions such as polyphenol polymerization, which reduces astringency and bitterness, and supports the release of flavor precursors through the hydrolysis of proteins and sugars [20,21]. As a result, fermentation plays a central role in the development of aroma compounds in cacao beans [13,22,23]. Flavor is one of the most important attributes of cacao, as it directly affects consumer preference [14].

In practical terms, fermentation is typically carried out in wooden boxes or baskets, depending on regional traditions and resource availability [18,24]. These systems generate different conditions of temperature and aeration, both of which influence microbial dynamics and the performance of the fermentation process [14]. Among these methods, box fermentation is particularly recommended, due to its capacity to regulate environmental variables more precisely. This method allows for better control of temperature and humidity, both of which are essential for the production of desirable flavor and aroma compounds. According to Afoakwa [20], box fermentation ensures more uniform heat distribution and facilitates the removal of excess pulp and juices, thereby minimizing batch variability and promoting a consistent flavor profile in the final product. Additionally, the use of boxes limits exposure to external contaminants and contributes to improved bean quality [25].

Compared to less controlled approaches such as heap fermentation, the box system offers several advantages. According to Kongor et al. [14], it allows for more uniform fermentation through better air circulation and reduces the risk of acid accumulation, which may negatively affect flavor. The ability of the box system to support low-oxygen conditions is particularly beneficial during the early stages of fermentation, which are dominated by yeast activity and ethanol production. These initial events are followed by the activity of lactic acid and acetic acid bacteria. As a result, box fermentation is considered a reliable method for producing more homogeneous and predictable cacao quality.

The objective of this review was to examine how the fermentation method, turning frequency, bean genotype, and fermentation duration affect the physicochemical and sensory qualities of cacao beans. It is important to emphasize that this objective is specifically focused on cacao beans, due to the complexity and uniqueness of their post-harvest processing, which distinguishes them from other types of seeds. Cacao, particularly the Criollo, Forastero, and Trinitario varieties, exhibits a distinctive interaction between genetic characteristics and cultivation conditions, which significantly influences its flavor profile and overall quality. A review by Saltini [25] highlighted the importance of understanding these specific interactions during the fermentation and post-harvest stages, which are essential for transforming cacao seeds into high-quality chocolate.

This focus on cacao is especially relevant given the growing commercial interest in producing fine and premium-quality chocolate in Colombia. The demand for high-quality cacao products that meet gourmet standards has prompted researchers to investigate fermentation practices and their impact on flavor. As noted in the reviews by Campos et al. [26] and Velásquez-Reyes [23], understanding how fermentation methods influence the formation of volatile compounds in cacao is critical to meeting market demands and increasing profitability for producers. This approach is particularly relevant in the case of cacao, as in other agricultural crops quality differences associated with processing are generally less pronounced and less valued by consumers.

This review article addresses the fermentative processes involved in cacao beans, along with their microbiological and biochemical foundations. The role of artisanal and traditional fermentation will be discussed, with reference to other fermented grains such as coffee, soybean, maize, and oats. Furthermore, the influence of fermentation on nutritional value, functionality, and social relevance will be examined, highlighting the opportunities it presents for the cacao industry and reinforcing its importance in promoting sustainable and healthy food systems [27].

2. Materials and Methods

For this review, an exhaustive literature search was carried out of academic databases, such as Scopus, Google Scholar, and Connected papers, using different search strings (search strings (1)–(3)). During the search, keywords such as “cacao genotypes”, “cacao fermentation methods”, “cacao fermentation”, “spontaneous cacao fermentation”, “cacao bean quality”, and “turning time” were used. In addition, Perplexity AI was applied. Articles in English, Portuguese, and Spanish published between 2014 and 2024 were mainly included. Less than 5% of articles were published before 2014. The articles were classified into four categories based on the factors associated with cacao fermentation, which influenced the final quality of the bean (Figure 1). Finally, some conclusions of the search are proposed with reference to coincidences in fermentation times, fermentation phases, and turning of the cacao to oxygenate the mass. This made it possible to confirm the procedure and activities carried out during the post-harvest handling of cacao, especially during the harvesting and fermentation stages. Likewise, within the framework of a controlled process, it will allow the establishment of process control parameters, guarantee decision making based on facts and data, optimize resources, and guarantee products within the specification.

Bibliographic search string 1.

Title-abs-key		Title-abs-key		Title-abs-key		Publication year
Genotypes of cacao		Fermentation of cacao		Fermentation methods		>2014
OR	AND	OR	AND	OR	AND	AND
Cacao genotypes		Cacao fermentation		Fermentation process		<2025

Bibliographic search string 2.

Title-abs-key		Title-abs-key		Publication year
Spontaneous fermentation of cacao		Cacao bean quality		>2014
OR	AND	OR	AND	AND
Natural fermentation of cacao		Quality of cacao beans		<2025

Bibliographic search string 3.

Title-abs-key		Title-abs-key		Publication year
Fermentation methods of cacao		Turning time		>2014
OR	AND	OR	AND	AND
Cacao fermentation techniques		Cacao beans		<2025

Cacao Fermentation Methods Globally

Fermentation techniques vary by region and can range from fermenting cacao beans using the pile method [28,29,30] to trays [31,32], wooden boxes [33,34,35,36], baskets [34,37,38,39], and platforms [38].

Table 1. Fermentation methods used globally.

Region	Country	Genotype	Fermentation Method	References
America	Colombia	CCN-51 Cacao	Wooden boxes	[40]
		CCN-51 Cacao	Wooden boxes	[41]
		CCN-51, LUKE-40, ICS 95	Wooden boxes	[42]
	Venezuela	Criollo cacao	Wooden boxes	[43]
		Forastero cacao	Plastic basket	[44]
	Peru	Cacao beans from the CCN-51 clone	Wooden boxes	[45]
		Criollo cacao and CCN-51 cacao	Wooden boxes, sacks	[46]
		Organic cacao	Wooden boxes	[47]
	Ecuador	National cacao (top)	Wooden boxes	[48]
		CCN51 and National	Rotary fermenter and horizontal wood fermenter	[49]
	Brazil	Fine cacao type Scavina	Wooden boxes	[50]
		Forastero cacao	Wooden boxes	[39]
	Honduras	Carmelo variety cacao (criollo cacao)	Wooden boxes	[51]
	Mexico	CCN51 and National	Rotary fermenter and horizontal boxes
		Cacao clones H12, H13, RIM 44, RIM 88, RIM 105, Carmelo, Criollo INIFAP, and Lagarto	Wooden boxes	[49]
		Criollo and Forastero cacao	Wooden boxes	[23]
Africa	Ghana	Hybrid cacao and the Amazon	Pile	[30]
		Unspecified	Pile	[52]
	Côte d’Ivoire	Mixed varieties	Wooden boxes, pile	[53]
		Unspecified	Wooden boxes	[54]
		Forastero, Trinitario, and Criollo	Pile	[55]
		“Mercedes” (Amelonado × Trinitario	Plastic boxes	[56]
		Unspecified	Wooden and plastic boxes, Pila.	[57]
		Mixed genotypes (Forastero, Trinitario, Criollo)	Pile	[58]
		Hybrid Forastero	Pile, wooden boxes	[59]
	Nigeria	Unspecified	Pile	[60]
Asia	China	Taiwanese cacao	Wooden boxes	[61]
	India	Mixed F1 progeny varieties	Wooden boxes, bamboo basket, pile	[12]
	Indonesia	Unspecified	Wooden boxes	[62]
		Forastero/Trinitario Criollo	Bamboo baskets, wooden boxes	[63]
		Unspecified	Wooden boxes	[64]
	Vietnam	TD3 genotype	Wooden boxes	[65]
		TD3 genotype	Wooden boxes	[66]
		Forastero and Trinitario	Wooden boxes	[67]

summarizes the most commonly used fermentation methods in cacao-producing countries worldwide. Figure 2 shows the different methods used for cocoa fermentation.

Table 1 provides recent information on the most commonly used fermentation methods in cacao-producing countries over the past 10 years. Wooden boxes are the most widely used method globally, regardless of the cacao genotype to be fermented. In Latin America, cacao-producing countries, such as Colombia, Peru, Brazil, Ecuador, and Mexico, mostly use wooden boxes for cacao fermentation. In African countries, wooden crates are also used in countries such as Côte d’Ivoire and Ghana, followed by piles and plastic baskets. Wooden boxes are also predominant in Asian countries such as China, Indonesia, and Vietnam. This pattern suggests that wooden crates are preferred globally because of their effectiveness in controlling temperature and aeration during the fermentation process, which directly affects the quality of the final product. In fact, many of the studies and much of the research use this fermentation technique [68].

The method of fermentation in wooden boxes consists of placing harvested cacao seeds inside a wooden structure with holes and covering them with sacks or banana leaves to maintain humidity and preserve the heat provided by fermentation [49]. In Brazil, the Executive Committee of the Cacao Farming Plan (CEPLAC) advises that fermentation be carried out in wooden boxes that are equipped with removable dividers to facilitate the practice of turning cacao beans. In addition, wooden boxes should have holes 6 to 10 mm in diameter at a distance of approximately 15 cm from each other to drain the liquid formed during fermentation [17].

3. Results and Discussion

3.1. Factors Associated with Cacao Fermentation Influence the Final Bean Quality

Fermentation technique. Cacao fermentation is a microbial process involving biochemical changes that lead to the formation of metabolites of interest within the cacao seeds, serving as precursors of flavor and aroma for the chocolate industry. The process unfolds in three main phases (anaerobic, mixed, and aerobic), in which yeasts, lactic acid bacteria, and acetic acid bacteria play key roles (

Table 2. Role of microorganisms during cacao fermentation.

Microorganism	Action
Yeasts (Saccharomyces cerevisiae, Candida, Kluyveromyces).	Yeasts ferment the sugars present in the cacao mucilage, producing ethanol, which is subsequently utilized by acetic acid bacteria, along with the generation of heat and carbon dioxide (CO2).
Lactic acid bacteria (Lactobacillus, Pediococcus) Maximum exponential growth occurs between 24 and 36 h.	The presence of oxygen promotes an increase in lactic acid bacteria, which convert glucose into lactic acid, mannitol, glycerol, ethanol, and other aromatic compounds within the cacao seed.
Acetic acid bacteria (Acetobacter, Gluconobacter) Maximum exponential growth occurs between 24 and 36 h.	Acetic acid bacteria oxidize ethanol into water and acetic acid. This organic acid penetrates the seed and triggers biochemical transformations of molecules associated with flavor and aroma.

) [69,70].

During the anaerobic phase, which occurs within the first 24 h, yeasts are the predominant microorganisms. Through the glycolytic pathway, also known as the Embden–Meyerhof–Parnas (EMP) pathway, they produce ethanol and other metabolites of interest that promote the growth of lactic acid and acetic acid bacteria [71]. Cacao fermentation is driven by the mucilage surrounding the beans, which contains approximately 80% water, 2% pectin, 15% sugars, and 3% citric acid. This composition acidifies the mucilage to a pH of around 3.5, creating optimal conditions for yeast activation and the metabolism of sugars into ethanol, various intermediate metabolites, and heat. By the end of the first 24 h, the temperature typically rises from 40 °C to 50 °C. Simultaneously, the pH of the cacao mucilage increases from 4.5 to 4.8 [72].

In the mixed anaerobic–aerobic phase, lactic acid bacteria increase exponentially, metabolizing glucose into lactic acid and various other metabolites, all of which are directly involved in the formation of flavor- and aroma-contributing molecules during the fermentation, drying, and roasting of cacao seeds. Certain lactic acid bacteria species can also metabolize fructose into compounds such as citric acid, which enhances the final flavor of the cacao bean [73]. The aerobic phase is initiated by the mechanical turning of the cacao mass (seeds plus mucilage) and by the migration of leachates, which creates interstitial spaces between the seeds, facilitating oxygen penetration. This environment promotes the development of acetic acid bacteria, which utilize the ethanol produced by yeasts and convert it into acetic acid. As this acid migrates into the interior of the cacao bean, it leads to embryo death and initiates the transformation of sugars, polypeptides, and free amino acids into key flavor and aroma compounds [74].

As mentioned above, cacao fermentation can be performed in piles, baskets, wooden boxes, or trays, and each method has its own advantages. The pile fermentation method ensures a uniform process; the method in the box influences pH values, tannins, and sugar content, whereas the tray fermentation method is mainly suitable for short fermentation processes [75]. Guehi et al. [76] determined that fermentation in a plastic box produces cacao of lower quality than fermentation methods carried out in wooden boxes and piles. This could be due to the plastic box material, which could constitute a reducing microbial growth factor. Therefore, the growth of microorganisms was limited and altered. However, biological materials, such as wood and banana leaves, allow for the optimal microbial growth necessary for fermentation. Ale et al. [60] showed that there were no significant differences in the physical characteristics of cacao samples fermented by the pile fermentation method and by the wooden box fermentation technique. The pile method presented better quality in terms of acceptable standards. However, the quality performance of the wooden box was similar to that of the pile fermentation method.

Similar results were obtained by Kononenko et al. [77] and Srikanth et al. [78]. Physicochemical and microbial changes in the cacao beans were evaluated using different fermentation methods (trays, boxes, piles, and baskets). The box method was the best among the methods used for producing high-quality cacao. In [79], the authors evaluated the effect generated by using a wooden rotary and a stainless-steel rotary. The results were compared with those of a traditional wooden box fermenter, where they determined that there were significant differences (p < 0.05) in the average daily temperature between the box fermenter and fermenters with wooden and stainless-steel rotary fermenters. Similarly, the cacao liquor from the box fermenter exhibited more pleasing sensory qualities. In contrast, ref. [80] observed that bacterial and fungal populations were affected by the fermentation method used (boxed, piled, or sacked). Boxed fermentation resulted in a greater diversity of bacterial species, whereas beans processed in the soil had a wider fungal community. Due to the limited microbial diversity present when using other methods, researchers have considered the box fermentation method as a technique that guarantees good fermentation.

Recently, Arulmari and Visvanathan [12] studied the quality of a mixed variety of cacao beans fermented in bamboo baskets, piles, and wooden boxes, with different turning times for a period of 6 days. Several physical and biochemical qualities of dried cacao beans and other parameters, such as pH, temperature, humidity, and microbial population, were evaluated. They concluded that the pile method presented the most desirable quality attributes, including low acidity, which is considered optimal for obtaining high-quality cacao.

Turning frequency. Farmers use different techniques to carry out the fermentation process in an aerobic environment to promote the sensory profile. One of these techniques involves the consecutive turning of cacao beans at different times [81]. Turning consists of mixing the cacao pulp mass to homogenize the temperature and improve the oxygenation of the beans to stimulate the production of acetic acid. An increase in temperature improves fermentation and facilitates enzymatic and nonenzymatic oxidation reactions in beans [82].

The influence of turning during fermentation on the quality of cacao beans was also studied. Some studies have shown that cacao beans that are frequently flipped produce lower acidity [83]. This is because the turning process improves aeration and reduces residual levels of organic products (especially lactate and acetate) in cacao beans [84]. Likewise, aeration prolongs the growth of yeasts, which generates greater consumption of mucilage to convert it into ethanol. In fact, accumulation of ethanol limits the growth of the other groups of lactic acid bacteria. Turning of the cacao beans also causes dissociation of the mucilage and allows the acidic acetic bacteria to oxidize the sugar into ethanol, which volatilizes under aerobic or drying conditions.

The application of turning times during the fermentation of cacao beans has also been studied. Cardona-Velásquez [85] studied the influence of turning at 0 h, 12 h, 24 h, and 36 h on the physical and antioxidant properties of cacao. The 12 h and 24 h turning frequencies generated higher pH and lower acidity levels. Production of the highest concentration of polyphenols was obtained when no turning was performed. Meanwhile, as the turning frequency increased, the polyphenol concentration decreased. In addition, the results indicated that, at a turning frequency of 12 or 24 h, beans with better physical attributes were obtained. However, polyphenol concentrations and antioxidant activity were lower.

Similar results were obtained by [86], who avoided turning during the fermentation of cacao in piles and in a box. During this process, high levels of acidity and polyphenols are generated in the beans. On the other hand, when the cacao was turned, astringency, bitterness, and acidity were lower compared to the treatment without turning, which improved the aroma of the cacao and decreased the growth of molds and the formation of ochratoxin A. In [36], the authors also reported that turning cacao during box fermentation improves the volatile compound profile. Turning cacao increases the production of chemicals, such as benzaldehyde, 2- and 3-methylbutanal, and esters, such as ethyl acetate, produced through increased stimulation of lactic acid bacteria. In addition, acetoin and acetic acid were favored by greater stimulation with acetic acid bacteria.

Velázquez-Reyes et al. [23], studied two artisanal fermentation processes of Criollo cacao beans with two times of cacao turning times (24 and 48 h). The aromatic profile of cacao with a turning time of 24 h showed volatile compounds associated with aromas such as bread and fruits. When the turning time was 48 h, volatile compounds associated with floral, woody, sweet, fruity, and chocolate aromas were identified. Arulmari and Visvanathan [12] also studied the effect of two cacao turning intervals (12 and 24 h) and used different fermentation techniques (wooden boxes, baskets, and piles). The cacao turning intervals at 12 and 24 h were comparable in the boxed and basket fermentation methods. The pile fermentation method with a cacao turning interval of every 12 h resulted in a lower acidity level compared to the other techniques. In addition, during the pile fermentation method with 12 and 24 h turning intervals, the percentage of brown beans was higher, suggesting that regular turning during fermentation improves bean quality.

Genotype and fermentation time. Theobroma cacao L. encompasses numerous varieties with high genetic diversity. Most commercial cacao comes from three main genetic groups: Criollo, Forastero/Amazonian, and Trinitario [87]. Several studies have shown that the type and amount of precursors, together with the enzymatic activity that contributes to the formation of chocolate flavor and aroma, are closely linked to the cacao genotype [14,87,88]. Aroma and flavor are the most influential factors affecting the quality and commercial value of cacao. However, post-harvest stages, such as fermentation, drying, and roasting, are essential for obtaining quality cacao, and these can enhance the quality of each genotype [88,89,90].

The biochemical compositions of the different cacao genotypes varied. When genotypes are subjected to processes such as fermentation, various flavor precursors are generated, including free amino acids, peptides, reducing sugars, and organic acids, which are responsible for the characteristic acidic notes of cacao. These compounds interact during the drying and roasting processes, resulting in the formation of products with distinct sensory profiles. These sensory variations may be related to interactions between genetic and biochemical factors [14,87,91].

Afoakwa et al. [20] analyzed the role of both volatile and non-volatile chemical compounds in defining the sensory attributes of cacao. Notable among these are polyphenols, methylxanthines, and organic acids, which contribute to specific flavor and aroma characteristics. Their interaction with post-harvest processes, particularly fermentation, drying, and roasting, adds further complexity to the resulting sensory characteristics. Maillard reaction products generated during roasting are particularly important, as they are essential for the development of distinctive aromatic notes. This underscores the fundamental role of chemical transformations in the production of high-quality chocolate [23,25].

Putri et al. [92] emphasized the wide diversity of chemical compounds involved in shaping the sensory characteristics of fine-flavor cacao. Their research demonstrated that molecules such as nitrogen-containing heterocycles, aldehydes, ketones, and esters play a critical role in flavor and aroma development. Each group contributes distinct sensory notes, including fruity and floral tones derived from esters and earthy nuances associated with pyrazines. This body of evidence reinforces the idea that the complex chemical matrix of cacao, shaped by genotype and fermentation conditions, is fundamental to the production of chocolates with unique and appreciated sensory qualities [20,25,93].

Likewise, several studies have reported the influence of volatile acids and phenolic compounds on the sensory profile of cacao [94]. Compounds such as lactic acid and acetic acid modulate cacao acidity and can impact the overall flavor perception of chocolate. Additionally, compounds like proanthocyanidins contribute to bitterness and astringency, sensory attributes that are particularly pronounced in specific cacao varieties. This perspective highlights how individual components interact to shape the sensory complexity of chocolate [14,94].

Table 3. General characteristics, aromatic profile, flavor, and type of use in chocolate of the three main cacao varieties.

Characteristics	Criollo	Trinitario	Forastero
General	Mainly grown in Latin America and is valued for its high quality.	Mainly grown in Latin America and tropical regions. It is a hybrid that combines the quality of the Criollo variety with the robustness of the Forastero.	Mainly grown in West Africa and South America. Of lower quality compared to Criollo and Trinitario.
Aromatic profile	Fine and delicate aroma (it includes compounds such as 2-methylpropanal, phenylacetaldehyde, 2,3,5-trimethylpyrazine, and others that contribute to its distinctive aroma).	Balanced and varied aroma. (It combines floral, fruity and nutty notes. Pyrazines and aldehydes contribute to its aroma.)	Less complex aromatic profile, aroma with strong and bitter notes.
Taste	Soft, sweet taste, with less bitterness, accompanied by fruity, vinous and citrus notes, with a slightly bitter touch.	Balanced flavor, combining the softness of the Criollo with the intensity of the Forastero. It is fruity, with notes of nuttiness, vinous and aromatic, and presents a balance between bitterness and sweetness.	Strong flavor, highly astringent and bitter, with less sweetness, with fruity and earthy notes.
Use in chocolate	Preferred for fine chocolates.	Medium- to high-quality chocolate, it is widely used in the industry for its versatility.	Used in commercial and lower quality chocolates. Due to its intensity, it is useful for mixing.
Production	Lower production due to susceptibility to disease and lower yield, more expensive.	Intermediate production. It is less susceptible to diseases compared to Criollo, but more delicate than Forastero.	Higher production, more accessible globally. It is known for its high performance and resistance to diseases.

Adapted from Farghal et al. [95] and Kongor et al. [14].

compares the general characteristics, aromatic profile, flavor, and type of chocolate used in the three main varieties of cacao: Criollo, Trinitario, and Forastero. Likewise, differences that allow the selection of a genotype according to the characteristics expected in the final product can be observed.

Fermentation time is a critical variable in cacao processing and can determine the type and quality of cacao [89]. Fermentation time has a direct impact on the concentrations of phenolic compounds, lipids, and proteins, which are essential for the development of volatile compounds, acids, and other components responsible for the intensity of the characteristic flavor and aroma of cacao [17,88]. It has been observed that an adequate fermentation time is crucial to maintain an optimal balance between acidity and volatile compounds, which are determinants in the sensory profile of cacao [17]. Some studies suggest that 6 days of fermentation is sufficient to produce volatile compounds, such as esters and other aromatic compounds, which lend desirable flavor notes to Forastero cacao beans. Likewise, a balance of acids is achieved at acceptable levels, which improves the quality of cacao. On the other hand, prolonged fermentation for more than 6 days can lead to the production of undesirable compounds due to overfermentation, which induces a decrease in the quality of cacao [17]. According to Anita [91], in genotypes such as DR 2 (Trinitario), controlled fermentation for 4 days produced aromatic profiles with floral and fresh fruit notes. However, longer fermentation of the other genotypes resulted in more intense aromas of dried fruits and nuts.

In a study conducted in the Amazon region of Brazil, researchers fermented a variety of Forastero cacao for 7 days. In the microbiological analysis of cacao, they identified several species of yeasts, such as Saccharomyces cerevisiae, Pichia kudriavzevii, and Torulaspora delbrueckiiel, which are ideal microorganisms in the fermentation process. These yeast species convert the sugars present in the cacao pulp into ethanol, which induces several biochemical reactions, including degradation of pectins and modification of the acidity profile of the bean. In addition, the study highlights that the fermentation temperature increases significantly during the first 48 h, which is essential for elimination of the embryo and modification of the bead structure, directly affecting the quality of the final product [17].

Although fermentation time is a determining factor for cacao quality, it is not possible to establish a fermentation time for all types of cacaos. It has been shown that each genotype requires different fermentation times to generate a quality flavor and aroma [88]. Similarly, environmental conditions during the fermentation and drying processes influence the characteristics of the final product [17,89]. In the first context, Afoakwa et al. [20] emphasized that the duration of fermentation varies according to the genotype of the cacao beans. In particular, Criollo cacao requires between 2 and 6 days of fermentation, Forastero cacao generally needs 5 days, and Trinitario cacao shows greater variability, with times ranging from 1.5 to 10 days. In [88], the authors obtained similar results when evaluating the fermentation time for each of the cacao varieties (Trinitario, Forastero, and Criollo) grown in Soconusco, Chiapas, Mexico. The researchers correlated the fermentation time with physicochemical variables and the presence of aromas in cacao samples. Likewise, in their study, they determined that Criollo cacao reached its optimal fermentation in 3 days and had a pH of 3.7 in the pulp, a titratable acidity of 0.226%, reducing sugars of 2.3 mM, and 5.4 °Brix. In contrast, Forastero cacao required 5 days of fermentation, presenting a pH of 3, titratable acidity of 0.508%, reducing sugars of 8.02 mM, and 6 °Brix. Similarly, Trinitario cacao consolidated its fermentation time in 5 days with a pH of 3, titratable acidity of 0.789%, reducing sugars of 8.86 mM, and 6.4 °Brix. These times were validated by the presence of pleasant aromas and flavors in the samples and no signs of over-fermentation. According to these results, the fermentation times for each type of cacao were within the range established by Afoakwa et al. [20].

As shown in Figure 3, each cacao variety (Criollo, Forastero, and Trinitario) exhibits a distinct progression of aromas and flavor notes throughout the fermentation period. This reinforces the notion that the sensory profile of each genotype evolves according to the duration of fermentation. It also indicates that each cacao type reaches an optimal fermentation time at which sensory attributes are maximized, prior to the emergence of undesirable characteristics associated with over-fermentation. These findings are consistent with the research conducted by De Vuyst and Weckx [18], who highlighted that microbial activity and metabolite production during fermentation are strongly influenced by the cacao genotype and the dynamics of the process. Similarly, Calvo et al. [74] emphasize that inadequate fermentation management can impair flavor development and lead to a significant decline in overall cacao quality, underscoring the importance of monitoring sensory transitions throughout the fermentation process.

Chagas Junior [17] studied the physicochemical behavior of cacao beans during a fermentation time of 7 days. During the study, the researchers found that there were no significant variations in moisture, ash, lipid, or protein content throughout the process. However, they observed an increase in total titratable acidity after the first 48 h, from 11.54 ± 1.76 meq. NaOH 0.1 N/100 g up to 52.3 ± 2.35 meq. NaOH 0.1 N/100 g NaOH, indicating an increase in microbial activity. This acidity influences protease activity, which in turn affects the development of chocolate flavor.

As mentioned above, the final quality of cacao bean is influenced by both the fermentation time and the drying time, which in turn can be affected by the environmental conditions in which they develop. In [89], the authors used Hybrid C 70 clonal cacao as study material and combined four fermentation times (5, 6, 7, and 8 days) with three drying periods (4, 5, and 6 days). The process was carried out under climatic conditions characterized by high relative humidity between 70% and 90% RH and temperatures of approximately 30 °C. The most important findings allowed us to conclude that, under the climatic conditions studied, a fermentation period of 8 days combined with a drying period of 6 days resulted in cacao beans with a moisture content below the standard (7.5%). These parameters minimize the incidence of fungus in the beans, a low content of purple and slate beans, and an overall purity of 98%, indicating the superior quality of the cacao beans. The number of beans per 100 g increased with fermentation and drying time. The authors concluded that a long fermentation time coupled with longer drying periods induced nutrient loss, resulting in lighter beans.

In line with these findings, other studies have reported significant physicochemical and biochemical changes in cacao beans as a result of fermentation. Peláez et al. [96] documented notable differences between fresh and fermented beans, particularly in pH, total acidity, and moisture content. Fresh beans exhibited a pH close to neutral (6.99 ± 0.20 in the cotyledons), whereas fermented beans presented lower pH values due to acid production, reaching 4.76 ± 0.03 and 4.79 ± 0.01 in beans fermented manually and semi-mechanically, respectively. Total acidity increased accordingly, with values of 2.88 ± 0.18 g of acetic acid per 100 g in manually fermented beans and 2.34 ± 0.18 g per 100 g with semi-mechanized fermentation. Moisture content also declined, from 51.89% in fresh beans to 46.33% and 42.77% with manual and semi-mechanized methods, respectively.

Fermentation also induces marked changes in the chemical composition of cacao. Polyphenols and anthocyanins—responsible for antioxidant capacity and pigmentation—decline as fermentation progresses. In fresh beans, the polyphenol content is approximately 7.0 g GAE per 100 g, decreasing to 5.88 ± 0.56 g GAE per 100 g after semi-mechanized fermentation. A similar trend is seen in reducing sugars, which fall from 3.83% in fresh beans to 2.61% in fermented ones. These compositional changes are indicative of the complex biochemical reactions occurring during microbial activity, with direct implications for the organoleptic, nutritional, and functional properties of cacao.

Lares-Amaiz et al. [97] reported similar trends in cacao beans from Chuao. Bean weight declined from an average of 2.14 g to 1.87 g post-fermentation, primarily due to mucilage degradation. The fermentation process also increased moisture content from 32.50% to 46.32%, lowered pH from 6.48 to 5.30, and raised total acidity from 1.72 to 1.83 meq. NaOH/g of sample. Fat content increased from 45.45% to 50.56%, while the fatty acid profile remained largely unchanged. Protein content decreased from 14.42% to 13.03%, and ash content from 4.30% to 3.46%. These fluctuations are closely associated with the metabolic activity of fermentative microorganisms and the subsequent drying process, both of which shape the quality and processability of the beans.

Husna et al. [98] further emphasized the sensory implications of fermentation. Their study showed that fresh beans, while rich in antioxidant polyphenols, present strong bitterness and astringency due to elevated levels of phenolic compounds and citric acid. Through fermentation, particularly over 3 to 5 days in 20 and 40 kg fermentation boxes, a 20–30% reduction in bitterness and astringency was achieved. Notably, the highest flavor intensity was observed after 5 days of fermentation in a 20 kg box, accompanied by enhanced total acidity and a significantly lower proportion of slaty beans. These improvements not only contribute to a more refined sensory profile but also help meet the quality requirements of premium chocolate markets.

The results from Peláez et al. [96], Lares-Amaiz et al. [97], and Husna et al. [98] underscore the pivotal role of fermentation in transforming fresh cacao into a product with optimized chemical and sensory characteristics. They also reinforce the importance of defining optimal fermentation and drying parameters that maximize quality while minimizing undesirable outcomes, such as nutrient loss or excessive degradation.

3.2. Perspectives

Cacao fermentation constitutes a critical process in determining the final quality of chocolate. From a scientific standpoint, it is essential to undertake a comparative assessment of spontaneous fermentation methods and controlled fermentations that employ defined starter cultures tailored to specific cacao genotypes. Spontaneous fermentation fosters broader microbial diversity, which contributes to the development of complex and distinctive sensory profiles. In contrast, the use of starter cultures enables process optimization and standardization, although it may reduce microbial diversity and, consequently, limit certain unique sensory characteristics. Future research should aim to identify integrative strategies that combine the benefits of both approaches, preserving microbial and sensory richness while ensuring consistent and reproducible quality standards. These efforts are particularly relevant in response to the growing demand for premium and differentiated chocolate products in the global market.

Another key perspective for the advancement of cacao fermentation lies in the implementation of real-time monitoring systems based on advanced technologies, including artificial intelligence (AI), sensors, and Internet of Things (IoT) platforms. The adoption of such tools would allow for automated and precise control of critical variables throughout the fermentation process, including temperature, humidity, oxygen availability, and the concentration of key metabolites. Continuous access to real-time data would support informed decision-making by producers, facilitating accurate determination of the optimal fermentation duration, the ideal turning frequency, and the precise endpoint of the process. Collectively, these technologies have the potential to enhance the quality and consistency of fermented cacao.

Finally, future studies should place greater emphasis on exploring the interaction between specific cacao genotypes and fermentation methods, with particular attention paid to the combined effects of these factors on the chemical composition and final sensory profile of the fermented beans. A comprehensive understanding of these relationships could contribute significantly to the development of customized fermentation protocols for particular varieties, supporting the production of cacao products that align with the specialized demands of high-value markets.

4. Conclusions

The optimal fermentation of cacao requires precise control of methods, duration, and turning intervals. Wooden box fermentation, with its ability to provide better uniformity and control, is globally preferred despite its higher cost and maintenance needs. Implementing real-time monitoring systems enables producers to enhance process efficiency and optimize the organoleptic qualities of cacao, adapting to the specific requirements of different genotypes.

The use of box fermentation systems in cacao processing enables more precise environmental control, optimizing key factors such as temperature and humidity to support the formation of desirable flavor and aroma compounds. This method also promotes uniform heat distribution, facilitates the efficient removal of pulp and juices, and reduces variability in product quality, contributing to a more consistent sensory profile in the final chocolate. In addition, by limiting exposure to external contaminants, box systems help preserve the quality of fermented cacao, ensuring a product with higher commercial value.

Compared to other methods, box fermentation offers significant advantages by allowing for more accurate control of critical environmental variables, particularly during the initial stages of the process. This effective management promotes optimal microbial activity, resulting in more homogeneous and predictable outcomes in final bean quality. These benefits are especially relevant in the context of increasing demand for high-quality products in international markets.

Although the process of spontaneous fermentation of cacao is relatively simple, it requires precise control of parameters such as the fermentation method, duration of fermentation, and turning intervals that enhance the quality of the cacao beans according to the genotype treated or its mixtures.