African traditional sorghum beers vary slightly in manufacturing processes and product characteristics according to the geographical location of production. Common sorghum-based traditional beers produced in different African countries with variations in alcohol contents are shown in Figure 1. Throughout Africa, sorghum beers with similar or slight variations in process and product characteristics may be known by different names according to the region of production or ethnic origin of the beer. For example, sorghum beer is known as kefir, bantu or utshwala in South Africa (Schwartz, 1956; Novellie, 1968; Novellie and De Schaepdrijver, 1986), pito or burukutu in Ghana, Togo and Nigeria (Ekundayo, 1969; Demuyakor and Ohta, 1991; Sanni, 1993; Sefa-Dedeh et al., 1999), dolo, doro or tchapalo in Burkina Faso, Mali, Senegal and Côte d'Ivoire (Yao et al., 1995; Konlani et al., 1996; Bougouma, 2002), tchoukoutou or chakpalo in Benin, Togo, and northern Nigeria (Hounhouigan, 2003), otika in Nigeria and Ghana (Faparusi et al., 1973; Sefa-Dedeh and Asante, 1988; Chinyere and Onyekwere, 1996), bili-bili, ambga, red kapsiki, or dora-bonga in Chad, Cameroon and Central Africa (Nanadoum, 2001; Nso et al., 2003; Maoura et al., 2005), omalovu, tombo, or epwaka in Namibia, ikigage or awarwa in Rwanda (Lyumugabe et al., 2010), merissa in Sudan (Dirar, 1978), talla in Ethiopia (Steinkraus, 2002; Blandino et al., 2003), mtama in Tanzania (Tisekwa, 1989), munkoyo in Congo and Zambia (Herbert, 2003), doro, chibuku, uthwala or chikokivana in Zimbabwe (Chamunorwa et al., 2002; Togo et al., 2002), busaa in Kenya (Nout, 1980). In Burkina Faso, dolo is produced throughout the country with slight differences in process or product characteristics depending on the producing ethnic groups. Thus, in Burkina Faso, varieties of dolo such as dolo mossi, dagara, lobi, samo, bissa, bobo, turqua are produced by different ethnic groups (Bougouma, 2002; Sawadogo-Lingani, 2010). Similarly, in Ghana, the production of pito which originates from the northern parts of the country is now widely produced throughout the country. There are different variants of pito depending on the method of wort extraction and the fermentation technique practiced by the different ethnic groups in northern Ghana, leading to varieties such as Nandom pito, Kokomba pito and Dagarti pito (Sefa-Dedeh, 1991; Sefa-Dedeh et al., 1999).

Traditional sorghum beers play important socio-cultural and economic roles in Africa. Once prepared in family settings and used in ritual ceremonies in honor of ancestors and spirits to establish communication between the visible and invisible world, traditional sorghum beers have now become a common drink among the general population. Dolo and pito are undoubtedly the most popular ancestral alcoholic drink in West Africa and are widely produced and consumed in both rural and urban communities. In Burkina Faso, about 75% of the sorghum produced is used for the production of dolo which is consumed by nearly 60% of the population (Sawadogo-Lingani et al., 2007). Traditional sorghum beer is almost always used for traditional ceremonies and socio-cultural events such as weddings, baptisms, funerals, enthronements, initiations and festivals (Sanni and Lonner, 1993; Sawadogo-Lingani et al., 2007; Aka et al., 2010; Oyewole and Isah, 2012; Coulibaly et al., 2014).

The production of dolo in Burkina Faso and similar alcoholic beverages in other West African countries is a female dominated activity that generates substantial income and contributes to the socio-economic development of local populations (Kayode et al., 2005; Maoura et al., 2006; Sawadogo-Lingani, 2010; Pale et al., 2011). West African women have a long and well-documented tradition of entrepreneurial skills (Mandel, 2004), particularly in the food processing microenterprises. In Burkina Faso, women who are engaged in the production and sale of dolo, called dolotières, represent about 15% of the women population (Herbert, 2003). These women are often organized into associations or cooperatives and licensed to manufacture dolo and run a cabaret or dolodrome (sale joint for dolo). Depending on production capacity, a single sorghum malt production unit in Ouagadougou, the city of Burkina Faso, or other lager cities such as Tamale in Ghana employs about 4–6 people, including at least two men for the execution of specific tasks, with employees receiving monthly salaries (Sawadogo-Lingani, 2010). In Ouagadougou, it is estimated that 600 dolotières produce 36 million liters of dolo per year, which translates to about 9,000 tons of sorghum malt per year. According to Broutin et al. (2003), the production yield is about 4 liters of dolo per kilogram of sorghum malt in Burkina Faso, 2 liters of tchoukoutou per kilogram of sorghum malt in Benin and 4 liters of chakpalo per kilogram of maize malt in Benin. A survey in 2007, showed that the profits from tchoukoutou production in Benin, range from 2,365 to 17,212 fcfa per month (1 euro = 656 fcfa) depending on beer yield and quantity of raw grains transformed. The income generated from the production and sale of sorghum beers is often used to support household activities or invested in children's education (Kayodé et al., 2007). In Abidjan (Côte d'Ivoire), there are more than a hundred tchapalodrômes (places of production and marketing of tchapalo) (Yao et al., 1995; Enou, 1997; Aka et al., 2008; Fokou et al., 2016). Thus, a real traditional sorghum beer industry has developed in West Africa, providing livelihoods for several families (Kayode et al., 2005; N'Guessan, 2009; Pale et al., 2011). The African Sorghum beer industry brings together different actors in the value chain including cereal farmers producing, transporters, distributors and traders, producers and traders of sorghum malts and traditional beers, and consumers.

Physico-chemical and nutritional characteristics of African traditional beers are sparsely reported in literature. The physico-chemical and nutritional parameters usually reported in literature include pH, alcohol content, dry matter, total sugars, proteins, phenolic compounds and antioxidants (Table 1). Generally, pH varies from 3.2 to 3.6 for dolo and 3.2 to 5.0 for pito. These pH values reported for dolo and pito are similar to the pH of other African traditional beers such as tchapalo from Ivory Coast (pH 3.3-3.6), tchoukoutou from Benin (pH 3.0–3.8), bili-bili from Cameroon and Central Africa Republic (pH 3.5-4.4), red kapsiki from Cameroon (pH 2.4–3.3), ikigage from Rwanda (pH 3.9) and merissa from Sudan (pH 4.0). Alcohol contents also vary from 1.4 to 3.5% (v/v) for dolo and from 1.94 to 4.0% (v/v) for pito whereas dry matter contents range from 3.8 to 8.2% for dolo and from 5 to 7% for pito. It thus appears that African opaque beers are acidic alcoholic beverages, and this high acidity is important for the microbiological safety of these drinks. The pH depends on the method of extraction of sorghum malt wort, particularly, conditions such as duration, temperature during the acidification phase, which is carried out by spontaneous uncontrolled lactic acid fermentation. The dry matter contents of dolo (3.8–8.2%) and pito (5.0–7.0%) are highly variable and lower than that of tchapalo (8.4–8.5%), red kapsiki (7.0–7.5%) and tchoukoutou (15.4–20.2%). Generally, dry matter content of sorghum beers depends on sorghum grain characteristics, malting efficiency and decantation/filtration operation conditions. Traditional sorghum beers contain insoluble substances and yeasts (Rooney and Serna-Saldivar, 1991; Kouame et al., 2015). These insoluble substances are mainly starch fragments and dextrins that have not been degraded during mashing and fermentation (Glennie and Wight, 1986). Similar to dry matter content, the alcohol contents of dolo (1.4–3.5%) and pito (2.0–5.0%) are very variable but remains within the normal range of alcohol contents of other African traditional sorghum beers which generally vary from 2.0 to 5.2% (v/v) as shown in Table 1. The alcohol content of traditional African sorghum beers depends on the duration of the alcoholic fermentation, the concentration of fermentable sugars in the wort and thus on the quality of malt and efficiency of the brewing process. Dolo contains phenolic compounds at higher levels than western beer and white wine (Abdoul-latif et al., 2012). In general, traditional sorghum beers contain starch, sugars, proteins, fats, vitamins and minerals (Chitsika and Mudimbu, 1992). They are rich in calories, B-group vitamins (thiamine, folic acid, riboflavin, nicotinic acid) and essential amino acids such as lysine (Chevassus-Agnes et al., 1979; Lyumugabe et al., 2012). According to Holzapfel (2002), pito contains essential minerals such as zinc (Zn), calcium (Ca), magnesium (Mg) and iron (Fe), which are important micronutrients. Due to its nutritional characteristics, FAO (1995) describes African opaque beer as more of food than a drink. Consumers attribute some therapeutic virtues (laxative, analgesic, anti-malarial, anti-hemorrhoidal, energetic, dietary properties) to their consumption, even though such claims are not scientifically proven (Enou, 1997; Amané et al., 2005; Kayodé et al., 2007; Aka et al., 2010). According to Zaukuu et al. (2016), pito is widely consumed as a ceremonial drink in Ghana for its refreshing taste and nutritional characteristics as it provides consumers with a wide range of important polyphenols, micro- and macronutrients that play important roles in the prevention of diseases related to metabolic imbalances such as gastrointestinal disorders, inflammation, obesity and hypertension. In general, however, detailed information on the nutritional and health benefits of West African traditional sorghum beers are scarce and scanty. For a better valorization of these ethnic drinks, it is necessary to undertake research works to highlight their nutritional values and make these data available and accessible in order to be able to evaluate their real contribution to the nutrient intake and well-being of consumers.

African opaque beers are characterized by the variation in their organoleptic characteristics from one production batch to another (Lyumugabe et al., 2012), due to the artisanal nature of the manufacturing process. As far as organoleptic characteristics are concerned, there is no specific description for dolo and pito. These two drinks, like other African traditional sorghum beers are generally opaque, cloudy, low in alcohol, unfiltered and unstable, and contain insoluble substances and yeasts (Rooney and Serna-Saldivar, 1991; Kouame et al., 2015). African sorghum beers have an acidic or sour taste, which corroborates with their low pH values, have a touch of fruitiness and a characteristic color varying from pale buff to pinkish brown depending on the variety of raw cereal grains used for their production.

The main raw material for the production of African traditional beer is sorghum grains. Common species of sorghum such as Sorghum bicolor, Sorghum vulgare and Sorghum guineese are generally used alone or in combination with other cereal grains such as maize or millet. However, in a few instaces, maize or millet alone is used for the production of African traditional beer (Table 2).

Sorghum grains intended for the production of dolo and other similar African beers must have high starch and amylose contents and a high to medium diastatic power after malting (Dicko et al., 2006; Tchuenbou, 2006). Pigmented sorghum varieties (red or brown) are the most commonly used. White varieties of sorghum are usually not used alone for the production of African beers but often used in combination with red or brown sorghum varieties because consumers prefer colored beers which they also perceive to be healthier (Kayode et al., 2005; Sawadogo-Lingani et al., 2010). In an attempt to select appropriate sorghum varieties for the production of dolo and tchoukoutou in Burkina Faso and Benin, malting properties and brewing characteristics of nineteen varieties of sorghum was assessed (Tchuenbou, 2006). The assessment led to the nineteen varieties belonging to one of three major groups. The first group comprising seven varieties of sorghum (Sotakaman, Zomoaha 2, Natisoya 1, Kioédré, Mewin, Chassisoya, Chabicoman PR) had high diastatic power and high β-amylase activity and were rated excellent for the production of dolo and tchoukoutou. The second group made up of eleven varieties (Agbanni, Natisoya 2, Chabicoman PN, Soniya, Fissouka, Zoueloure, Banninga, Pisnou, Kapelga, Vrac Cotonou, Gnossiconi) with medium amylase activity may also be suitable for sorghum beer, while the last group of one variety (Zomoaha 1) had very low amylase activity and its use as a brewing malt is of little interest among traditional beer brewers (Tchuenbou, 2006). The advantage of all these sorghum varieties is their relatively high availability, presumably due to some favorable agronomic properties and the ability to germinate even after months of storage. In a survey to identify the types and characteristics of sorghum grains preferred for malting and brewing of dolo in Burkina Faso, it was shown that red sorghum is the most preferred grain type because of its consistent ability to sprout well during the malting process (Songre-Ouattara et al., 2016). It is obvious that perception criteria and preferences of the actors (malteuses and brewers) are diverse. It will thus be appropriate to scientifically develop a better systematic and qualitative approach to characterizing sorghum quality attributes for African beer production.

Generally, processors use wort properties such as sweetness as an indicator of the quality of the beer. The sweeter the wort, the better or stronger the beer will become due to available fermentable carbohydrates in the wort.

Different traditional sorghum malting processes in Africa have been reported in literature (Table 2). The main operations that are common to traditional malting of sorghum grains for beer production include steeping of sorghum grains, sprouting and sun drying of sprouted grains. The total duration of the entire traditional malting process varies between 7 and 12 days. Soaking time vary from 5 to 48 h for sorghum malt for dolo production, and from 14 to 48 h for malt for pito production. These steeping times are comparable to those indicated for the malting of sorghum for the production of tchoukoutou (9–24 h), tchapalo (7–12 h), bili-bili (24–72 h), ikigage (24 h) and doro (24 h) (Table 2). Thus, the shortest steeping times are 5–7 h and the longest steeping times are 24–72 h. Soaking of grains during traditional malting process is generally done at room temperature in cans and jars half buried in the ground for better thermal insulation. Steeping brings the moisture content of the grain to levels that are favorable for respiration and metabolic activities and for the mobilization of primary and secondary metabolites, making germination possible. Steeping has an influence on the quality of malt as it contributes to the elimination of flatulence factors (stachyose, raffinose) and the reduction of phytate content through leaching. The quality of sorghum malt (diastatic power, free amino acids and soluble extract) is also positively correlated with the moisture content of the grain at the end of steeping (Dewar et al., 1997). According to the European Brewery Convention (EBC), a well-soaked barley grain should have a final moisture content of about 43–45 and 33–45% for millet and sorghum grains (Aisien and Ghosh, 1978; Malleshi and Desikachar, 1986; Agu and Palmer, 1998; Ogbonna et al., 2004). In addition, water absorption depends on several factors such as the composition of the steeping water, grain variety, grain storage conditions, soaking time and temperature. Soaking conditions for millet and sorghum generally reported in the literature range from 8 to 51 h at temperatures between 25 and 35°C, with most being between 16 and 24 h at a temperature of 30°C. The overall quality of malt increases with the steeping time. The diastatic power of sorghum malt increases with the steeping temperature with an optimum at 30°C while the malt extract and free amino acids are higher with steeping temperature of 25°C (Dewar et al., 1997; Tchuenbou, 2006). Prolonged soaking period can lead to rapid germination, high losses of nutrients (Pathirana et al., 1983; Bhise et al., 1988), or putrefaction of the grains rather than germination (Shambe et al., 1989). For effect of the composition of water, the steeping of the sorghum grain in alkaline water [0.1% of Ca(OH)2, KOH or NaOH] has been shown to significantly enhance the diastatic powre of sorghum malt and β-amylase activity (Okungbowa et al., 2002). Furthermore, aeration of sorghum grains during steeping has a positive impact on malt quality as it leads to an increase in the percentage of sprouted grains, soluble dry matter of the malt, total nitrogen and free amino acids contents (Dewar et al., 1997). Beta et al. (1995) found that malts from sorghum grains soaked in jars with poor aeration had lower diastase, α and β-amylase activity and protein content compared to malts obtained from sorghum grains soaked in an aerated container.

The duration of sprouting varies from 2 to 5 days for sorghum malt used for the production of dolo and from 3 to 5 days for malt used for pito production (Table 2). These durations are comparable to the germination times reported for the malting of sorghum grains for the production of tchapalo (3 days), tchoukoutou (3–4 days), bili-bili (2–4 days) and red kapsiki (2–3 days). Germination of grains in traditional malting takes place at room temperature and away from direct sunlight in cans, baskets, on cemented floors, on tarpaulins or plastic sheets, with watering at variable time intervals to maintain humidity (Fliedel et al., 1996; Bougouma et al., 2008). In air germination, the thickness of the layer can reach 30–50 cm thick. In Burkina Faso, this step may be followed by a maturation phase known as “high germination” where the grains are placed in piles on the floor or in a basket covered with burlap, mats or plastic sheets, with temperatures reaching 60°C at the core of the grain piles (Bougouma et al., 2008). Temperature, germination time and relative air humidity are reported to have significant influence on malt quality. Optimal germination temperatures for sorghum and millet are reported to be between 25 and 30°C. Germination of at 20°C reduces malting losses due to high root growth whereas germination at 30°C causes high losses but increases amylase activity (Agu and Palmer, 1997b). Sorghum malts germinated at 25°C give a better wort quality when compared to sorghum malts germinated at 20°C. Sorghum germination at 30°C for more than 4 days results in a decrease in peptides in the wort (Agu and Palmer, 1999). The α-amylase activity is optimal on the third day of germination and is higher in white sorghum malts than in red sorghum malts, whereas the β-amylase activity is optimal on the third and fourth days of germination (at 30°C) for red and white sorghum respectively (Uvere et al., 2000). The grains are generally germinated at humidities between 85 and 100%. Under uncontrolled moisture conditions such as germination in traditional malting, the grains are reportedly watered at various time intervals i.e., every 8 h (Taylor, 1983), every 6 h (Taylor et al., 1994) or 2–3 times a day based on visual observation of grain dryness (Pelembe et al., 2004).

Germination or sprouting enriches cereal malts with hydrolytic enzymes, sugars, free amino acids, vitamins and improves technological and nutritional quality (Chavan et al., 1981; Malleshi et al., 1989; Taylor and Robbins, 1993; Taylor and Dewar, 1994; Sripriya et al., 1997; Elmaki et al., 1999; Mbofung and Fombang, 2003; Traoré et al., 2004). According to Wang and Fields (1978), germination increases the lysine, tryptophan and methionine contents with an increase in relative nutrient value from - 55.5 to 66.8% (ungerminated kernels) to 78.3–99.5 (sprouted kernels) for maize and sorghum. Demuyakor and Ohta (1992) reported that maltose, glucose and dextrins are the major sugars produced by starch hydrolysis during germination of sorghum varieties in Ghana, while triose, raffinose and xylose appear in small amounts. Traoré et al. (2004) also found significant levels of fructose, glucose and sucrose in sorghum malt from Burkina Faso. On the other hand, germination promotes the release of cyanide due to high concentrations in young shoots and rootlets of germinated sorghum (Panasiuk and Bills, 1984; Aniche, 1990; Ahmed et al., 1996; Uvere et al., 2000; Traoré et al., 2004). However, the removal of rootlets and further processing are reported to reduce the hydrocyanic acid content of malted grains by over 90% (Dada and Dendy, 1988). During traditional sorghum malting, partial polishing of the dried malt by removing part of the roots and stalks is carried out. Similarly, during the brewing of dolo, roots and stalks are also partially removed during the mashing process. According to dolo brewers, this is done to reduce bitterness and astringency in dolo. In Burkina Faso, Traoré et al. (2004) showed that the degermination of sorghum malt promotes a reduction in cyanide content by about 72% and 74% in millet and sorghum malts, respectively, although the process leads to a decrease in amylase and protein contents.

Following sprouting, the germinated grains are sun dried for periods varying from 2 to 4 days for malt intended for the production of traditional African beers (Table 2). However, shorter drying times (6–24 h) are reported for malt intended for the production of tchapalo, bili-bili and red kapsiki. Drying time in traditional malting processes depends on climatic conditions and layer thickness. The green malt is generally spread on the ground, on cemented areas, on mats or plastic sheets, inside concessions, along tared streets, or on the roofs of houses (Bougouma et al., 2008; Aka et al., 2017). Drying times are generally dependent on the intensity of available sunshine and wind speed. During sun-drying, malt is also exposed to bad weather and contaminations from humans, pets, wild birds, city pollution, dust and other impurities carried by the wind.

Drying lowers the water activity of malt thereby favoring the blocking of enzymatic activity, stabilizing and enhacing preservation of the malt (Galzy and Moulin, 1991). The cyanide content of germinated grains decreases during drying (Aniche, 1990; Traoré et al., 2004). The temperature and drying time as well as the relative humidity of the air have an influence on the quality of the malt. Drying temperatures for sorghum and millet malts range from 30 to 65°C with different scales (Aisien, 1982; Lasekan, 1991; Demuyakor and Ohta, 1992). The scale generally chosen is drying at 50°C for 24 h (Beta et al., 1995; Subramanian et al., 1995; Igyor et al., 2001). Amylase activity decreases as the drying temperature increases. Thus, for example, drying sorghum malt at 35, 40, and 45°C reduces its diastatic activity by 7.7, 8.7, and 12.4% respectively (Agu and Palmer, 1996). According to Traoré et al. (2004), sun drying during traditional malting reduces α-amylase activity in millet and sorghum by 16%. Owuama and Ashemo (1994) found low protein and sugar content and thus enzyme inactivation in sorghum malts dried at 65°C compared to those dried at 55°C or at 55°C for 6 h and then 65°C. According to Uvere et al. (2000), drying at 50°C decreases amylase activity and alcohol yield in burukutu. For some authors, the best drying conditions are a temperature of 50 to 55°C, a drying time of 24 h and protection against contamination (Morrall et al., 1986; Owuama and Ashemo, 1994; Uriyo and Eigel, 1999; Uvere et al., 2000; Okungbowa et al., 2002). The evaluation of three stabilization modes (freezing at −18°C, freeze-drying, drying at 45°C) on the amylase activity of sorghum malts showed that all these modes lead to a loss of amylase activity, and drying has a greater negative effect than the other two (Tchuenbou, 2006).

Several studies have shown that optimum malting conditions are different for different millet and sorghum varieties, as varieties react differently to extrinsic factors as temperature and aeration that can influence malting and malt quality (Demuyakor and Ohta, 1992; Subramanian et al., 1995). The rate of water absorption and the saturation water content during steeping depend on the varieties. According to Agu and Palmer (1997a), colored sorghum varieties have a higher α and β- amylase activity than white varieties but gives more losses during malting. Similarly, Eneje et al. (2004) concluded that yellow maize has higher enzyme activity and extract yield than white maize. On the other hand, some studies have reached opposite results, which would reflect the impossibility of absolute grading of kernels with respect to their germination ability according to their color. In addition, high-protein grains yield high-protein malts and extracts (Odibo et al., 2002). Under the same malting conditions, some varieties have their β and α-amylasic activity optimal after 3 and 4 days of germination, while for others these activities continue to increase with germination time (Agu and Palmer, 1997b). There are varieties that produce more α-amylase and/or β-amylases (Dufour et al., 1992; Subramanian et al., 1995) or varieties that are more sensitive to anoxic conditions than others (Beta et al., 1995). Malt quality is defined by its intended use. Thus, for brewing malts, quality is determined by the diastatic power (activity of hydrolysis of starch into fermentable sugars through the activity of α and β-amylase, α-glucosidase and limit dextrinase) and the water-soluble extract. The production of hydrolytic enzymes in malted grains is a complex phenomenon, influenced by extrinsic (environmental and agro-climatic conditions) and intrinsic factors (genetics, grain composition, albumen structure and texture, etc) and malting conditions. The water-soluble malt extract (soluble dry matter) is decisive for having a wort containing fermentable sugars (maltose, glucose) and amino acids needed as a source of carbon and nitrogen for beer yeasts. The conditions of sorghum malting and the factors that can influence the quality of the malt are generally related to an optimum diastatic power, the achievement of a high content of malt extract and free amino acids, and a minimum loss of material during malting. The optimal conditions for the traditional malting of sorghum to obtain a quality malt are soaking to a maximum hydration of 33–36%, germination at 25–30°C for 3–5 days and a drying temperature of the green malt below 65°C (Demuyakor and Ohta, 1992; Agu and Palmer, 1998).

The enzymes generated during malting are essential for brewing operations to obtain a wort rich in soluble matter including fermentable sugars, amino acids and peptides that are also essential for the growth and development of lactic acid bacteria and yeasts. The development of toxinogenic molds and undesirable bacteria in grains during germination can have harmful effects on the quality of malt and finished products, and present health risks for the consumer (Flannigan et al., 1982; Galzy and Moulin, 1991). Malting has a major impact on the composition of sorghum grain, reducing the concentration of anti-nutrients in sprouted grain and improving the bioavailability of certain minerals and overall nutritional quality (Svanberg and Sandberg, 1989; Morero et al., 1991; Mbofung and Fombang, 2003). A reduction in phytates and tannins is generally observed during the malting of sorghum grains and the rate of reduction is a function of soaking and germination times and temperatures (Svanberg and Sandberg, 1989; Mahgoub and Elhag, 1998; Mbofung and Fombang, 2003; Traoré et al., 2004).

The process of brewing traditional African sorghum beer is artisanal in nature and the equipment used are mainly composed of basic materials such as gourds, jars and canaries made of baked clay, cast iron pots, aluminum, iron or plastic recovery barrels, and woven straw baskets. The main source of energy for the brewing of sorghum beer in Africa is firewood with the use of traditional tripod-stone fireplaces, improved fireplaces built in banco and equipped with chimneys (Pale et al., 2010; Sawadogo-Lingani, 2010).

Brewing is the step that produces the fermentable wort for alcoholic fermentation to yield the traditional beer. It is the stage in which starch and proteins are hydrolyzed into fermentable sugars and nitrogen compounds by the enzymes synthesized during malting. Few studies have been carried out on the technological and biochemical aspects related to the traditional brewing of dolo and pito as well as other similar traditional beers. Majority of existing works on African sorghum beers are limited to a description of the traditional processes from various traditional production units as well as the identification of the microorganisms involved in the process (Table 3). Traditional brewing of dolo or pito is a long and complex process lasting for about 48 h (Sawadogo-Lingani et al., 2007; Sawadogo-Lingani, 2010). Figure 2 shows the general flow diagram for the brewing of dolo in Burkina Faso and Dagarti pito in Tamale (Northern Ghana). Red sorghum malt is used exclusively for the brewing of dolo in Burkina Faso by of the Mossi women and other ethnic groups where sorghum malt is generally purchased from malt manufacturing hubs (Malteuses). In South-Western Burkina Faso (Gaoua) and North Ghana (Tamale), dolo or dagarti pito is produced by women of the Dagara and Dagarti ethnic groups from a mixture (50:50) of red and white sorghum malt or with white sorghum malt alone, where the beer brewers produce the sorghum malt by themselves (Sawadogo-Lingani, 2010). The brewing operations for dolo and pito are also similar and generally comprise milling of sorghum malt, mashing, acidification/saccharification, cooking and concentration, cooling, decanting and alcoholic fermentation of the wort by indigenous yeasts (Table 3). Mashing as a sub-operation include diluting the malt flour in water, settling and collecting the supernatant, boiling the pellet, mixing the cooked pellet and the supernatant. The duration of the operations and sub-operations vary among different traditional production units. In the traditional brewing of dolo and pito, the settling time of the aqueous malt flour suspension, which is highly variable (20 min to 12 h), is comparable to the settling times in the brewing processes of Benin's tchoukoutou (1 to 2 h), Côte d'Ivoire's tchapalo (20 to 30 min), Cameroon's bili-bili and red kapsiki (1 to 2 h) and Rwanda's ikigage (3 h) (Table 3).

During the mashing, technological adjuvants are widely used. These adjuvants are extracts of local mucilaginous plants used as flocculating agents to promote settling and clarification of the wort. The plants generally used are yolga (Grewia bicolor Juss), okra [Abelmochus esculentus (L) Moench], baobab leaves (Adansonia digitata), kapok (Bombax costatum), taasalogo (Bridelia micrantha), boundou (Ceratotheca cesamoides) or boulvanka (Chirococus esculentus) (Sefa-Dedeh, 1991; Nanadoum, 2001; Bougouma, 2002; Bougouma et al., 2008; Pale et al., 2010). The aqueous extract of these plants (leaves, bark or fruits) has a sticky appearance and is rich in mucilaginous substances. After settling, the supernatant is decanted into a jar and then the remaining pellet (sediment) is heated to boiling point to gelatinize the residual starch and then mixed with the supernatant. For dolo and pito, the residual starch is heated to a temperature of about 59–68°C. Similar temperatures (65–70°C) have been reported for tchoukoutou, ambga and bili-bili (Lyumugabe et al., 2012; Lango-Yaya et al., 2020). Sorghum starch gelatinization temperatures range between 67 and 81°C (Akingbala et al., 1982). The hydrolytic enzymes in the sorghum malt extract (supernatant) hydrolyze the gelatinized starch and the concentration of fermentable sugars in the must increases. Analogous with modern beer brewing, the principle of mashing is based on infusion and/or decoction to extract fermentable wort by the solubilization of soluble substances in water and the enzymatic hydrolysis of starch and other macromolecules. While barley wort is reported to contain more maltose than glucose (Dufour et al., 1992) sorghum malt worts is reported to contain similar levels of glucose and maltose (Taylor, 1992; Byrne et al., 1993), and the difference has been attributed to the low levels of β-amylase in sorghum malt (Palmer, 1989).

During African sorghum beer brewing, another important process following starch gelatinization and hydrolysis is acidification/saccharification. The mixture of the gelatinized residual startch and the malt wort supernatant is acidified by spontaneous lactic fermentation at ambiet temperature for between 12 and 16 h (Sawadogo-Lingani et al., 2007). This duration is similar to those of the acidification of tchoukoutou wort (13–14 h), tchapalo (9–12 h) and bili-bili (9-18 h), but shorter than the acidification times of chibuku (48 h) and merissa (36 h). This acidification/saccharification is a spontaneous lactic fermentation characterized by a drop in pH and growth of lactic acid bacterial counts reaching 8.8–9.9 log cfu/ml at the end of acidification (Sawadogo-Lingani et al., 2007). The predominance of lactic acid bacteria as the original flora in raw sorghum grains and their proliferation during steeping perhaps give LAB a competitive advantage in the brewing of dolo or pito, leading to their dominance in acidification of sorghum wort (Sawadogo-Lingani et al., 2007, 2010; Sawadogo-Lingani, 2010). The common LAB species involved in the acidification of dolo wort include Limosilactobacillus fermentum (Basonym: Lactobacillus fermentum), Lactobacillus delbrueckii subsp. jakobsenii (Basonym: Lactobacillus delbrueckii subsp. delbrueckii), Pediococcus acidilactici, Lactobacillus lactis and Leuconostoc spp., with a predominance of Limosilactobacillus fermentum (Sawadogo-Lingani et al., 2007; Adimpong et al., 2013; Zheng et al., 2020). Various other species of Lactobacillus, Pediococcus, Lactococcus, Leuconostoc, Enterococcus and Streptococcus genera have also reportedly been associated to the spontaneous fermentation of dolo and pito wort and others similar traditional beers such as Tchoukoutou, Tchapalo, Burkutu, Bili-bili, Chibuku, Otika, Red kapsiki, and Ikigage (Table 3). The spontaneous and uncontrolled lactic acid fermentation found during the steeping of sorghum grains for malting has also been dominated by lactic acid bacteria with Limosilactobacillus fermentum as the dominant species (Sawadogo-Lingani et al., 2010), perhaps giving a competitive advantage to this species during acidification of dolo and pito wort in the brewing phase. Following acidification, the sour supernatant/wort is collected and undergoes boiled for long hours during which water is lost through evaporation and concentrates the wort. In the production of dolo and pito, this boiling can take between 3 and 5 h. This duration of wort boiling is similar to those reported for other African traditional sorghum beers such as tchapalo wort (4–5 h) and chibuku wort (3–5 h), but shorter than the boiling times of the tchoukoutou (6–9 h) and red kapsiki (5–10 h). The boiled concentrated wort is then cooled to room temperature and undergoes alcoholic fermentation.

Alcoholic fermentation of sorghum wort for the production of African traditional beers is generally achieved by the back-slopping technique where part of a previous fermented beer (usually collected from the bottom sediments of previous production) or indigenous dried yeast leaven obtained from previous production is used to inoculate the new batch. The yeast biomass from the previous production is collected, sun-dried and then stored to be used as a local starter culture for subsequent productions. In certain localities, the fresh yeasts are fixed on wooden or fiber supports, or woven belt and these supports are introduced into the canaries containing the wort for fermentation (Sefa-Dedeh, 1991). In most case of African traditional sorghum beers, sorghum wort is inoculated with traditional yeasts and fermentation duration varies between 8 and 24 h at ambient temperature. The duration of fermentation varies from 9 to 14 h for dolo and pito, similar to that of tchapalo (9–12 h) and merissa (8–10 h), but shorter than the fermentation times for tchoukoutou (12–24 h) and bili-bili (12–24 h) while chibuku has the longest fermentation time of about 5–7 days. In Western breweries, the fermentation is ensured by selected yeast strains (S. cerevisae or S. carlsbergensis) and the fermentation time ranges between 8 and 15 days at 10–16°C (Waites et al., 2001). Fermentation is the important step by which yeast converts the sugars of the wort into ethyl alcohol. Interest in the characterization and identification of the yeasts responsible for the alcoholic fermentation of African traditional beers including dolo and pito has been demonstrated in several studies (Table 3). It is found that Saccharomyces cerevisiae is the dominant species responsible for the alcoholic fermentation of dolo and pito as well as other African traditional beers. Other yeast species identified during the fermentation of African sorghum beers include S. pastorianu, S. chavelier, Candida spp., Kloeckera spp., Hansenula spp., Torulaspora spp., Schizosaccharomyces spp., Kluyveromyces spp., Debaryomyces spp., Pichia spp., Dekkera spp., Clavispora spp., Hanseniaspora spp., Rhodotorula spp., Cryptococcus spp. (Table 3). However, most of these yeasts are considered contaminants not taken part in the fermentation; some may even be pathogenic and affect the safety of the traditional sorghum beer.

At the end of alcoholic fermentation, dolo or pito is well frothy and sparkling, and ready for consumption. Traditional sorghum beers such as dolo and pito do not undergo filtration or stabilization and are consumed in the active fermentation state. The dolo or pito is packaged in canaries, jars, plastic buckets or barrels of 20 or 5 L cans for sale to consumers in cabarets or to dolo retailers. At the cabarets, dolo is served and drunk in gourds. African traditional sorghum beers have a poor keeping quality with a shelf-life of about 24–72 h at ambient temperature (Novellie and De Schaepdrijver, 1986; Tisekwa, 1989; Broutin et al., 2003; Maoura and Pourquie, 2009; Lyumugabe et al., 2010; Aka et al., 2017). A few investigations (Osseyi et al., 2011; Dahouenon-Ahoussi et al., 2012; Ayirezang et al., 2016) have been conducted in an attempt to improve the shelf-life of dolo and pito or similar beers. Recent investigations show that the shelf-life of pito can be extended through pasteurization and/or the addition of Moringa oleifera leaf extract for up to 28 days. However, pito samples that contained the moringa extract were less favored by consumers (Ayirezang et al., 2016). According to Dahouenon-Ahoussi et al. (2012), the use of essential oil of Citronella (Cymbopogon citratus) at 1 ml/L was effective in stabilizing African sorghum beer against the spoilage effects of continued fermentation. Rodrigue Christian et al. (2014) also evaluated the influence of Hemizygia bracteosa (Benth) leaf powder on the quality of chakpalo produced in Benin and reported that the use of the powdered leaves during mashing had an effect on the physico-chemical parameters, providing a slightly sweet drink, less acidic, with low alcohol content.