What is Fermentation?
Fermentation is a metabolic process that induces chemical changes in organic substrates by the activity of enzymes. This includes the separation of energy from carbohydrates in the absence of oxygen. It can be more generally referred to as any mechanism in which the action of microorganisms results in a beneficial improvement in food or beverage. Animal or plant tissues are exposed to the activity of microorganisms and/or enzymes to create beneficial biochemical modifications and major changes in food content are referred to as fermented foods.
Importance and Benefits of Fermented Cereals
Fermented foods make up approximately one-third of the world’s diet. Cereals are especially valuable substrates for fermented food in all parts of the world and are staples in the Indian subcontinent, Asia and Africa. Fermentation induces improvements in food quality indexes, including texture, taste, appearance, nutrition and protection. The advantages of fermentation can include increase in palatability and acceptability by cultivating enhanced tastes and textures; protection by the formation of acidulants, alcohol and antibacterial compounds; enrichment of nutritional content by microbial synthesis of essential nutrients and by improving the digestibility of proteins and carbohydrates; elimination of anti-nutrients, natural toxicants, and reduction in cooking times.
The content and quality of cereal proteins may be improved by fermentation. Natural fermentation of cereals increases their relative nutritive value and available lysine. Bacterial fermentation involving proteolytic activity is expected to increase the biological supply of essential amino acids rather than yeast fermentation, which primarily degrades carbohydrates. Starch and fiber begin to decline during cereal fermentation. While fermentation will not be required to change the mineral content of the substance, hydrolysis of chelating agents such as phytic acid during fermentation increases the bioavailability of minerals. Changes in the vitamin content of fermented cereals differ based on the fermentation process and the raw material used for fermentation.
Classification of Fermented Cereals
Fermented cereal-based food products produced in African countries can be categorized on the basis of either the raw cereal ingredients used in their processing or the texture of the fermented product.
Classification on the basis of raw cereal ingredients:
- a) wheat-based foods e.g. bouza, kishk
b) rice-based foods e.g. busa
c) maize-based foods e.g. ogi, bread, kenkey
d) millet based foods e.g. kunuzaki
e) sorghum based foods e.g. pito, ogi, bogobe, kisra, burukutu, kisra, injera
f) barley based foods e.g. beer
Classification on the basis of texture:
- a) liquid (gruel) e.g. ogi, mahewu, burukutu, pito, uji
b) solid (dough) and dumplings e.g. kenkey, agidi
c) dry (bread) e.g. kisra, injera
Fermented Gruels and Non-Alcoholic Beverages
Ogi
Ogi is a porridge made from fermented maize, sorghum or millet in West Africa. It is the mainstay of the area and acts as a weaning meal for children. Traditional ogi preparation requires the soaking of corn kernels in water for 1 to 3 days, accompanied by wet milling and sifting to extract bran, hulls and germs. The pomace is processed in the sieve and later discarded as animal feed while the filtrate is fermented (for 2-3 days) to produce ogi, which is a sour, white starchy sediment. Ogi is also sold as a wet cake covered in leaves or translucent polythene containers. It is diluted to a solid content of 8 to 10% and boiled in a pulp or cooked to form a rigid gel called “agidi” of “eko” before ingestion.
Banku
Banku is a common staple food in Ghana. It is prepared from maize and/or a combination of maize and cassava. The preparation of banku includes steeping the raw material (maize or combination of maize and cassava) in water for 24 hours, followed by wet milling and fermentation for 3 days. The dough is then combined with water at a ratio of 4 parts of the dough to 2 parts of the water; or 4 parts of the dough to 1 part of the cassava and 2 parts of the water. Continuous stirring and kneading of the fermented dough is important to ensure proper consistency during subsequent cooking.
Kenkey
This is a fermented maize dough that is popularly eaten in Ghana. During the manufacturing process, the dough is split into two parts: one part, the ‘aflata’ is cooked into a thick porridge, while the other part, uncooked, is later mixed with the ‘aflata.’ The resulting mixture is shaped into balls and covered in a dried corn husk or plantain leaves, after which it is steamed. It is important to note that kenkey varieties differ widely across Ghana. In northern Ghana, sorghum is often used as a preparation for the dough instead of maize.
Mahewu
This is a fermented maize meal widely used as a staple by black South Africans. Traditionally, it is prepared by adding one part of the maize meal to 9 parts of the boiling water. The suspension is cooked for 10 minutes, cooled and then moved to the fermentation container. At this point, wheat flour (about 5% of the maize meal used) is added to act as a source of inoculum. Fermentation takes place in a humid, sunny environment within 24 hours. Streptococcus lactis is the primary fermenting organism in typical mahewu.
Mahewu is known to offer some advantages over ogi in that the initial fermentation by fungi, etc. is eliminated by boiling both the maize meal and the steeping water. In addition, it is pre-cooked and requires mixing prior to consumption only. Mahewu consists of coarse corn particles, while ogi contains very fine pasty corn particles.
Mawe
Mawe is a sour dough made from partially dehulled maize meal that has undergone natural fermentation for a period of one to three days. Quantitatively mawe is less important than ogi, but is suitable as a basis for the preparation of many dishes, including those made from ogi. Traditional mawe production involves cleaning maize by winding, washing in water and crushing in a disk plating mill. The crushed maize is screened by sifting, whereby the grits and hulls are separated by gravity and the fine endosperm fraction collected in the bowl.
Injera
Injera is one of the most popular baked products in Ethiopia. It is a fermented sorghum bread with a very sour flavor, and it is the undisputed national bread of Ethiopia. The baked food is referred to by various names based on the place of production in Ethiopia. It is referred to as ‘bidena’ in Oromigua, ‘taeta’ in Giragigua, and ‘solo’ in Walaytigna. Sorghum grains are decoupled manually or mechanically and milled into flour which is then used in the preparation of injera.
Three categories of injera can be differentiated on the basis of processing procedures.:
- thin injera resulting from the mixture of a portion of fermented sorghum paste with three parts of water and boiling to yield a substance known as ‘absit’ which, in turn, is combined with a portion of the original fermented flour.
- The thick injera, which is reddish in color with a sweet flavor, is a ‘tef’ paste which has undergone only partial fermentation for 12-24 hours;
- komtata-type injera, which is produced from over-fermented paste, and has a sour taste. The paste is baked or grilled to make a bread-like product. Yeasts are the primary microorganisms active in the fermentation of the sweet form of injera.
Kisra
This is a thin pancake-like leavened bread made from whole flour of sorghum. It’s a food staple in Sudan. This fermented sorghum bread has a very sour taste. It is prepared by mixing sorghum flour with water to give a thick paste which is allowed to ferment for 12-24 hours, after which the paste is diluted to a desirable consistency with water just before baking.
Kishk
Kishk is a fermented food made from parboiled wheat and milk. It is eaten in Egypt and in most Arab countries. During the preparation of the kishk, the wheat grains are boiled until they are smooth, dried, milled and sieved to extract the bran. Milk is separately soured in earthenware pots, condensed and mixed with moistened wheat flour, resulting in the preparation of a paste called hamma. The hamma is allowed to ferment for around 24 hours, after which it is kneaded and two volumes of soured salted milk are added before dilution with water. Alternatively, milk is added to the hamma and fermentation is allowed for a further 24 hours. The mass is fully combined, shaped into balls and dried. Kishk is a highly nutritious food with a protein content of about 23.5 per cent. It has a high digestibility and a high biological benefit.
Bogobe
Bogobe is a sorghum porridge produced in Botswana from fermented and non-fermented sorghum. Fermented bogobe is a soft porridge, known as ting, while unfermented bogobe is a thick porridge called monokwane.
Kunu-Zaki
It is a millet-based non-alcoholic fermented liquor commonly consumed in northern Nigeria. However, because of its soothing qualities, this beverage is being more widely consumed in southern Nigeria. This is obtained by the steeping of millet grains, the wet milling of spices (ginger, cloves, pepper), the wet sieving and the partial gelatinization of the slurry, accompanied by the addition of sugar and bottling. Fermentation, which happens temporarily during steeping of grains in water over a span of 8-48 hours, is considered to include primarily lactic acid bacteria and yeasts.
Burukutu
It is a popular, vinegar-like alcoholic beverage consumed in the Savannah region of Northern Guinea, Nigeria, the Republic of Benin and Ghana. Burukutu preparation requires steeping sorghum grains in water overnight, after which excess water is drained. The grains are then scattered over a mat or tray, covered with banana leaves and allowed to germinate. During the germination process, the grains are rinsed on alternating days and turned over at intervals. Germination lasts for 4-5 days before the plume exceeds a certain period of time. The malted grains are laid out to dry in the sun for 1-2 days, after which the dried malt is ground into a powder. Gari (a fermented cassava product) is added to the mixture of ground malt and water in a ratio of one part gari to two parts malt and six parts water. The resulting mixture is allowed to ferment for 2 days, after which it is boiled for about 4 hours and allowed to mature for another 2 days. The resultant product is a cloudy alcoholic beverage.
Pito
Pito is the popular beverage of Binis in the mid-western region of Nigeria. It is now commonly consumed in Nigeria due to its refreshing quality and low price. Pito is also commonly used in Ghana. Pito preparation involves soaking cereal grains (maize, sorghum or a combination of both) in water for 2 days, followed by malting, and allowing them to sit in baskets lined with moistened banana leaves for 5 days. The malted grain is roasted, combined with water and boiled. It is possible to cool the resulting mash, then drain it into a fine mesh basket. The filtrate thus obtained is made to stand overnight or until a slightly sour taste is assumed, after which it is cooked into a concentrate. The cooled concentrate is applied to a starter from the previous brew, which is again permitted to ferment overnight. The substance thus obtained, Pito, is a dark brown liquid that ranges from sweet to bitter in taste. It contains lactic acid, amino acids, sugars and has a 3 percent alcohol content.
Merissa
This is an alcoholic beverage that is consumed commonly in Sudan. In a relatively complex process, it is prepared from sorghum and millet. Brewing takes place in three main stages (i) ‘ajeen’ fermentation, a lactic souring of sorghum, (ii) ‘debosa’ fermentation, a starter activating phase and (iii) merissa fermentation, an alcoholic fermentation.
Bouza
Bouza, an alcoholic beverage made from wheat in Egypt, has been known to the Egyptians since the days of the Pharaohs. It is a thick, pasty yellow drink with a good taste which creates a feeling of warmth when consumed. It is prepared by grinding the wheat grains, putting a part of them (3/4) in a wooden reservoir and kneading them with water into a dough. The dough is sliced into thick, very lightly baked loaves. Meanwhile, the remaining grains (approximately 1⁄4 of the total volume of wheat grain) are moistened with water, sprinkled for 3-5 days, sun-dried, ground and mixed with bread crumbs soaked in water in a wooden barrel. Bouza from the previous brew is added as an inoculum. The mixture is allowed to ferment at room temperature for a duration of 24 hours, during which the liquid is sieved to extract large particles and diluted with water to the desired consistency.
Like most opaque beers, bouza has a very short shelf life and is supposed to be consumed within a day. Its pH is increased to between 3.9 and 4.0 and its alcoholic content is increased to between 3.8 and 4.2 per cent within a 24-hour cycle.
