Let’s harness, upgrade indigenous food fermentation technologies

Fermented foods contribute to about one-third of the diet worldwide, and cereals are particularly important substrates for fermented foods around the globe

SEVERAL fermented foods are produced at household level in Zimbabwe. However, with the exception of amasi, limited work has been done to study these foods with a view to upgrading their traditional technologies. The current industrially produced foods and beverages are only simulations of the traditional products as either different substrates such as sorghum malt are used instead of millet malt (chibuku) or starter cultures developed elsewhere are used for the fermentation (lacto) or unfamiliar ingredients such as soy protein (mahewu) are added.

Products include fermented maize porridges (mutwiwa and ilambazi lokubilisa) fermented milk products (mukaka wakakora/amasi and hodzeko) non-alcoholic cereal-based beverages (mahewu, tobwa and mangisi) alcoholic beverages from sorghum or millet malt (doro/uthwala and chikokivana) distilled spirits (kachasu) and fermented fruit mashes (makumbi). Mahewu (amahewu) is a beverage, which is from either thin maize porridge or thick maize porridge (sadza). It is an adult-type food, which is commonly used to wean children and is introduced to infant between 4–18 months.

The maize is mixed with water or if thick (sadza) is mashed and mixed with water. Sorghum or millet malt or wheat flour is added to either mix or left to ferment.

Tobwa is another non-alcoholic cereal-based beverage, which is very similar to mahewu but has not been previously documented. Like mahewu, it is made by mashing left over sadza into small pieces and mixing it with water to form a slurry, then leaving the mixture to ferment overnight.

The only difference with mahewu is that no malt is added to the fermentation thus making the process a totally lactic acid fermentation. Tobwa is usually drunk by those people whose religion does not allow them to drink beverages to which malt has been added. Mangisi is a sweet-sour beverage made from the natural fermentation of millet mash.

The preparation varies in the different regions of Zimbabwe. In one variation, finger millet is malted then milled and the flour mixed with water. The mixture is slowly heated for 80 minutes to almost boiling point. The resulting product is the mash which is cooled, diluted, strained and allowed to stand for some hours during which spontaneous fermentation takes place to give mangisi. Another variation involves malting the finger millet, milling, mixing the flour with water and boiling the mixture for 1–2 hours.

The masvusvu is cooled, diluted and allowed to stand overnight. On the second day more malt flour is added and the mixture left to ferment until early on the third day when the coarse solids are strained off and the fermenting mixture returned to the fermentation vessel. The mangisi is ready for consumption later on the same morning of the third day.

Mutwiwa or mudzvurwa is a sour maize meal which can be used to produce sour sadza. Dried maize grains are sprinkled with a little water, pounded with a pestle and mortar to remove their husks, then sundried and winnowed. The dehulled grains are washed, steeped in clean water and left to ferment until gas production ceases. The fermented dehulled maize is then either wet milled by pounding, winnowed and the fine meal sun-dried or dried and hammer-milled into maize meal.

The product, mutwiwa, is then used to prepare thin porridge or sadza, which has an improved lactic acid taste. Ilambazi lokubilisa is a fermented thin sour porridge, which is similar to porridge produced from mutwiwa although in this case the maize is fermented after milling. It is consumed widely in Zimbabwe and used as a weaning food. Maize meal is thoroughly mixed with a little amount of water and allowed to ferment in a closed vessel for about 2–4 days. The fermented meal is then used to make ilambazi lokubilisa/sour porridge.

Makumbi is the generic name for beverages made from wild fruits. Wines can be made from marula plant (Scleroecarya caffra, mapfura/umkumbi); sand apple (Parinari curatellifolia; muhacha); murara/ilala tree (Hvphaene benguellensis); buffalo thorn (Ziziphus mauritiana, musau); monkey orange (Strychnos spinosa mutamba); donkey berries (Grewia monticola; mutongoro/umtewa; G flavescens, mubhubhunu/ubhuzu), monkey fingers (Popowia obovata, munyani/umkozombo), torchwood (Balanites aegyptiaca, nyahoko), bird plum (Berchemia discolor, munyii/umcaga), plum (Bequaertiodendron magalismontanum, muhorongwa/ umhlautshwa), monkey pod (petersiana, muremberembe), jackal berry (Diospyrosme spiliformis, mushenje/umdlawuzo), granite cinia (Garcinia huillensis, mutunduru), wild plum (Harpephyllum caffrum), indaba tree (Pappea capensis, chitununu/uzagogwane; tenuinervis, mudzambuya/umkungu) and water berry (Syzygium cordatum, mukute/ umdoni). These makumbi products can also be improved through microbiological and other associated research .

Vinegar can be made from apples and pine apples. For pine apples it is noted that in preparing peeled pineapples a considerable amount of waste can be generated. This waste is mainly composed of the peel and some parts of the fruit itself. Placing the peelings and waste fruit in containers of water and adding sugar and yeast and letting it sit for about eight days will provide vinegar. The vinegar is of a distinct, light pineapple flavour and can be used in the same way as other vinegars.

Many Zimbabweans have not given thought to making wine from mangoes. For fresh mango marketing the shape and size of the fruits are important. Thus fruits which cannot be marketed as a result of shape and size can be used for producing mango wine. Poor quality raw materials for making the wine will result in poor quality wine that can also be unsafe. Mangoes needed for wine production should not be over ripened, free of mould and rot and not badly damaged. Mangoes need to be peeled and cut prior to pulping.

Fruits are pulped and then the juice is filtered using a strainer. If sugar content of the juice is too low then sugar can be added. Then the juice is placed in a vessel (made from plastic, wood or stainless steel) for fermentation with a yeast inoculation for five to 21 days. The vessel is fitted with an airlock. After initial fermentation the juice is transferred to a larger airtight vessel and then the wine is filtered and funnelled into sterilised bottles and capped for maturing.

The mango wine can be aged, but checks need to made on quality and detect any problems with the “instability” of the wine.

Zimbabweans especially those from Manicaland eat cassava and madhumbe but have never given thought to the fact that fermentation is used to remove cyanide poison form the plant. Cassava contains a naturally occurring chemical: cyanogenic glucoside, and when eaten raw or improperly processed, this substance releases potentially fatal cyanide into the body, but correct processing can remove it.

The cassava is first peeled (as about 60-70 percent of the poison is in the peel) and then soaked in stagnant water or fermented in sacks for about three days. It is sometimes grated or rasped as this helps to speed up the fermentation process. At the beginning of the fermentation, Geotricum candida acts on the cassava, tending to make the product acidic, which finally kills off the micro-organisms as they cannot exist in such a medium.

A second strain of microorganisms (Cornibacterium lactii), which can tolerate the acidic environment then take over and by the third day 90-95 percent of the dangerous chemical will have been hydrolysed.

The cassava also develops its characteristic flavour. The product is then sieved and the fine starch particles are fried in an iron pan alone over a flame or with some vegetable oil. During this process most, if not all the remaining toxins are given off. The liquor from a previous fermentation is used as a starter, thereby reducing the period of fermentation to about 6-8 hours.

Few Zimbabweans are aware that beer can be made from bananas. Banana beer is a weak alcoholic beverage popular throughout Africa, and is made by fermenting bananas with cereal flour - often sorghum flour. It is sweet and slightly hazy with a shelf-life of several days under correct storage conditions.

In Kenya, banana beer is known as urwaga, and in Uganda lubisi. Ripe bananas (Musa species) are used as they have a high sugar content which is necessary for fermentation. Preparation involves extracting the juice from peeled bananas, which are unspoiled by micro-organisms or other contaminants.

Clean boiled water is added to the extracted juice to dilute the banana juice so that the concentration of soluble solids is low enough for the yeast to ferment the juice. Grinded cereal (sorghum or millet) is lightly roasted over an open fire and then added to the diluted banana juice in a clean bucket.

The bucket is covered with a clean lid, and left in a warm place to ferment for 18 to 24 hours. The ground cereal improves the colour and flavour of the beer. After fermentation the beer is filtered through a cotton cloth, sterilised with boiling water. Packaging is usually only required to keep the product for its relatively short shelf-life and clean glass or plastic bottles can be used. The product is stored in a cool place away from direct sunlight.

As banana beer is made from raw material that does not undergo any heating or cooking at any stage of the process, the pulp is an excellent substrate for microbial growth both of the desirable yeasts and the non-desirable spoilage bacteria. The fermentation is brought about by natural yeasts that are present on the banana. Heating or boiling the raw material would kill these natural yeasts and spoil the traditional flavour of the beer. This implies, for important public health and marketing that it is essential that strict attention is paid to cleanliness of the equipment and processing area and to personal hygiene to avoid contamination of the beer with other bacteria that may form acid rather than alcohol.

Equipment needs to be sterilised prior to use with boiling rather than chlorinated water, which can affect the fermentation.

Nutritional value

Fermented foods contribute to about onethird of the diet worldwide, and cereals are particularly important substrates for fermented foods around the globe. Fermentation of both cereals and fruits and vegetables, can make otherwise inedible food stuffs safe, nutritious, and palatable, improving digestibility of protein and carbohydrates, removing natural toxins, and decreased cooking times. Specifically, lactic acid fermented foods are the traditional means for weaning infants in many developing countries, as they improve both food safety and digestibility.

By acidifying porridges with lactic acid fermentation, starch is hydrolysed into shorter chains of glucose and dextrose, which reduce the viscosity of the porridge and increase its energy density, helping the child to better meet its energy requirements (FAO).

Anti-nutritive compounds: Cereal-based diets, including maize, sorghum and millet, contain a number of anti-nutritive factors, including reduced availability of minerals, including calcium, iron, magnesium and zinc, as well as deficiencies in essential amino acids including lysine, tryptophane and methionine, which serve as building blocks for proteins. Other anti-nutritive components typical of cereal and legume foods include acids and tannins which can further reduce mineral availability, and further exacerbate malnutrition.

However, fermentation may serve to improve the nutritional value and protein quality of food staples, by inactivating naturally occurring toxins, as with cassava.

Essential steps in traditional household-level processing, such as soaking, germination and fermentation, may help reduce these anti-nutritive compounds.

Factors hampering the development of fermented foods

The production of fermented foods is still largely a traditional family art done in homes in a crude manner. Consequently the production has not increased substantially more than a cottage industry. Many of them are gradually acquiring label of food for the poor population or associated with low incomes. Amongst the various factors working against traditional fermented foods the following appear generally valid:

◆ Inadequate raw material grading and cleaning contributing to the presence of foreign matter (such as insects, stones) in final product.

◆ Crude handling and processing techniques employed.

◆ Lack of durability (shelf life).

◆ Lack of homogeneity.

◆ Unattractive presentation. Inadequate presentations inhibit consumers from becoming regular purchasers. Among the factors that may be working against fermented foods is the increasing popularity of food introduced from western countries. Nevertheless, demand for locally processed foods is bound to increase as the imported counterparts are expensive. The factors outlined here serves as a general guideline to some major goals in the exercise of improving the present status of fermented foods.

◆ Eng Perkins Muredzi is the Dean in the School of Industrial Sciences and Technology at the Harare Institute of Technology and can be contacted on perkinsmuredzi@yahoo.co.uk