Fermentation processes are broadly divided into two parts viz: liquid fermentation and solid fermentation. In liquid fermentation, the microbial cells are suspended in an aqueous nutrient medium. But in solid fermentation, the microbial cells are adsorbed to a solid and nutrient rich material that supports the growth of the organism.

The volume of free liquid or aqueous medium is minimal in solid fermentation processes unlike in liquid fermentation processes where the free liquid is large. Fermentation occurs when microbes including yeasts, actinomycetes, moulds and bacteria consume, breakdown or metabolize organic substrate molecules as part of their own metabolic process; and in the process produce desired end-products or metabolites that are of great economic importance.

The growth of microbes in food is considered a problem especially when such microbial activities result in disease outbreak (as is obtainable in food borne diseases) and food spoilage. Nevertheless, some fermentative processes spurred by microbial activities are important to man, animals and the environment because they result in the production of desirable end-products including fermented foods, beverages, drugs and alcohols.

These fermentative activities are usually carried out in bioreactors that support the growth of microbes via nutrient supplementation or addition. Fermentation processes are usually classified according to the ways or manner in which the substrate or fermentation nutrients are added and the desired end-product recovered or harvested from the process.

To this end, there are usually different types of fermentation processes used in industrial/biotechnological productions especially those industrial processes that has to do with the production of foods, alcoholic beverages, drugs and pharmaceutical products. Batch fermentation, fed-batch fermentation, continuous fermentation and semi-continuous fermentation are usually the major types of liquid fermentation processes used in industrial microbiology productions.

SIGNIFICANCE OF FERMENTATION

• Fermentation increases the shelf-life of a finished product.

• It improves the varieties of tastes and flavours of finished products.

• It improves the nutritional value of foods and beverages.

• It decreases the toxicity of finished products.

• It improves the therapeutic value of finished products. For example, some fermented products such as yoghurts contain some beneficial microbes that improve the health status of the gut flora; and this goes a long way in improving the general health of the body.

• Fermentation increases digestibility in the host when fermented finished foods are consumed.

• Fermentation processes produce substances such as acids and alcohols that inhibit the overgrowth of spoilage and pathogenic microbes in the food.

• Fermentation processes produce industrially useful end-products such as organic acids, alcohols, citric acid, alkaloids, aldehydes and ketones that are used for the production of other important products. For example, citric acid is used in the food industry, in medicine, in pharmacy and in various other industries. It is used in the food industry for example, as a major food acidulant used in the manufacture of soft drinks and sweets. It is used in medicine as sodium citrate in blood transfusion to prevent blood clotting. Citric acid has a low pH, and thus it is used in hair rinses, after shave lotions and in wig setting fluids.  

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