Fermentation is a metabolic process that consumes sugar in the absence of oxygen. The products are organic acids, gases, or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. The science of fermentation is known as zymology.
Fermentation in food processing is the process of converting carbohydrates to alcohol or organic acids using microorganisms—yeasts or bacteria—under anaerobic conditions. Fermentation usually implies that the action of microorganisms is desired.
Fermentation in Dairy Foods
Milk has been used to produce fermented milk products as far back as 10,000 B.C. in different regions all over the world. The many benefits of fermented milk products include enhanced digestibility, new and unique flavours, added probiotics, vitamins and minerals, and preservation products for a food that normally has a very short shelf life.
Fermenting Process
The processes used to turn milk into different fermented foods involves adding lactic-acid-producing microorganisms, such as bacteria and yeast, which ingest lactose, or milk sugar, and release lactic acid as waste. This result is a rise in milk acidity, which allows the production of kefir, yogurt, cheese and sour cream among other fermented foods.
Kefir
Kefir is a fermented yoghurt-like drink that dates back centuries to the shepherds of the Caucasus Mountains. The word “kefir” is derived from the Turkish word “Keif,” which means “good feeling”; a benefit this drink is said to provide for those who consume it. Kefir is produced with starter grains, known as kefir grains, which contain active microorganisms consisting of 83 to 90 percent lactic acid bacteria and 10 to 17 percent yeast. Kefir incorporates various essential vitamins, minerals, amino acids and enzymes, particularly phosphorus, magnesium, calcium and vitamins B2, B12, D, K and A.
Yogurt
A staple of the Middle Eastern diet for thousands of years, yoghurt is a fermented food that holds the same level of protein and fat as the milk from which it is produced. It is also a source of calcium and vitamins B2, B6 and B12. Yogurt, like other fermented milk products, is primarily cultured from cows milk but can be made from goat’s milk. Microorganisms can also be used to ferment non-dairy milk, including coconut milk, almond milk and soy milk, into yoghurt.
Cheeses
Cheese may be the most popular fermented milk product, using more than one-third of all milk produced in the United States each year for its production. Both soft and hard types of cheeses are produced by culturing milk for an extended period of time. Certain types of cheeses can be made simply by straining the moisture out of sour cream or yogurt. Some other types of cheese, however, require additional steps in the culturing and fermentation process. Over 2,000 varieties of cheeses exist, with some of the most notable being cheddar, feta, cream, goat and blue.
Sour Cream
The original process for making sour cream was to simply let cream sour on its own. Today, a more proactive process is used: the lactic-acid-producing bacteria Streptococcus lactis. The flavour of sour cream is mild and tangy and the texture is thick and smooth. With a fat content somewhere between 10 to 14 percent, sour cream has significantly fewer calories than mayonnaise – a food sour cream can replace in many applications. Sour cream also works well in baking recipes for cookies cakes, bread and pies.
Fermentation in Vegetables
Fermented vegetables begins with Lacto-fermentation, a method of food preservation that also enhances the nutrient content of the food. The action of the bacteria makes the minerals in cultured foods more readily available to the body. The bacteria also produce vitamins and enzymes that are beneficial for digestion.
In eastern Himalayan regions of India, a wide range of fermented vegetable products are prepared for bioprocessing the perishable vegetable for storage and further consumption. Lactic acid fermentation vegetables such as gundruk, sinki, and khalpi are fermented vegetable products of Nepal, Sikkim, and Bhutan.
Fermentation in Indian Foods
India is traditionally rich in fermented foods. In the Indian sub-continent, fermented food using local food crops and other biological resources are very common.
Fermented foods such as idli and dahi were described as early as 700 BC. At present, there are hundreds of fermented foods with different base materials and preparation methodology. Each fermented food is associated with a unique group of microbiota, which increases the level of proteins, vitamins, essential amino acids and fatty acids
Foods like idlis, dosas, dhoklas, wadas and kadhi are some of the lactobacillus fermented cereals and legumes that are commonly consumed in India. The fermented foods increase the absorption of vital minerals from the gastrointestinal tract, thus preventing mineral deficiencies. Bread, fish sauce, wine and beer are some of the yeast-based fermented food beverages.
Examples of some Indian fermented foods:-
| Fermented food | Ingredients | Place of origin | Related Microorganisms |
| Rabdi (rabadi) | Flour of barley, pearl millet, corn or soybean and country buttermilk | Rajasthan | Bacillus and Micrococcus sp. |
| Kulu | Wheat flour, buttermilk | Himachal Pradesh | Lactobacillus sp. |
| Idli | Rice, black gram dhal, table salt, fenugreek seeds | South India | L. mesenteroides, E. faecalis, P. cerevisiae |
| Dosa | Rice, black gram dhal (either raw or parboiled rice), table salt | South India | L. mesenteroides, E. faecalis |
| Dhokla | Bengal gram dhal, rice and leafy vegetables | Gujrat | L. fermentum, L. mesenteroides, E. faecalis |
| Chilra or lwar | Wheat/barley, buckwheat flour and starter material Treh | North India | Not reported |
| Sinki | Radish root | North-east India | L. casei, L. brevis, L. plantarum, L. fallax, L. fermentum |
| Kinema | Soybeans | Darjeeling, Sikkim | E. faecium |
| Kanji | Carrot or beet root, rice, mustard | North India | L. pentosus, L. paraplantarum, L. plantarum |
| Curd (Dahi) | Milk | India | S. cremoris, S. lactis, S.thermophilus, L. bulgaricus, L. acidophilus, L. helveticus, L. cremoris, , Lactobacillus delbrueckii subsp. indicus |
| Gundruk | Leaves of mustard/radish/cauliflower | Arunachal Pradesh | P. pentasaceous, L. fermentum, L. casei |
Indian fermented foods are consumed by the local population not just as a diet but as traditional medicine too. Many of the foods were observed to have a beneficial effect during ailment by the local people and they are used as a special diet or medicine for ages. Fermented food idli is easily digested and often used as food for infant and invalids. Fermented milk dahi can be used to cure intestinal disease such as diarrhoea; intake of dahi has anti-cholesteric, anticarcinogenic, anti-diabetic, angiotensin-converting enzyme inhibition effect and anti-atopic dermatitis effect.
Fermentation in Bakery Products
Fermentation is a baking process in which yeasted dough rises and increases in volume and flavour is developed. Fermentation occurs when yeast converts sugar present in flour such as starch into carbon dioxide and ethyl alcohol. CO2 gas is trapped by gluten proteins the flour which causes the dough to rise. Fermentation results in a light and airy crumb.
Fermentation influences product volume, shape, crust colour, and crumb cell structure.
Fermentation in Alcoholic Beverages
Fermented beverages are produced through the process of fermentation. Fermentation in the case of alcoholic beverages refers to a metabolic process by which yeast converts sugar to ethanol. Yeast is a type of fungus used in the fermentation of alcohol. In order for fermentation to take place, you begin with some type of carbohydrate that is needed to feed the yeast. The type of carbohydrate used determines what the final product will be.
Let’s look at some examples. Beer is produced by fermenting grain. Wine or hard cider is produced by fermenting fruit. Mead is produced by fermenting honey. Milk and tree or plant sap can be used to produce fermented beverages as well.
There is a limit to the alcoholic content of fermented beverages because yeast cannot survive in alcohol. Once the concentration of ethanol produced by the fermentation process reaches about 15%, the yeast will die and fermentation process will end.
In order to produce beverages above the concentration of ethanol achieved through fermentation, a distillation process is used. Distillation of alcoholic beverages is the process by which water is removed from a mixture of ethanol and water.
