Lactic Acid Fermentations

Lactic acid fermentations are among the most ancient and important fermentations in the world: they enabled the human race to survive and thrive and they remain very important in the diets of humans today (4).

Lactic acid fermentations became known to humans as soon as they started domesticating and milking cows, sheep, and goats. People had to store the milk in a container, and one of the earliest containers was the stomachs of slaughtered animals. Milk sours very rapidly because of its natural content of lactic acid bacteria. Sour milk became one of the first fermented foods after humans settled down and became agriculturists, and it lives on in the form of yogurts today. Stored in animal stomachs, the sour milk curdled, lost its whey, and became primitive cheeses through the activities of other lactic microorganisms in the environment. For millennia, cheeses have been an important part of the diet of humans and they remain so today.

Lactic acid fermentations are very energy efficient, generally requiring no heating or cooking either before or after fermentation. A prime example of lactic acid vegetable fermentations is the sauerkraut fermentation. Fresh cabbage is shredded and mixed with 2.25% w/w salt (sodium chloride). The salted cabbage is placed in a crock and covered with a lid or a plastic cover that allows no penetration of air. The natural fermentation (no inoculum required) begins with the development of Leuconostoc mesenteroides. L. mesen-teroides produces both lactic acid and carbon dioxide, which flushes out any residual oxygen, helping to maintain anaerobic conditions. The second organism that develops is Lactobacillus brevis, which produces additional lactic acid and carbon dioxide. This is followed by Lactobacillus plantarum, which produces additional acid. The last organism to develop is Pediococcus cerevisiae, which produces additional acid. The final product has an acidity of about 1.7% to 2.3% acid (as lactic) and has excellent keeping quality as long as the product is kept anaerobic. The sauerkraut can be eaten fresh without cooking as a salad or cooked as a hot food.

Another lactic acid fermentation is that of Korean kimchi, which is a staple in the diet of the average Korean, who may eat 100 g a day in summer and 150 g a day in the winter. In Korean kimchi, Chinese cabbage is a prime substrate but radishes, red peppers, and other vegetables may be included. The vegetables are shredded and immersed in a strong salt brine (5-7% salt for 12 hours or 15% salt for 3-7 hours) followed by draining and rinsing. The subsequent fermentation time depends on the temperature of fermentation (one day at 30 °C or 3-60 days at 5°C). Kimchi is less acidic than sauerkraut and the product is carbonated.

Lactic acid fermentation has been applied to most vegetables such as cucumbers and carrots, and some green fruits, such as limes and olives. It has been utilized by Indian farmers to preserve excess vegetables during the growing season. Lactic acid fermentation is utilized throughout the world as a prime method of preserving fresh vegetables.

It is likely that bread fermentations began as soon as humans started to use fire/ cooking and grinding starchy grains such as barley, wheat, millet, rye, and sorghum to make them more easily consumed. Such flours slurried with water, immediately begin to ferment by lactic acid organisms and yeasts in the environment. These microorganisms struggle for survival in the increasingly acidic mixture. The outcome generally includes one or more lactic acid species and one or more yeasts. If the flour-water slurry is dense enough to form a dough or pancake-like structure and it is baked, it will yield, depending on the conditions, leavened or sourdough-like breads. Since at least 5000 B.C., breads have played a significant role in human diets. Wheat flours contain gluten, which retains the carbon dioxide produced by heterofermentative lactic acid bacteria and yeasts fermenting symbiotically.

Rice does not contain gluten, so it cannot yield leavened bread, but people from the region known today as India discovered a way of producing bread-like foods from rice by combining fermentation of rice with that of legumes such as black gram. Both ingredients are soaked in water and then ground in a mortar to make a stiff batter that when incubated overnight is leavened (rises) so that it can be steamed (Indian idli) or cooked as a pancake (Indian dosa) adding leavened bread-like products to the Indian diet (4).

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