Lactic acid fermentation is used intentionally by humans for thousands of years. A common method of preservation, this biological process relies on the power of microbes such as probiotics to create popular food and drinks.
In lactic acid fermentation, sugars like glucose are converted without oxygen into cell energy and lactic acid. Anaerobic fermenting depends on lactic acid bacteria (LAB) to consume sugars and turn them into lactic acid.
This process also happens in the human body to increase muscle performance with a temporary infusion of energy. It can cause "muscle burn" or acidosis if too much acid accumulates.
Lactic acid and its relative, lactate, differ from lactose. Lactose is the sugar present in dairy products, also called milk sugar. Lactate is lactic acid with an extra hydrogen atom.
People with lactose intolerance can eat foods made with or containing lactic acid, including bread, green beans and salami. It's called "lactic" only because it's first isolated from milk, in 1780.
Lactic Acid Bacteria
Lactic acid bacteria (LAB) live on plants, in milk, and in animal digestive systems. They're anaerobic, ie they don't need oxygen. Fermentation often happens in sealed or submerged conditions.
Common lactic acid bacteria (LAB) include Lactobacillus, Streptococcus, and Leuconostoc. These ferment food and enhance its flavor, texture and nutritional content. LAB are found naturally on leaves, fruits and vegetables.
The Chemical Magic: Breaking Down Sugars
Fermentation begins when LAB are given food containing sugars, primarily carbohydrates. Instead of using oxygen to break down the sugars for energy, LAB use a different metabolic pathway.
Conversion of sugars like glucose, fructose, and lactose into lactic acid also lowers pH of the environment, making it more acidic. Acidity is a natural preservative and inhibits or slows down yeast and other microbial activity.
Why Acidity Matters
By lowering pH, lactic acid effectively creates an environment hostile to spoilage organisms like Salmonella. Food can be stored for longer periods without the modern convenience of refrigeration.
Fermented food has strong nutritional benefits as the body absorbs nutrients more efficiently. Uptake of B vitamins, vitamin K, and essential amino acids increases.
Eating fermented foods introduces probiotics into the body. These beneficial bacteria support gastrointestinal (GI) wellness. Probiotics can fortify the immune system and are linked to better mental health.
Flavor and Texture Transformation
Beyond its preservative abilities, lactic acid fermentation also significantly affects flavor and texture of foods. The lactic acid itself is responsible for the characteristic sour or tangy notes.
Metabolic activities of LAB create a range of flavorful compounds. These include esters, aldehydes and alcohols, contributing to complexity and depth of flavor in the finished foods.
In milk, lactic acid causes proteins to coagulate, causing the creaminess of yogurt and cheese, production of whey. In vegetables like cabbage, fermentation softens tough fibers into tender and easily digested nutrition.
Basics of LAB Fermentation
Preparation: Salt added to food, such as green beans, draws out moisture and creates an environment to repel unwanted bacteria. Salt also inhibits growth of yeast, a steadfast companion of LAB.
Inoculation: The lactic acid bacteria on or in the veg start to multiply. For artisan or industrial production, or for quicker gratification, a starter culture may be introduced to increase bacterial activity.
Fermentation: Store the mixture in a sealed container at room temperature. Over a few days to weeks, the bacteria consume sugars and produce lactic acid and other compounds.
Gas released during lactic acid fermentation, or temperature fluctuations, can cause jars to explode if sealed too tightly. Exploding jars have been attributed to poltergeist activity.
Storage: After fermentation, move the food to a cooler area, like the fridge or a root cellar, to slow down the process. This preserves the food and allows flavors to mellow and mature.
The above is an overview. There are many recipes / methods available online for fermenting various foods with lactic acid bacteria. Have fun.
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