What Is Fermentation?
Fermentation is any metabolic process in which microorganisms’ activity creates a change in food and beverages. This can result in enhancing flavour, preserving or providing health benefits. Fermentation promotes the growth and life cycle of good bacteria to transform the flavour and extend the shelf life of ingredients.
Historically fermentation techniques were used as a way of preserving food and drinks long before the days of refrigeration. During the process of fermentation, microorganisms such as bacteria, yeast or fungi convert organic compounds (such as sugars and starch) into alcohol or acids. For example, starches and sugars in vegetables are converted to lactic acid and this is what acts as a natural preservative. Fermentation can produce quite distinctive, strong & slightly sour flavours.
Science!
There’s a lot that happens behind this chemical process. Here’s a few key points to help you understand the science behind fermentation.
- Microorganisms feed on carbohydrates & sugars for energy and fuel. Organic chemicals deliver that energy various cells when needed.
- Fermentation is similar to anaerobic respiration, the kind that takes place when there isn’t oxygen present.
- When there’s enough oxygen present, aerobic respiration occurs.
- Depending on environmental conditions, individual cells and microbes have the ability to switch between the two different modes.
- Fermentation produces lactic acid and/or alcohol.
What Happens During The Fermentation Process?
Fermentation occurs in the absence of oxygen, and in the presence of beneficial microorganisms (yeasts, moulds, and bacteria). During fermentation, these microbes break down sugars and starches and turn them into alcohols and acids, making food more nutritious. They also act as a preservative, giving the ability to store food and drink for longer periods of time without spoiling.
All vegetables are covered in the good bacteria ‘lactobacillus’. When you slice up, grate and squeeze them with salt, they release juice which mingles with the salt to create a brine. Once contained within this briny ecosystem, lactobacillus multiplies and begins to break down the ingredient. It digests the natural sugars and transforms into lactic acid, which creates a tangy flavour and sour environment that keeps the growth of nasty bacteria at bay.
Many people are cottoning on to the appeal of naturally fermented food. It’s becoming less scary, and something we increasingly want to do for ourselves at home, rather than relying on industrial versions. Many of these have been pasteurised and therefore no longer ‘alive’, or as healthy or flavourful. Beginning with fruit and vegetables is a good introduction.
Common Types Of Fermentation
Lactic Acid Fermentation - Yeast strains and bacteria convert starches or sugars into lactic acid, requiring no heat in preparation. Lactic acid bacteria are vital to producing and preserving inexpensive, wholesome foods. This method makes sauerkraut, pickles, yogurt, kimchi and sourdough bread.
Ethanol/Alcohol Fermentation - Yeasts break down pyruvate molecules in starches/sugars to produce alcohol and carbon dioxide molecules. Alcoholic fermentation produces wine and beer.
Acetic Acid Fermentation - Starches and sugars from grains and fruit ferment into sour tasting vinegar and condiments. Examples include apple cider vinegar, wine vinegar, and kombucha.
Stages Of Fermentation
Primary fermentation - In this brief phase, microbes begin working on raw ingredients such as fruit, vegetables, or dairy. The microbes present in the surrounding liquid (such as brine for fermented vegetables) prevent putrefying bacteria from colonising the food instead. Yeasts or other microbes convert carbohydrates into other substances such as alcohols and acids.
Secondary fermentation - This longer stage of fermentation lasts several days or even weeks. Alcohol levels rise and yeasts and microbes die off and their available food source (the carbohydrates) becomes scarcer. Winemakers and brewers use secondary fermentation to create their alcoholic beverages.
Tips For Beginners
Establish Your ‘Starter’ Cultures - Microbes are naturally present in the air you breathe, but to begin fermentation you will often need a ‘starter’ culture, such as whey (from yogurt), a SCOBY for kombucha (Symbiotic Colony of Bacteria and Yeast), or even liquid from a previous ferment. Starter cultures are already rich with beneficial microorganisms. When you add them to your food or beverage product, they’ll multiply rapidly and jump-start the fermentation process.
Keep Your Equipment Clean - To prevent bad bacteria from leaching onto your ferment, it’s essential that you clean and sterilise your kitchen equipment (especially jars) and the surfaces that you work on.
Avoid Exposure - Exposing your ferment to air can prevent proper fermentation from taking place and increase the risk of spoilage. To prevent fermenting food from coming into contact with air, you can submerge it in a brine (salt solution). When fermenting solid pieces of food like chopped vegetables, this method works well.
Storage - To avoid air contamination, you should keep your ferments in a sealable storage container. At home you can use a simple jar and lid to lock out air. If you’re committed to monitoring your ferment so it doesn’t spoil, you’ll need to manually to release the carbon dioxide produced (this is called ‘burping’). Fermentation crocks on the other hand, have a valve to vent gases released during fermentation.
Fermentation Management - By controlling the temperature of the environment, you can affect the outcome of your fermentation. Typically, microbes work well when their environment is warm or room temperature, but the ideal temperature depends upon the type of microbes you’re using and what you’re fermenting. Altering the temperature can impact your process greatly. Moving your product to a cooler environment, such as a basement or a refrigerator, will slow the rate of fermentation. Heating a ferment, on the other hand, can kill your essential microbes.
Select & Store
Keep fermented foods in the fridge and beware of buying those straight from the shelf at a supermarket. If it’s not in the fridge, it’s more than likely been heat treated (pasteurised) which destroys the naturally occurring probiotics. Watch your choice of yogurts and kombucha too. Those packed with sugar, high fructose corn syrup or artificial sweeteners are not going to support the gut as much as natural, live options.
Pickled vs Fermented
There’s often confusion over the difference between pickled foods and fermented ones. Pickles, like the ones you buy in the supermarket, are preserved in an acidic liquid, typically vinegar. Although vinegar is a product of fermentation the pickles themselves are not fermented, and so do not offer the same health benefits of fermented vegetables.
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