lactic acid fermentation

Introduction to Fermentation and Home Culturing

In its broadest sense, fermentation refers to a living process by which microorganisms convert sugars into acids, alcohols and gases under anaerobic or minimally aerobic conditions. The three most common types of fermentation are lactic acid fermentation, ethyl alcohol fermentation and acetic acid fermentation by lactic acid bacteria, yeasts and acetobacter bacteria respectively. I like to use the word ‘culture’ as a noun and verb to refer to the art and science of home fermentation under carefully controlled conditions. Cultured foods are not culinary novelties but steeped in 12,000 years of anthropological history since the paleolithic period, used as a form of natural food preservation for the excess harvest. Although now with the convenience of supermarkets and readily available fresh food, it is good and fun to practice home fermentation, not least because of the numerous health benefits. This page will focus largely on lactic acid fermentation, the process responsible for sauerkraut, kimchi, yogurt, nut or seed cheeses and fermented drinks including rejuvelac.

Health Benefits of Fermented Foods

Fermented products have increased amounts of vitamins and minerals, including B vitamins, riboflavin, folate, pyroxidine, and biotin. Some bacteria, including lactic acid bacteria, are able to excrete small amounts of these vitamins into the surrounding medium. Vegetarians, vegans and the elderly are at higher risk of developing B12 deficiency, and fermented foods may provide a source of this important nutrient. The anaerobic environment of fermentation also preserves the vitamin C content of foods.

Fermented products provide a good source of readily assimilable, less allergenic nutrients. Much of the macromolecules are pre-digested or broken down by lactic acid bacteria during fermentation: gluten in grains, lactose in dairy and starch and in starchy foods such as beans and vegetables. The predigestion of macromolecules to other compounds allows some gluten-sensitive people and lactose-intolerant people to tolerate fermented bread and yogurt respectively.

Fermentation helps to reduce phytic acid, allowing the body to absorb more minerals. Phytic acid is found in the outer hull of grains, nuts, seeds and legumes and chelates divalent minerals such as zinc, calcium, iron and magnesium in the gut. A diet high in phytic acid may lead to mineral deficiencies. To learn more about phytic acid, read this article. A study of brown rice shows that fermentation was capable and most effective in reducing phytic acid levels (56–96% removal) compared to just soaking or steeping only.

Fermented foods provide a direct and rich source of probiotics and enzymes. Etymologically the term probiotics is derived from the Greek “probios” which means “for life”. Today it is defined by the Food and Agriculture Organization / World Health Organization as live microorganisms that confer health benefits on the host when taken in adequate amounts. Probiotics can colonize the gastrointestinal tract and help to maintain healthy intestinal flora by greatly increasing the numbers of beneficial microorganisms. Probiotics also produce numerous anti-biotic, anti-tumor, anti-viral, and anti-fungal substances, and is being studied as an alternative solution to antibiotics in view of the increasing spread of antibiotic resistance. Importantly, note that the benefits of probiotics, as “living foods,” can only be reaped in the raw state, as cooking and heat destroys the bacteria.

Choosing The Best Ingredients: Produce, Salt, Starters, Water and Boosters

There are three basic ingredients necessary for lactic acid fermentation: fresh produce (vegetables, fruits or grains), salt, water and an optional starter culture.

Use the freshest produce, preferably S.L.O. (seasonal, local, organic). You won’t get the best results with ingredients that are past their prime.

Salt for Vegetable Ferments
Lactic acid fermentation of fruits and vegetables is almost always carried out in a salted medium or brine. The purposes and actions of of salt are manifold: to soften the ingredient by plasmolysis; to create anaerobic conditions around the submerged product through formation of a liquid phase; to provide a source of minerals to support the growth of mineral-hungry lactic acid bacteria; to promote the growth of lactic acid bacteria over spoilage bacteria while inhibiting pectinolytic and proteolytic enzymes that cause further vegetable softening and putrefaction; and to strengthen pectin that holds vegetable cells together (as such using more salt renders a crunchier texture). If you are watching your sodium or prefer a less salty ferment like I do, low-sodium fermentation is tricky but not unimpossible. One option is to use starter cultures such as kefir grains to jump start acid production, or you can also include more “booster” spices and herbs.

Salts recommended for fermentation are unrefined mineral salts of the earth (Himalayan rock salt from ancient seabeds) and salts of the sea (Celtic sea salt from evaporated sea water). These salts add trace minerals – iron, magnesium, calcium, potassium, manganese, zinc, and iodine – and a deeper flavor to the ferment. As a rule of practice, always avoid refined iodized table salt. Not only is it removed of minerals, the unnaturally high level of iodine and anticaking agents will inhibit the bacteria we are seeking to encourage.

Always measure salt weight by the gram, rather than by tablespoons, to achieve the right concentration of brine and consistency between ferments. The advantage of using Himalayan rock salt is that it is very dry, hence its weight is not affected greatly by moisture. In comparison, sea salt tends to hold moisture (on avaerage 16%), which greatly affects the weight of the salt. However, if you are fermenting a relatively small amount of vegetables, the difference between salts is negligible.

The produce may be salted directly, pre-soaked in brine, or fermented in brine. Either of the methods will suffice, but my preference is to salt the produce directly, cramming it to release it juices, and topping up with brine if necessary. What concentration should the brine be? The optimum salt concentration depends on the type of vegetable or fruit. Generally a salt concentration of 2.5% favors the growth of lactic acid bacteria over spoilage bacteria. However, too much salt (above 3.5%) is detrimental to their growth and eventually kills them, while too little salt (less than 2%) may cause a failed ferment due to the activity of pectinolytic enzymes, mold and yeasts. For direct salting, I scatter 2 teaspoons salt to 4 cups of produce. To calculate the amount of salt to constitute a brine solution, multiply the volume of water in millilitres by the strength of the desired brine. For example, to get a litre of 2 percent brine, multiply 1000 by 0.02 and you will get 20. Add 20g salt to water and dissolve. You could use the handy brine chart below for quick reference.

Salt weight (grams) for desired brine concentration
 250 ml500 ml750 ml1000 ml
1.0 %2.5 g5 g7.5 g10 g
1.5 %3.8 g7.5 g11.3 g15 g
2.0 %5 g10 g15 g20 g
2.5 %6.3 g12.5 g18.8 g25 g
3.0 %7.5 g15 g22.5 g30 g
3.5 %8.8 g17.5 g26 g35 g
4.0 %10 g20 g30 g40 g

Starter Cultures (optional)
Vegetable ferments, including sauerkraut and kimchi, may rely on wild fermentation without a starter culture. Lactic acid bacteria are present in the soil, and therefore on the things that grow in the earth. It appears that the bacteria naturally present in the produce is sufficient to jumpstart lactofermentation.

On the other hand, a starter culture is needed for making dairy-free yogurt and nut or seed cheeses. Dairy-free and vegan-friendly starter culture options include probiotic capsules, finished water kefir, plain kombucha, sauerkraut or kimchi brine, rejuvelac or the ‘whey’ of store-bought dairy free yogurt (this tends to be weak, however).

Sometimes special specific cultures are required, such as symbiotic colony of bacteria and yeast (SCOBY) for brewing kombucha, and water kefir grains for brewing water kefir. These are not strictly lactoferments, but mixed ferments of yeast and bacteria.

Water used for washing produce and to make the brine should be as pure as possible. Tap water is chlorinated to kill microorganisms, including the desirable ones that facilitate fermentation. Fortunately, chlorine has a low boiling point (-34°C) and is unstable in water, so it can be easily removed from tap water by boiling or extended aerating at room temperature for 24 hours. Note that boiling does not remove heavy minerals with high boiling points, so the quality of the resulting water will still largely depend on the quality of your local water supply.

If desired, you can also choose to use filtered water or purified water (the ‘purest’ water possible without minerals or ions), although these will be a more expensive choice.

Spices and Herbs: Booster Ingredients With Antiseptic Properties
Spices and herbs added to ferments not only fine-tune the flavor of the end product but also contribute to inhibit the growth of spoilage bacteria. Aromatic and sulfur compounds in spices (including terpenes and polyphenols) often have anti-microbial and anti-fungal effect, guarding against undesirable microflora while selectively promoting lactic bacteria. Top of the list of antiseptic spices are garlic, mustard seed, cloves and chilies.

Equipment and Tools for Home Fermentation

Here is a brief rundown of the materials useful for preparing fermented foods at home.

Vegetable Chopper
Depending on the cuts desired, this may take the form of a good chef’s knife, mandoline or food processor with fitted blades. The latter tends to produce less even slices and so should be avoided when a consistent cut is desired, for example, in nabak kimchi.

Basin and Vegetable Pounder
A large non-metallic basin is used to hold vegetables for soaking and pounding. Metal bowls and utensils are not recommended as they may transmit small electrical charges that harm the probiotic organisms. A vegetable pounder or stomper is a heavy weight useful for mashing vegetables.

High-powered Blender
For making yogurt and cheeses, a blender is necessary to make a paste of young coconut meat, nuts and seeds.

Fermenting Vessel
Traditional ferment vessels are stone or earthenware crocks. However, it is common and more convenient to use glass jars with air-locks for home fermentation on a smaller scale. Air-locks allow carbon dioxide to escape during fermentation while protecting the food from airborne contamination of mold and dust. These are available for purchase from speciality stores or online. Ensure all fermentation wares are throughly washed and sterilized by soap and high heat before using.

Basic Steps to Lactic Acid Fermentation of Vegetables and Fruits

A basic outline of how I prepare my fruit and vegetable ferments is given below.

  1. Wash raw produce in dechlorinated water. Do not sterilze them with vegetable spray as that will destroy the natural bacteria necessary for fermentation.
  2. Chop to size for the ferment – shred, dice, or leave the produce as large cuts. For example, baechu kimchi uses halved cabbage heads. Smaller cuts will have a more rapid fermentation due to increased surface area. Add other herbs and spices.
  3. For direct salting: scatter salt in produce. Using a vegetable pounder, pound vegetables until the juices are released.

    For pre-soaking in brine: prepare brine solution of desired concentration and soak produce in brine for a period of time until softened. For kimchi, this will take about 6-8 hours or overnight. Drain well.

  4. Press the ingredients down tightly in air-lock fermenting vessel, until their juices rise to the top and covers the produce. Top up with brine if necessary, leaving at least 2 inches from the top. Place the fermenting vessels in warm area. Allow fermentation to proceed for a period of time.
  5. Taste ferment after 2 days and daily thereafter. When it starts to taste tart or tangy, you can move it to the refrigerator. The time at room temperature may range from 3-21 days depending on several factors: whether a starter culture is used, the amount of salt, and temperature.
  6. Storage. Most people find storing fermented vegetables in refrigerator 4-6 weeks improves the flavor. In cold storage, fermentation continues to culture at a very slow rate. A ferment with 1% to 2% salt should keep well for at least 4-6 months in a refrigerator.

Troubleshooting Failed Ferments

This is a list compiled from personal fermentation experiments as well as by other resources found on the web. I hope there is a solution that solves your problem!

Kahm Yeast
Yeast is recognized as a white film with a textured surface resembling spaghetti strands. It may develop if the fermentation solution is insufficiently acidic, insufficiently salted, too warm culture conditions, overexposure to oxygen, or poor hygiene.

Remedy. It is not harmful but if not removed regularly, the yeast will eventually use up the acid, and the food will spoil. It may also impart a bad odour. To minimize the occurrence, use an air-lock system to keep out atmospheric oxygen and always ensure vegetables are under a brine of sufficient concentration.

True Molds
Molds can be distinguished from yeast as they usually appear colorful and round with a fuzzy or fluffy texture. Factors that promote mold development are similar to those that promote yeast development.

Remedy. Moldy vegetables are unsafe and should be discarded. Dispose the moldy vegetables on the surface. Use an air-lock system to keep out atmospheric oxygen and always ensure vegetables are under a brine of sufficient concentration.

Cloudy Brine
Not to worry, some cloudiness is normal and even desirable as it affirms the fecund growth of lactic acid bacteria in the ferment. Usually cloudy ferments are harmless.

Foamy Brine
Not to worry, foam or bubbles reflects the creation of carbon dioxide gas. It is more common when in ferments of higher sugar content, such as beets or carrots. Foaming is harmless and generally disappears after a few days.

Slimy Brine
Slime is likely due to the presence of slime-producing microorganisms. Factors that promote slime development are similar to those that promote yeast development: too weak brine, too warm culturing conditions and insufficiently submerged vegetables.

Remedy. Discard slimy vegetables. To minimize the occurrence, use an air-lock system to keep out atmospheric oxygen and always ensure vegetables are under a brine of sufficient concentration.

Pungent Odour
A strong smelling ferment may be natural, or it could be a truly putrid ferment. If it has mold, try removing the top layer and see if the entire batch has the same odor. Truly putrid ferments could be a result insufficient salt, unclean equipment or using vegetables past their prime. It is safest to discard wholly nasty-smelling ferments.

Ferment Floats to Top of Brine
Place a sufficiently heavy weight on top of the ferment to press it down under brine. This may be as affordable using a brine-filled food-grade plastic bag or glass jar, or specialized ceramic or stone weights.

Ferment Bubbles Out Of Jar
Never fill the fermentation vessel more than 80 percent full. For high-sugar fruit ferments, avoid filling it more than half full. Use an air lock system, check ferment daily and release pressure if necessary. When releasing or “burping” gas, try not to release too quickly as the contents will spurt out and you will have a mess to clean up.

Finished Product Too Salty
You may rinse off excess salt, but this will remove the healthful probiotics as well. Try adding them to bland dishes, or dilute ferment with additional water.

Finished Product Too Soft and Mushy
Soft ferments may be due to spoilage. Check for mold; if there is no mold, the ferment may be salvaged in soups or other dishes where texture is not important.

Vegetables Not Fermenting
The temperature is likely too cool. Fermentation needs a moderately warm temperature (around 70°F or 21°C). If it is much cooler than this, fermentation will be greatly slowed, but not necessarily stopped. If the temperature in your house is on the cool side, consider moving the vegetables to a warm location like next to the refrigerator.

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