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I know it seems contrary to the current food safety regulations to leave perfectly good food out of the fridge to allow bacteria found naturally in the air to decompose it. When I first started getting interested in fermentation I had to really begin to understand how such practices can be safe and why the current food safety regulations were adopted.
Strictly controlled environment and preservation techniques used to make fermented food prevents the growth of pathogenic and spoilage bacteria, making them safe. Use of salt, pH alteration and controlled access to oxygen ensures unwanted microorganisms are eliminated or minimized.
This is still a foregn concept for many health authorities which think that the elimination of all microorganisms in our environment is the way to healthy food, despite the research indicating that to have healthy food, we need the presence of microorganisms.
There are three main microorganism families which are responsible for producing the fermented foods we now consume on a daily basis. Yeast, lactic acid bacteria (LAB) and acetic acid bacteria (AAB). Each of these families have numerous species within the family which have different properties making them useful or detrimental to specific fermentations.
Environmental Conditions For Safe Fermented Food
| Microorganism | Temperature range | Respiration | Natural fermentation | Inoculation | Salt content | Cleanliness | Ethanol tolerance |
| Yeast | 20-22 °C. or 7-13 °C. | aerobic and anaerobic | yes | yes | no | yes | 4-20% ABV |
| Acetic acid bacteria | 20 to 37 °C | aerobic | yes | yes | no | yes | Up to 12% ABV |
| Lactic acid bacteria | 18 to 22ºC or 20 to 46ºC | anaerobic | yes | Not usually | yes | yes | Up to 10% ABV |
How Yeast Cultures Improve Food Safety
Yeasts have several protective mechanisms which help them to survive. These methods include competition for food sources, high tolerance to ethanol, production of organic acids and production of mycocins (toxins which destroy other microorganisms).
Competition for food sources
Yeast species multiply at a rapid rate when they are placed in a warm environment with plenty of simple sugars. It is this rapid growth rate which crowds out competitors which may be found in a substrate and therefore reducing the populations of other microorganisms.
All organisms need minerals and yeast and bacteria are no exception. One of the studied minerals which is necessary for many pathogenic bacterial growth is iron. Yeast is particularly good at absorbing iron from a substrate making it unavailable to these pathogenic bacteria.
High Ethanol Tolerance
One of the byproducts of yeast respiration is various types of alcohol, the main one being ethanol. Several yeast species which are prevalent in fermentation are Saccharomyces cerevisiae which have a particularly high tolerance to ethanol.
Ethanol inhibits microbial growth due to its ability to cause leakage of the membrane which surrounds a bacterial cell. As the cell loses its ability to control its environment its growth rate decreases.
When yeasts are competing in nature without human intervention they naturally fill a niche which helps to break down organic material. Once their main source of food (simple sugars) has been consumed their population declines and other microorganisms take over such as mold and AAB.
Production of organic acids
Organic acids reduce the pH of a substrate which inhibits the growth of pathogenic and spoilage microorganisms. The WHO recommends a pH below 4.0 to ensure food safety. Although yeast is not known for its production of acidic substrates like LAB or AAB, it still lowers it enough to inhibit the growth of some unwanted microbes.
Production of mycocins
Mycocins produced by yeast species are designed to prevent the growth of other microorganisms in the yeast’s environment. This is one of the ways it protects itself from being overwhelmed by other microbes.
Environmental Conditions Yeast Need To Safely Ferment Food
By controlling the environment which the yeast species are present in they can effectively preserve a food product past its effective shelf life. There are basically three environmental conditions which are needed when using yeast to preserve food.
- Anaerobic fermentation
Anaerobic fermentation is done by placing the food into a container which controls the access to oxygen. By placing an air trap on the opening of the container which allows the one way travel of air from inside the container to the atmosphere. This prevents oxygen from entering into the fermentation.
Molds are aerobic organisms (they need oxygen) so by preventing oxygen from entering into the fermentation they cannot grow so just this method reduces the risk of growth of pathogenic and spoilage bacteria. Another side benefit of anaerobic fermentation is the limited growth of AAB which turns the alcohol into vinegar, which is undesirable for alcoholic fermentations.
- Temperature control
All life has a temperature range which it grows the best. Beneficial yeast have a range of 20-22 °C. or 7-13 °C. If the fermentation is kept within these bounds other microbes who’s ideal temperature range is outside of the fermentation temperature find it difficult to multiply.
- Cleanliness
Starting with a clean environment will give the desired culture a boost. Yeast will be able to overwhelm most other microbes in a substrate with adequate food when placed in an anaerobic environment and kept at its optimal temperature but if it has to compete with a large population of other microbes the resulting fermentation may still be not suitable for consumption.
Molds are prevalent in the environment and can grow on a variety of surfaces just as long as they have enough water and heat. They break down starches into short chain sugars which disintegrates the structure of the surface they are growing on. As they do this they produce harmful mycotoxins which can cause sickness or even death. By starting with a clean environment the risk of this is mitigated.
How Lactic Acid Bacteria Improve Food Safety
Lactic acid bacteria are responsible for the tangy flavor found in sauerkraut, fermented pickles or other vegetables. They are the most prevalent bacteria found in yogurt and kefir lowering the pH of the milk which causes it to thicken. They also have bio-protective effects which provides this type of fermented food from spoilage.
- Anaerobic fermentation
Unlike yeast, LAB are strictly anaerobic bacteria and can survive in a sealed container. This gives them a distinct advantage when placed into a sealed container without access to oxygen.
To accomplish this there are two methods fermentors use:
- Use a sealable container with one way air travel like a water sealed crock or an air locked container.
- Ensure all food is submerged below the liquid during fermentation
- Addition of salt
LAB are very salt tolerant. They can survive in salt concentrations up to 10% salt by weight in water. Other microbes are not as adapted to this including yeast, mold and AAB. By using a high salt concentration when making lacto fermented vegetables you are inhibiting the growth of these other microorganisms and allowing the LAB free reign.
- Use of inoculation
Some fermented foods do not benefit from the addition of salt, products like yogurt, kefir and cheeses of various types. For these type of products the fermentation is inoculated with an active culture which can quickly adapt to its environment and dominate the substrate.
When inoculating a fermentation the purpose is to give a chosen culture a head start from all the other microorganisms in the environment. Once they outnumber the other microbes it leaves little room for others to grow.
- Temperature control
Depending on the method and the food you are fermenting changes the fermentation temperature.
- Vegetable fermentations are best when fermented at 65°F (18°C) but can tolerate 72°F (22°C).
- Milk fermentations are performed in the range of 68°F (20°C) to 115°F (46°C) depending on the product you are making
How Acetic Acid Bacteria Improve Food Safety
AAB are the bacteria which produce vinegar which is not only used directly on and in food but are also used to preserve food products for long term storage.
There are two types of pickles, lacto fermented pickles which we talked about in the previous section and acidified pickles which are made using canning techniques and vinegar.
- Aerobic fermentation
AAB are aerobic bacteria, they need oxygen to reproduce so when using AAB the container used has a wide mouth to allow for oxygen exchange. The mouth of the container is covered with something which is porous to keep dust and debris out of the fermentation while still allowing oxygen in and carbon dioxide out.
- Presence of alcohol
AAB’s energy source comes mainly from ethanol. Ethanol is consumed and converted into acetic acid (vinegar). This is why the wine and beer industries go to great lengths to prevent oxygen and AAB into their batches.
The presence of ethanol in the liquid provides adequate food resources for the AAB but limits the growth of mold and spoilage yeast. Most yeast species are not highly tolerant of alcohol and die off once the ABV reaches 4%, whereas AAB grow well in a soulution which contains up to 10% ABV.
- Acidic starting solution
AAB are also highly acid tolerant. They can live in solutions with a pH of 2.5 where most unwanted microorganisms cannot survive once the pH gets below 4.0. By lowering the pH of the solution you are fermenting with AAB you effectively prevent the growth these unwanted microbes.
- Temperature control
AAB have a specific temperature range which they grow well in. By controlling the temperature within this range they have the best chance of dominating the culture while others outside of that range are inhibited. The Temperature range for AAB is between 68°F (20°C) to 98°F (37°C).
Are fermented foods safer than fresh
Okay so fermented foods are safe but they are also safer than fresh. How can a piece of fruit or a chopped up vegetable left to decompose in a jar with some salt and water be safer than the fresh version?
The action of the fermenting microorganisms destroys pathogenic bacteria making them safer than their fresh versions. Pathogens like Listeria monocytogenes, Salmonella and E. coli have been found on fresh lettuce in the past year. Not only does fermentation of fresh vegetables destroy pathogens but it also breaks down the harmful toxins which are produced by these unhealthy microbes.
Fermentation also helps to break down pesticides and other toxic chemicals which are used on most industrial food. It is common knowledge the damage which can be caused by consuming pesticide laden factory produced food whether it be fruit and vegetables or meat and since the industrial food model hides how their food is produced fermentation is a great option to reduce the exposure to these harmful chemicals.
Can fermented food be eaten every day
Most likely you are already eating fermented food every day. You probably eat bread and cheese, drink coffee or eat chocolate, put vinegar on your salad and eat yogurt or kefir in the morning.
Fermented foods are generally regarded as safe according to the FDA and can be consumed on a daily basis. Some individuals may experience uncomfortable side effects from eating a new fermented food therefore it is best to introduce new foods slowly into the diet to determine its effects.
It is important to know that eating live fermented food can have drastic and uncomfortable repercussions. Live fermented foods like sauerkraut, kefir and kimchi can cause bloating and discomfort at first while your system gets used to them. Start with small amounts of them and increase your consumption slowly to avoid being uncomfortable.
If you are sensitive to a particular food then avoid fermented foods made with that ingredient. Fermentation does not eliminate allergens from food although they do add
Who should not eat fermented food
Nobody! Fermented foods are prevalent in every culture and part of the world.
Some people may not be able to eat specific types of fermented foods but to eliminate all fermented foods from a diet would unrealistically restrict the food choices available. Individuals who are sensitive to specific food types such as milk or cabbage should avoid fermentation which uses these as their base but depending on why the individual is sensitive, fermentation can improve the tolerance for such foods.