Fermentation is a fun and creative hobby that produces new flavors which can add interest to any meal.  I started to make my own ferments by making kombucha after drinking the store bought version for a year or two.  Once I started making kombucha it was easy to branch out to other fermentations.

Today I have a cupboard full of new and strange experiments from normal fermentations like kefir, sauerkraut and kombucha to more difficult and long term fermentations like miso, soya sauce and vinegars of all types. The preservation of food through the use of fermentation is an ancient practice which adds new foods to your diet while taking part in history but before you begin on any new fermentation project here are a few things to do to ensure success.

Start with familiar types of fermentation

If you grew up on a meat and potatoes diet then don’t start your fermentation journey with Natto or miso making.  These fermented foods, although very good, may be too much of a departure from your normal diet that you may not want to continue.  Instead make pickles, sauerkraut or yogurt.

Once you get the hang of making some of the fermented foods you would normally eat you will be much more inclined to like the more funky fermentations like kombucha or tempeh.  These and other fermentations have some characteristics which can be hard to get past (slimy growths growing on the surface and mold spores growing on the beans) but once you start to enjoy the flavors which can be achieved from various fermentations you will begin to look forward to new ones. 

Try the commercial version first

There is nothing worse than spending time and energy learning how to make a new fermentation, waiting the required amount of time to taste it only to find you don’t like it.  Avoid this by trying the commercial version, if it is available, before you try the homemade version.

Fermented food like yogurt, kefir and sauerkraut are good starting foods because of their availability.  Make sure you try the cleanest and freshest versions which are actually fermented.  When buying yogurt or kefir look for plain types with as few ingredients as possible.  Most commercial brands include thickeners, added sugar and other ingredients to maintain quality during transportation and handling. 

If you want to start with sauerkraut try some which has actually been fermented.  There are several brands of sauerkraut which are made with vinegar and canned rather than fermented naturally.  Make sure you try fermented sauerkraut before you make some yourself as it has a different flavor then the canned type.

Some fermentations are not readily available at grocer like tempeh and natto but they can be found at health food stores or asian grocers.  These fermentations are a little more involved to make, so be sure you like them (or you think you can learn to like them). Here are ten reasons why you should learn to like natto.

Decide on ONE type of fermentation and expand from there

There are as many types of fermented foods as there are cultures and subcultures in the world.  Way too many to learn all at once even if you had the space or time to do it all.  Just as fermentation is a slow food your growth in fermentation should also be slow.  You may find you like only a few projects bubbling away in an unused section of the kitchen or you may end up with a fermentation room chalk full of new and interesting things.

Just don’t go crazy and try to ferment everything in sight!  Try one thing, after a few successful batches try another and soon you will have several projects which can keep you busy.  Just keep in mind that they all need attention.  

Learn some history about the fermented food you want to make

History is a great teacher, this is where the saying hindsight is 20-20 comes from.  You can learn a lot about how and why a fermentation was made the way it was from the history of the food.  For example, did you know that sauerkraut, the famous German staple, was not first made in Germany.  Instead it is believed to have come from China and made its way to Germany through trade routes.

Kombucha, one of the most popular homemade ferments also first appeared in China but quickly made its way to Japan where it was refined and used as a healing tonic for thousands of years before it was commercialized and sold worldwide.

Kefir was first made in the caucasus mountains and was a closely guarded secret even among the klans.  It was thought that they would lose their healing power if the grains were given away.  This obviously slowed their spread throughout the world but now kefir can be found in most grocery stores.

The history of a fermented food will also give you an idea of how it can be made.  As an example sauerkraut was traditionally made in the fall when the cabbages were being harvested.  The ambient temperature was cool and got cooler as the season went on.  Nowadays fresh cabbage can be found year round so you can ferment them in the heat of the summer but if you do you will have to either find a cool location or endup with mushy sauerkraut.  

Make short duration ferments

Fermentation is a slow food.  There are no microwave fermentation recipes, they all take time for them to mature.  Vinegar can take up to six months before it is ready to taste, sauerkraut takes at least two weeks but is better after three or four.  Miso, soya sauce, and most alcoholic beverages all take six months to a year before they are tasteable and are better with age.

Unless you are the most patient person in the world you may want to start with a shorter term fermentation like yogurt, kefir or sourdough bread.  These fermentations can be made in 24 hours or less and will provide quicker results.  

Once you have made a few batches of these short term fermentations expand to some which take a little longer such as kombucha, sauerkraut or fermented hot sauce.  These take two to three weeks before they are ready to consume so they are good midrange fermentations to try.  They can be started and left alone for a while giving you time to learn about other longer term fermentations.

Long term fermentations like miso and vinegar are time intensive to make at the beginning but once they are in the aging stage can be left for months.  The challenge with the first few batches is leaving them alone.   They need six months to a year before they are really mature enough to begin using them.

Find a reliable source of information

There are several benefits of making and eating fermented food.  They are flavorful, store for a long time, provide cultural experiences and are also healthy and can provide great sources of vitamins and minerals.

Again it is impossible to be an expert in all these areas of fermentation and you may not be interested in all of them.  You may be only interested in how things taste and what you can create in the kitchen with these new flavors or you may be interested in the health benefits which can be derived from fermented foods.

Find a source you can trust.  When someone suggests making sauerkraut ice cream maybe they are not a good source for tasty recipes.  If someone states you have a high probability of dying from acidosis if you drink kombucha three days in a row or cite old FDA warnings about kombucha to warn you off making it then it is time to find another source.

On the other hand sources which take a flippant attitude to food safety, relying on the bacteria to protect the food from spoiling or harmful bacteria should also be avoided.  Sources which overemphasize the health benefits over their known health effects should also be taken with a grain of salt. Yes, fermented foods, as a whole, are good for you, they provide valuable vitamins and minerals, improve digestion and can help some medical conditions but they are not a cure all.    

How to Start Fermenting Yogurt and Kefir

These are the shortest fermentations around,  they can take less than 6-24 hours to complete and will produce a product which is familiar to the versions you can buy at the store.

There are three ways yogurt and kefir can be made.  You can learn all three by reading “Three Simple Ways to Make Yogurt” and “Three Ways to Make Kefir an Illustrated Step By Step Guide” but here is the easiest method for both to get you started.

How to make yogurt for the absolute beginner

You will need:

1. One glass jar with a lid
2. A pot with a lid
3. A food thermometer 
4. A whisk 
5. Fresh milk
6. Some store bought yogurt with the least additional ingredients
7. An oven with a light or cooler and hot water bottles

Instructions: 

1. Fill the jar with milk leaving an inch and a half of head room
2. Pour the milk in the jar into the pot and slowly heat to 180℉ or 82℃
3. Maintain temperature for 20-30 minutes
4. Pour the milk back into the jar
5. Wait until milk is below 115℉ or 46℃
6. Stir in enough store bought yogurt until it comes to ½ an inch from the top
7. Place the lid on the jar and put into the oven with the light on or into the cooler with the hot water bottles
8. Wait 6-12 hours until it has thickened
9. Refrigerate the yogurt for at least two hours before trying it.

How to make kefir for total beginners

Kefir is absolutely the easiest fermentation there is.  There is no heating of the milk, incubating at specific temperatures and a wide variety of milk or milk substitutes can be used.

You will need:

1. A glass jar with a lid
2. An elastic band
3. One piece of cotton cloth
4. A whisk
5. Store bought kefir
6. Any milk of your choice

Instructions:

1. Fill the jar with fresh milk leaving 2 inches of head room

2. Place ¼ cup or so of store bought kefir into the jar

3. Whisk the milk and kefir together
4. Place the cloth over the top of the jar and secur it with the elastic band

5. Place it in an out of the way location for 12-24 hours
6. Once the kefir has thickened replace the cloth with a lid and store in the fridge

How to Start making Lacto Fermented Vegetables

Lacto Fermentations are still very easy to make although they require some calculation to ensure a quality product.  Lacto fermentations use lactic acid bacteria (LAB) which flourish in anaerobic (no oxygen) environments and are very salt tolerant.

Knowing this makes it easy to understand why fermentations like sauerkraut can be made with the assurance that they will be healthy and taste great.  All you need to do is control these two conditions.

The anaerobic environment is easy, put the vegetables in a lidded jar with enough liquid to submerge them. Make sure you relieve any pressure which builds up inside the container by either using an air lock system of some type or burping the jar regularly. .  

The Salt should make up at least 2.5% of the fermentation by weight to ensure mold and unwanted bacteria do not grow.  Salt also helps to keep vegetables crisp and adds flavor.

You can do this in two ways:

1. Use the weight of water which would fill the container
2. Weigh the container after it has all ingredients besides the salt and calculate the required salt.

How to Make SauerKraut For Total Beginners

Sauerkraut is the simplest lacto fermented vegetable fermentation there is.  There are two ingredients in basic sauerkraut, cabbage and salt.  Additional spices can be added like caraway seeds, garlic or dill but they are unnecessary for fermentation to occur.  There are thousands of recipes online for this lacto fermented classic but start by making this simple recipe.  Once you have been successful then try some new flavors.

You will need:

1. A nonreactive container such as a flip top jar, fermentation crock or mason jar
2. A kitchen knife
3. Kitchen scale
4. Cutting board
5. One head of cabbage
6. Salt 

Instructions:

1. Trim the end of the cabbage and remove any outside leaves
2. Weigh the cabbage on a kitchen scale
3. Measure out the salt (weight of cabbage X 0.025 = amount of salt needed)
4. Slice the cabbage into roughly even slices
5. In a large bowl mix the salt and cabbage together and knead until combined
6. Let sit for 15 minutes to allow the salt to begin to drawout the liquid in the cabbage
7. Pack the cabbage into your fermentation container submerging the cabbage below the liquid
8. Seal the container and place it in a cool dark location
9. If using a mason jar or other container which does not release pressure burp the container every day or two
10. After two weeks try some to see how it is coming
11. Move to the fridge once it reaches the level of fermentation you like

Note:

If you are using a mason jar you will have to seal it in some way which allows carbon dioxide to escape to avoid potential explosions and injury. 

How to Make Pickles For Total Beginners

Pickles have their own set of challenges.  They should be crunchy, tangy and brightly colored but cucumbers which contain large amounts of water and very little hard cellulose material which maintains their structure.

There are more recipes on line for crisp pickles than anyone could ever read.  The ingredients include “secret” ways to keep pickles crispy, maintain their color and make the most tangy and delicious pickles ever.

All these recipes have a few things in common:

1. High salt concentrations of Brine

Pickles are traditionally made using a brine solution which is between 3.5-5% salt by weight.  This brine does not take into account the weight of the pickles.  It is only the weight of the water so the higher concentration of salt in the water makes up for the additional water from the pickles which dilutes the brine as the pickles ferment. The higher the salt concentration the more water will be drawn out of the cucumbers during the first stages of fermentation making the pickles crispier.

To easily calculate the amount of salt needed for a batch of pickles simply determine the weight of the water it would take to fill the jar. This is a fairly consistant weight (it does vary a little with temperature and altitude) but for your purposes it will work fine.

Water weighs 8.33lbs per gallon so if your container holds a quart of liquid then divide 8.33 by four to get 2.08lbs. calculate a 2.5% brine to get 0.6656 ounces (after converting lbs to ounces). Since cucumbers are less dense then water you will have ample salt by weight to keep the mold growth under control.

2. Additions of some type of tannin

These include bay, grape, black tea or oak leaves.  Tannins help to keep the cucumbers crunchy by preventing the breakdown of the cell walls in the cucumber.  

3. Cool temperature fermentation

This slows the fermentation process down, giving the salt in the brine time to remove some of the water from the cucumber and preventing unwanted mold and bacterial growth.  

It is mold which can degrade the cellulose in vegetables.  Mold is able to break down the  complex carbohydrates which make up the structure of the vegetable.  By preventing mold growth at the first stages of fermentation the pickles remain firm. 

4. Longer fermentation time with a cool temperature

A cool fermentation temperature prevents mold from growing in the fermentation and allows the salt in the brine to draw out the most amount of water.

Since the cooler temperature slows the growth rate of the LAB the fermentation time needs to increase.  Once they have consumed the bulk of the sugar in the cucumber the fermentation will slow but the pickles will remain firm.  

5. The addition of some sugar

Refined sugar to LAB is like nitrogen fertilizer to plants.  It makes them grow fast.  Giving the LAB a little sugar in the brine increases the potential acid production and reduces the amount of time it takes them to dominate the culture.  This makes for more tangy pickles with less chance of off flavors appearing.

6. Cut the blossom end of the cucumber off

The blossom end of the cucumber is rich in yeast species due to the pollinating insects which visited the flower. By removing this section of the cucumber the yeast population will be lower and less varied leading to crisper pickles.

7. Stab the cucumbers several times or cut them into pieces

This enables the salt in the brine to draw out more of the water in the cucumbers prior to fermentation.  This leads to firmer pickles with less yeasty flavors.

You will need:

1. A jar with a lid
2. A cutting board
3. A knife
4. Kitchen scale
5. Enough cucumbers to fill the jar leaving an inch of headroom
6. Some type of leaves to add some tannin
7. Water
8. Salt 

Instructions:

1. Wash the cucumbers in water
2. Cut the ends off each of the cucumbers
3. Slice the cucumbers in half lengthwise
4. Load the cucumbers into the jar and fill with water leaving an inch of headroom
5. Calculate 2.5-3.0 salt concentration by weight of the water
6. Add the salt and place the lid
7. Add the leaves for tannins
8. Shake the jar until the salt dissolves
9. Open the jar and ensure all cucumbers are under the liquid
10. Place the jar in a cool location out of the sun
11. Burp the jar daily while the fermentation is active
12. After two weeks try your pickles and refrigerate when they reach the flavor and texture you like

How to Make Pickled Carrots For Total Beginners

Carrots are full of sugar which makes them ideal candidates for fermentation.  The LAB will consume the sugar in the carrots and produce ample amounts of lactic acid.  Since carrots are hard root vegetables they hold their crispy texture longer and under less ideal situations.

This makes them great for a beginner fermentation project.

You will need:

1. A knife
2. A cutting board
3. A non-reactive container
4. A kitchen scale
5. Enough Carrots to fill the container with an inch or so of headroom
6. Water
7. Salt

Instructions:

1. Cut the carrots up so they will fill the jar leaving an inch of headroom
2. calculate the amount of salt needed for a 2.5% water solution
3. add enough water to cover the carrots
4. add the salt
5. shake the jar untel the salt is disolved
6. place in a cool dark location
7. if the jar is not pressure safe burp the jar daily to prevent carbon
8. Follow the instructions of how to make pickles above starting at step three

How to Make Kombucha For Absolute Beginners

As I mentioned in the introduction, kombucha was my first fermentation and I still make a large batch of my regular kombucha every two weeks or so.  I am also experimenting with new and different flavors, methods and infusions.

Kombucha is not hard to make once you understand the processes which are taking place and how to work with the culture.  Kombucha is unique in its culture makeup as it contains all three of the main fermentation microbial species: 

1. Yeasts
2. Acetic acid bacteria
3. Lactic acid bacteria

It is an aerobic fermentation which means it needs oxygen and uses the backslopping method to instigate fermentation.

You will need:

1. A one quart sized clean glass jar
2. A clean cloth with an elastic band
3. A bottle of raw plain commercial kombucha
4. |One Tablespoon of tea loose leaf or two or three tea bags of your choice (start with black or green tea)
5. 1/3 cup of sugar
6. Water

Instructions:

1. Make enough tea to fill the jar ¾ full
2. Remove the leaves or bags after 5 minutes
3. Add the sugar 
4. Let cool to room temperature
5. Add the commercial kombucha to fill the jar
6. If you find a SCOBY in the jar add it as well
7. Place the cloth on the top of the jar
8. Wait two weeks for the kombucha to acidify

Once the kombucha has acidified you can drink it plain or make it into kombucha soda.  Be sure to save the SCOBY and some starter liquid for the next batch. 

How to Make Vinegar For Absolute Beginners

Vinegar is actually a double fermentation product.  It requires the fermentation of alcohol from sugar performed mostly by yeasts and then the conversion of the alcohol into acetic acid by acetic acid bacteria.

Sometimes this happens simultaneously and sometimes it is done in two steps.  For this tutorial I will use the second method of starting with some already finished alcohol.

You will need:

1. A wide mouthed jar
2. A cloth with an elastic band
3. A bottle of alcohol with a ABV between 5-12%
4. An appropriate type of vinegar

Instructions:

1. Fill the jar ¾ full with the alcohol
2. Fill the remaining space with the appropriate vinegar
3. Place the cloth over the top of the jar and secure with the elastic band
4. Place in a location out of the sun
5. Wait

This method of vinegar making is slow and can take up to to six months before the vinegar is ready.  In that time a vinegar mother may form on the surface of the liquid.  This cellulose formation protects the vinegar from contamination as well as helps with oxygen exchange.

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. 

1. 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. 

2. 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.  

3. 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.

1. 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

2. 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.   

3. 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. 

4. 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.  

1. 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.

2. 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.

3. 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.

4. 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.