Learn how to Ferment Mushrooms & why you should | OGM! (2025)

Benefits of fermented mushrooms

Firstly, it’s very easy to ferment mushrooms. In addition, the process increases many of the inherent nutritional and health benefits of the mushrooms.

• It causes a significant increase in protein content.
• A decrease in carbohydrates and fat.
• It will increase the quantity of several important minerals including calcium, magnesium, potassium, manganese, iron, and sodium (to reduce sodium use calcium chloride CaCl instead of plain cooking salt (aka sodium chloride or NaCl).
• Maintains many of the health attributes found in raw mushrooms
• Releases several beneficial components found in the mushroom that would not otherwise be digested.
• It’s a superior source of both pre and probiotic material for your body.

How does fermentation work?

If you are new to fermentation, here’s a quick summary of how it works.

• Lacto fermentation relies on the fast growth of Lactobacillus bacteria which will create acids (like vinegar) decreasing the pH.
• These lactic acid bacteria are often referred to as LAB. The increase of acidity kills harmful bacteria and is what gives the ferment its zesty & sour taste plus a long shelf life.
• The fermentation process takes place in an air-free (anaerobic) environment, which is usually achieved by performing it underwater. This water comes from the liquid drawn out of the mushroom (or plant) by salting it.
• The saline solution also inhibits the growth of other undesired organisms (like moulds, yeasts and some harmful bacteria).

What are Lactobacillus bacteria?

Lactobacillus bacteria is considered a beneficial, or healthy bacteria, which is also an essential part of our bodies. It is also used to make yoghurt and cheese. They are present in our gut, where they also naturally ferment food to release nutrients that our body would otherwise not be able to digest. They also form the basis of healthy gut flora.

Why is fermented food good for our bodies?

Eating fermented food provides 2 healthy outcomes. 1) it is a way for us to populate our bodies with important bacteria (pro-biotic) to maintain a healthy body. 2) It also introduces a food that can not be digested in the upper parts of the digestive tract, so acts as food for the healthy bacteria already living deeper in our gut.

On a side note, one of the outputs of fermentation is gas (generally CO2) so you’ll know how well your body is fermenting things by the amount of gas you produce.

The following information is written primarily for people familiar with the fermentation technique. However, for newcomers, it also does a good job of explaining the fundamentals of fermentation. Don’t be put off if the fermentation seems difficult because it isn’t. It is a very simple and natural process. Several recipes at the bottom of this article will step you through the process.

Are mushrooms safe to ferment?

Mushroom fermentation has a long history. It is the preferred method of several traditional cultures (eastern Europe and Asia) as a way of preserving and storing mushrooms. More recently, mushroom fermentation has been rigorously tested through lab research to ensure food safety. This testing has mushrooms categorised as very safe for fermentation.

What preparation is required?

Like all ferments, only the best and freshest mushrooms should be used. Cleaning is an important process especially if mushrooms are foraged. Wash in cold running water and remove any damaged or rotting portions. Take care not to damage the fruit. For mushrooms with thick woody stems, only the caps are used. For mushrooms like Oysters or smaller mushrooms, you can use the whole thing. If the cap is thick, it should be sliced.

Do I need to blanch first?

The main purpose of blanching is to remove excess air and reduce volume, so more can be packed into the container. Mushrooms have enzymes and other undesirable bacteria that can lead to a fresh mushroom “going off” very quickly. So, unless you have a starter culture to deal with this, it would be best to blanch the mushrooms first.

• The recommendation is 3-4 minutes in boiling water.

Note: Care should be taken as blanching can destroy many of the mushroom’s unique health properties. In lab tests, it was found that the total phenol content decreased by 60% and the antioxidant capacity decreased by 54%.

Should I add salt?

Salt is used in the fermentation process to draw out liquid from the mushroom (thereby submerging it in water). More importantly, the saline environment inhibits many other bacteria and organisms that will spoil the ferment without affecting the LAB.

People experienced in fermentation will often rub the salt in by hand, rather than mixing it with water first. The contact with the hands helps introduce lactobacillus bacteria.

Note: Table salt (with iodine) should be avoided. Salts not containing iodine are often labelled as kosher or pickling salt. Here’s a link to info regarding fermenting and salt

• 2% salt is recommended

Do I need to add sugar?

The mushroom’s carbohydrate profile, including complex sugars like polysaccharides, allows it to be fermented without the addition of sugar.

• If sugar is used 1% is recommended.

Adding sugar is recommended if not using a starter culture.

Is acidifying (adding vinegar) required?

If you follow the guidelines in preparing the ferment, you generally do not need to add additional acids like vinegar. Adding vinegar is often used in pickling mushrooms (a similar food preservation technique) where fermentation is not the goal and you wish to still make it shelf stable. Note achieving an acidic pH level of less than 4.5 (either through fermentation or pickling) is essential in making and keeping the food safe.

If you are unsure about your fermentation skills, adding vinegar will push pH down to a level where you can make the food safe in the initial days. Until the ‘LAB’ population increases sufficiently it can finish the job.

If using vinegar we recommend raw cider vinegar like Bragg Certified Organic Raw Apple Cider Vinegar. A raw vinegar will add bacteria that may increase the acetic acid profile.

Do I need a starter culture?

Due to the mushroom’s high moisture content and neutral pH, a starter culture (or back slopping) is recommended. These “back-slops” can be sourced from an earlier, successful ferment. The “juice” from a sauerkraut ferment has been found to work well.

However, mushrooms can be successfully fermented without the need to add a culture. In this case, it may be prudent to add some vinegar to increase acidification in the early stage, and also add some sugar to get the LAB producing sooner.

Note: Lactobacillus Plantarum (a type of LAB culture used for fermentation of plant material) is mainly used for the fermentation of mushrooms. It has also been found that the use of the L. Plantarum 299v probiotic strain enhanced an increase in the antioxidant activity and other phenolic compounds of fermented mushrooms to a level similar to that of fresh mushrooms.

We have successfully used cultures that are used for making yoghurts. Best are cultures used for plant-based yoghurts. These strains of LAB will be more suitable for the mushrooms.

How long do I need to ferment mushrooms?

Fermentation is usually carried out at a temperature of 18 to 26 °C for a period of several to 30 days. Mushrooms fermented at a lower temperature (around 20 °C) have been reported to have better quality.

If the final product requires longer storage, the safest length of time would be a ferment of +18 days. This ensures that the pH level has decreased (aim for a pH less than 4) to the point that all undesirable bacteria and yeast should have been eliminated. A 30-day ferment should have a pH of around 3.5.

Note: Populations of undesirable bacteria may increase in the first few days of the ferment, so for shorter ferments, it would be appropriate to add vinegar.

Once fermented, how long will they keep?

Generally, this will depend on how cool it is kept. It should be good for at least 4 weeks but if stored properly, it should remain stable for up to 6+ months. The cooler the better, as it will slow the fermentation down to a level where the texture and taste of the mushrooms are maintained. Adding a small amount of oil may also help durability for longer storage, but may pose a rancidity problem if it is exposed to air. The high CO2 environment of an unopened jar should stop this.

Pasteurisation is not required but it may help to improve the quality of longer stored products. Pasteurisation will not affect the antioxidant capacity and the content of phenolic compounds, however, it will destroy the probiotic capacity by killing the live lactose bacteria.

A pH of 3.5 or less means it will be shelf-stable. Once sealed it should keep for 6+ months without the need for refrigeration. For pH above 3.5 refrigeration is required to stop the growth of undesirable microbes.

What should I ferment the mushrooms in?

Bag method: This is our preferred method. This is done in a food-safe plastic bag which makes it easy to squeeze out all the air and seal it. Make sure the volume of the bag is at least twice as large as the volume of the ingredients. This allows plenty of head space should the pressure increase and not blow the bag. Once the main fermentation is done, transfer it into jars for storage.

For us, the bag method offers several advantages.

• It’s easier to create the anaerobic conditions required.
• it allows us to do large batches of about 5kg (10lb) at a time,
• Perhaps most importantly, you can quickly determine if the fermentation is working by visually seeing if the bag swells up with CO2.

Fermenting in Jars: Jars are great for smaller batches but can be a little tricky removing the air. There may also be issues of the gas buildup forcing liquids out and compromising the seal.

Fermentation Crock: These are great. Chances are, if you have one you know how to use it.

NOTE: the mushrooms do not contain as much water as cabbage and other vegetables, so it is unlikely that the salting will produce enough liquid to submerge the ingredients. This means a little extra caution when using a jar or crock in creating an anaerobic environment.

Further research

• From the legendary Noma Restaurant in Denmark, here’s their recipe for Lacto cep mushrooms. See the suggested uses for turning this into a Desert: https://nationalpost.com/life/food/cook-this-lacto-cep-mushrooms-from-the-noma-guide-to-fermentation
• Food Value and Safety Status of Raw (Unfermented) and Fermentedmushrooms: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6195889/
• Preservation of King Oyster Mushroom by the use of different fermentation processes: https://ifst.onlinelibrary.wiley.com/doi/abs/10.1111/jfpp.13396

Citation

Much of the information provided here was sourced from

• Scientific (literature review) of academic research in fermenting mushrooms: https://www.sciencedirect.com/science/article/abs/pii/S0023643815303662