How to preserve mushrooms

In this brief guide, we are going to answer the question “how to preserve mushrooms” and discuss the different methods of preserving mushrooms. 

How to preserve mushrooms

The current global market value of fresh mushrooms reached 38 billion US dollars in 2018, and China is the largest mushroom producer within the Asian region, contributing approximately 35 % to the global mushroom market. Asia countries contribute up to 76 % of mushroom production, followed by Europe (17.2 %) and United States (5.9 %) (1).

Mushrooms can be preserved by: 

  • Refrigerating: Fresh mushrooms can be preserved by refrigerating.
  • Freezing: Both fresh and cooked mushrooms can be frozen.
  • Pickling: Mushrooms can be pickled in a brine solution.
  • Dehydrating: Fresh mushrooms can be dehydrated in a food dehydrator.

Mushrooms are best eaten fresh, however, in certain situations they must be preserved.

Refrigerating fresh mushrooms

The storage conditions are highly important for the quality of fresh mushrooms. The best results are obtained by storing in a cool chamber at 0-2°C with relative air humidity of 90%. A study showed that, at this temperature, Agaricus bisporus can be stored for 7-9 days, at 15°C for 2-3 days and at room temperature for 18 hours only (2).

Fresh mushrooms can be refrigerated as follows:

  • Clean the mushrooms by brushing off dirt with a brush or a soft cloth. Do not wash the mushrooms as this will make them mushy and the added moisture may cause spoilage.
  • Place the mushrooms in a paper bag. The paper bag will absorb excess moisture.
  • Fold over the top of the bag.
  • Keep the bag in the main compartment of the refrigerator.

Freezing fresh mushrooms

Fresh mushrooms can be frozen as follows:

  • Clean the mushrooms by brushing off dirt with a brush or a soft cloth. Do not wash the mushrooms as this will make them mushy and the added moisture may cause spoilage.
  • Trim the stems of the mushrooms.
  • If the mushrooms are of a large variety, they can be cut into halves or quarters before freezing. Smaller varieties can be frozen whole.
  • Place them in a zip-lock bag and push out the air. Excess air in the bag will make them mushy.
  • Seal, label and freeze the bag.

Frozen mushrooms can be either thawed or added directly to dishes. They can be thawed by leaving them in a refrigerator overnight. Thawing will make the mushrooms soggy so it is best cooked straight from frozen.

Freezing mushrooms raw is said to decrease their nutritional content, so it is preferable to freeze cooked mushrooms.

Studies show that blanching of mushrooms prior freezing is important and prevents darkening of the mushrooms during storage and defrosting. Blanching should not exceed 1 minute since prolonging bleaching to approximately 5 min results in a distinct hardening. Blanching in water, blanching or soaking and blanching in a aqueous solution of citric and ascorbic acids or lactic and ascorbic acids prior to freezing reduce unfavorable changes in texture resulting from freezing and 12-month frozen storage (3).

Freezing cooked mushrooms

Mushrooms can be frozen after they are sauteed, fried or blanched.

Freezing steam blanched mushrooms: Mushrooms can be blanched in steam before being frozen. This will increase the shelf-life. Blanching may also reduce the loss of nutrients during freezing. Before blanching, mushrooms can be immersed in water and lemon juice to reduce discolouration (1). 

Freezing sauteed mushrooms: Mushrooms can be sauteed in oil or butter and then frozen. Sauteing uses a low amount of fat and high heat so it is believed to preserve the nutrient content in food.

Freezing fried mushrooms: Mushrooms can be deep-fried in oil or butter and then frozen. Deep-fried mushrooms will have a higher content of fat.

Pickling mushrooms

Mushrooms for pickling are either blanched or fried in oil till brown depending upon taste; various condiments as per local preferences and practices are also ground or fried in oil separately and added to the mushroom. The contents are mixed thoroughly and cooked slightly for a few minutes. It is allowed to cool and then filled in the jars. Vinegar may be added for taste and longer storage and the contents in the bottle or the container should be topped up with oil (4).

To preserve mushrooms by pickling :

  • Clean the mushrooms by washing them in running water.
  • Slice the mushrooms if needed.
  • Place the herbs needed for pickling in a mason jar.
  • Make a brine solution by heating water, vinegar and spices. A recipe for pickling with the ingredient quantities can be found here.
  • Add the mushrooms to the brine solution and bring it to a boil.
  • Simmer for 15 minutes.
  • Pour the mixture into a clean pickling jar.
  • Allow the mushroom pickles to cool down.
  • Once cooled, seal the jar and place it in a refrigerator.

Dehydrating mushrooms

Mushroom drying is a standard postharvest technique to ensure long-term supply by reducing water activity to microbial safety levels. It also minimizes many moisture-mediated reactions and effectively inhibits enzymatic and nonenzymatic browning. In addition, drying also increases the variety of mushrooms for consumers. Dried mushrooms have unique texture, flavor and nutritional value and are used in a variety of food formulations (5).

Dehydration is the best way to preserve the flavor of mushrooms. Mushrooms must be dehydrated using a food dehydrator at 110°F (43°C). To preserve mushrooms by dehydration:

  • Preheat the dehydrator to 110°F (43°C).
  • Clean, wash and cut the mushroom into even slices. The thickness of one slice should be about ¼ to ½ an inch.
  • Place the sliced mushrooms on the trays of the dehydrator with spaces in between the slices for airflow.
  • Time for dehydration can vary from 3 to 7 hours. The mushrooms are ready when the slices are crispy and brittle. Check the mushrooms every hour after the 3-hour mark.
  • Once dehydrated, place the mushrooms in an airtight container.

Dehydrated mushrooms can be rehydrated before being used in a dish. To rehydrate, simply soak in boiling water for 20 minutes.

Thermal drying in the presence of UV has been proven to convert ergosterol into vitamin D and enhance the nutritional content of all types of edible mushrooms. Solar drying, hot air drying, freeze drying, microwave drying and infrared drying can be used for mushroom drying under selected operating conditions (5).

Shelf-life of preserved mushrooms

Different methods of preservation result in different shelf-life. The preservation method with the longest shelf-life is dehydration.

  • Refrigerated: Fresh refrigerated mushrooms have a shelf-life of about 1 week.
  • Frozen: Frozen raw mushrooms have a shelf-life of about 12 months (3). Frozen sauteed mushrooms have a shelf-life of 3 months.
  • Pickling: Shelf-life depends on the pickling technique. Quick pickled, refrigerated pickles have a shelf-life of about 6 months (4).1 month.
  • Dehydrating: Dehydrated mushrooms have a shelf-life of 6 months to 1 year.

How to identify spoilt mushrooms

The presence of high bacterial populations in fresh mushrooms is a major factor that significantly diminishes quality by causing a brown, blotchy appearance. There are several indicators that determine the quality of mushrooms, such as whiteness, cap development, stipe elongation, and number of ripe spores, reduction in whiteness or development of browning, weight loss and microbial deterioration (6).

  • Smell: Fresh mushrooms have an earthy smell. Rotten mushrooms have a pungent smell.
  • Texture: Fresh mushrooms are firm while rotten mushrooms feel mushy and slimy to touch
  • Color: Spoilt mushrooms may develop uncharacteristic dark, mushy spots.

Other FAQs about Mushrooms that you may be interested in.

Can you eat mushrooms raw?

Can you eat mushroom gills?

Can you eat moldy mushrooms?

Conclusion 

In this brief guide, we answered the question “how to freeze mushrooms” and discussed the main methods of preserving mushrooms. We also discussed the shelf-life of preserved mushrooms and the methods to identify if mushrooms have gone bad.

References

  1. Mahari, Wan Adibah Wan, et al. A review on valorization of oyster mushroom and waste generated in the mushroom cultivation industry. J hazard mater, 2020, 400, 123156.
  2. Bernaś, Emilia, Grażyna Jaworska, and Waldemar Kmiecik. Storage and processing of edible mushrooms. Acta Scient Polon Tehcnol Alim, 2006, 5, 5-23.
  3. Jaworska, Grażyna, and Emilia Bernaś. Effects of pre-treatment, freezing and frozen storage on the texture of Boletus edulis (Bull: Fr.) mushrooms. Int J refr, 2010, 33, 877-885.  
  4. Rai, R. D., and T. Arumuganathan. Post harvest technology of mushrooms. Chambaghat, India: National Research Centre for Mushroom, Indian Council of Agricultural Research, 2008.
  5. Jiang, Qiyong, Min Zhang, and Arun S. Mujumdar. UV induced conversion during drying of ergosterol to vitamin D in various mushrooms: Effect of different drying conditions. Trend Food Sci Technol, 2020, 105, 200-210.
  6. Singh, Preeti, et al. Recent advances in extending the shelf life of fresh Agaricus mushrooms: a review. J Sci Food Agric, 2010, 90, 1393-1402.