Safe Handling of Mushrooms

Mushrooms are the fleshy part of a fungus and usually grow on composted materials and nutrient sources, such as a tree log. There are many types of edible mushrooms, including white “button” mushrooms, portabella mushrooms and shiitake mushrooms.

Mushrooms can be part of a nutritious diet and provide many nutrients that your body needs. Canada's Food Guide recommends a diet rich in vegetables and fruits to help maintain a healthy life.

How can mushrooms become contaminated?

Fresh mushrooms and other fruits and vegetables don't naturally contain bacteria that can make you sick.

Because farmed mushrooms are usually grown on sterilized composted material, they can become contaminated if the compost is not sterilized properly. Mushrooms can also be contaminated by water, wild and domestic animals or improperly composted manure. Bacteria may also be transferred during and after harvest from handling, storing and transporting.

The conditions in which mushrooms are packaged and stored can also contribute to the growth of bacteria. Because mushrooms are often stored unrefrigerated in airtight packaging, botulism is a particular concern with packaged fresh mushrooms. Without oxygen, mushrooms in this environment allow the bacteria that cause botulism a chance to grow and produce toxins before you can see any signs of spoilage on the mushrooms.

How do I select mushrooms at the grocery store?

You should choose fresh mushrooms with no signs of spoilage and bruising.

With fresh, loose mushrooms, choose the ones that are firm and the same color. Prepackaged, fresh mushrooms should be in plastic wrapping or film that has holes in it to allow air flow through the container to prevent the growth of botulism.

Storing Mushrooms

Mushrooms should be eaten fresh and as soon as possible after you buy them. Loose mushrooms should be kept in a paper bag in the refrigerator. Keep your packaged mushrooms in the refrigerator in their original packaging until you open the container. They can be kept in the refrigerator at 4ºC (40ºF) or less for up to five days in a paper bag or in the original packaging to maintain their quality.

Fresh mushrooms should not be frozen. If you would like to freeze mushrooms, they should be steamed or sautéed in a frying pan first. Cooked mushrooms can be kept in the freezer for eight to twelve months.

Cleaning and Preparing Mushrooms

Mushrooms can be cleaned gently with a damp cloth or a soft bristle mushroom brush. You can also rinse them under fresh, running water and pat dry with paper towel. Pay special attention to the underside of the mushroom, because the flesh under the mushroom cap can easily store bacteria and viruses. For quality reasons, do not wash mushrooms until you are ready to use them.

There is no need to use anything other than water when washing mushrooms. Produce washes may not completely remove or kill bacteria, viruses and parasites. Washing mushrooms gently under fresh, running water is at least as effective as using cleansers. 

Foodborne Illness and Symptoms

Foodborne illness or food poisoning happens when a person gets sick from eating foods that are contaminated with microorganisms like bacteria, parasites or viruses. Botulism is of particular concern for packaged, unrefrigerated mushrooms that are labelled “Keep Refrigerated.”

The most common symptoms of botulism include:

• Nausea
• Vomiting
• Diarrhea
• Fatigue
• Muscular weakness

It is estimated that there are approximately 11 million cases of food-related illnesses in Canada every year. Many of these illnesses could be prevented by following proper food handling and preparation techniques.

What is the Government of Canada doing about the safety of fresh produce?

The Government of Canada and industry work together to help identify best practices that can be used to help prevent contamination of fresh produce throughout the food system, from the field to the store. In addition, inspection and enforcement activities conducted by the Canadian Food Inspection Agency work to ensure that steps taken by producers, manufacturers and importers have been effective and that the foods available to Canadians are safe.

Additional food safety information can be found on the Canadian Food Inspection Agency ,  Be Food Safe and Canadian Partnership for Consumer Food Safety Education Web sites.