Mushroom Substrate

Inputs & Substrate Considerations

The microbial quality of what mushrooms grow on can make the difference between having a successful crop and not having any crop. In many cases, mushroom substrate is a mixture of animal manure and other ingredients. If that substrate isn’t treated and handled in a manner that reduces the potential of foodborne pathogens, the mushrooms you grow from that substrate could be contaminated. If you use sawdust or other types of substrate that are not transported or stored in a manner that prevents pests from getting into the product, what they leave behind in that substrate could cause a foodborne illness outbreak. There are a few things that can help you prove due diligence with respect to the substrates mushrooms grow on.

Supplier assurances. It is impossible to mind-read how your substrate supplier cares for their product. It is important that you ask them to share the information, in writing, to verify their practices. The act of asking for a supplier assurance helps them better understand your needs. If a supplier refuses to provide an assurance letter, this might be a red flag to find another supplier. The Produce Safety Alliance offers a model template Certificate of Conformance for compost suppliers that can be a helpful starting point to tweak to mushroom feedstock assurances. You can download it here.

Validation and verification of in-house pasteurization. Many mushroom growers pasteurize their substrate in-house. If you are a person who does this, you should use a validated process that specifies a time and temperature combination to adequately reduce the pathogens in the substrate. Penn State University offers one such validated process for mushroom growers. It’s also important to verify that the time and temperature were achieved. For reference, when you validate something, you are asking, “Am I doing the right thing to control pathogens?” and when you verify, you are asking, “Am I doing the validated process right?”

Making an appropriate substrate for growing mushrooms is equivalent to the composting process. For the FSMA Produce Safety Rule, if you were making compost in-house, you would need to document time and temperatures. Similarly, when creating substrate, you must record heating time, temperatures achieved and who did the measurements.

If a grower would like more info about practices to comply with the FSMA Produce Safety Rule or writing a food safety plan, they are encouraged to reach out to their local produce safety technician or MSU Extension. If they have difficulty tailoring GAPs to their farm, they are welcome to contact the Michigan State University Extension Agrifood Safety Work Group at gaps@msu.edu or (517) 788-4292.