Oyster Mushrooms & Spent Brewery Grains

Oyster mushrooms (Pleurotus ostreatus) and it’s close relatives, being the generalist-adaptable type that they are, grow wonderfully from a wide variety of different substrates in addition to spent coffee grounds (which you can explore in my previous post on the subject right here). This time around I am trying out a few different modifications to my original method of culturing oyster mushrooms, the most obvious being the substitution of spent barley brewing grains instead of used coffee grinds, and wrapping a double layer of cheese cloth over the top of the mason jar in order to improve air circulation.

Unfortunately, the majority of the oyster mushrooms that started off so well in my previous posts did not make it past the 2nd or 3rd week. There were a number of different contamination issues, particularly Trichoderma harzianum, a green mold which can grow under anaerobic conditions and out compete the oyster mushroom mycelium, reducing future yields once the substrate is fully colonized. In order to remedy the situation, I decided to increase the air circulation and see if that will alleviate the problem at least a little bit. Because the mushroom start isn’t completely sealed off from the outside world, regulating humidity and moisture levels is now a concern. When I notice that the coffee grinds (or any substrate for that matter) are not glistening with moisture, I open the jars and spray them a few times using filtered water that I boiled and then allowed to cool to sterilize it.

So that is my rationale behind why increased air circulation might be a good idea. You will find out whether or not this adjustment is successful in one of my future posts on the matter. The focus of my article today however is introducing you to a new substrate: spent brewery grains. Grains, as well as pasteurized wheat straw, are traditional ingredients in commercial substrate mixes for oyster mushrooms and a few other different species. They work very well because they contain enough nutrient and cellulose (fiber) that the mycelium needs to grow strong and produce bountiful mushrooms. Usually various other additives are included in the mix to regulate acid/alkaline levels of the substrate and for added nutrition, but we aren’t looking for industrial scale efficiency here (or at least I’m not) and so for the time being I am going to skip those details.

Spent brewery grains, mainly barely or wheat, are a readily available byproduct of commercial beer production. Once germinated, mashed and boiled in water to make wort for the beer, the grains are ready to be disposed of. They could be composted, given away to livestock farmers (I know at least one brewery that donates their spent grains to a local pig farmer as feed) or down right thrown out, but that as we all know is tremendously wasteful considering you could also grow mushrooms in them. Like coffee, the grains are boiled and therefore sterilized when they are processed, so further sterilization (as long as the grains are stored in clean air tight containers or used almost immediately) should not be necessary. The spent grains that I used I saved from a past home brewing experience and frozen them. Today, when I began a new mushroom starter, I thawed the grains in advance and mixed them with my oyster mushroom cuttings following the same protocol as I always have.

So if you are interested in experimenting with other re-purposed mushroom growing substrates, give brewery grains a shot. If you live in southern Ontario, as well as most places in Canada or the Unites States, local craft breweries which use good quality malted grains are not something that you will have to try very hard to find. Give them a call or drop by their retail outlets and inquire about whether or not they can save you a bag of grain. Like coffee shops, breweries have to pay for their byproducts to be picked up and hauled away, so by diverting some of their grain you are helping them to save money. Just another fantastic reason to grow some mushrooms and go take a visit to your nearest brewery.



  1. Hi,

    Grain (malt) isn’t boiled in the brewing process, it is steeped in water at approximately 65 degrees C. Water, as you probably know, boils at 100 degrees C.

    The general recommendation for grain in mycology is to pressure cook it for 90 minutes or more depending on the size of the jar or bag of grain. You want to be sure you heat it right into the middle to sterilise it properly.

    If you want to make beer out of grain, I recommend you read ‘How to Brew’ by John Palmer. It is an online book that will give you a good rundown of the brewing process.



  2. As Sam said, in order to reach sterilization temps for use in cultivating mushrooms you need to pressure cook it at 15psi. Sterilization takes place at about 250*f. As we know boiling is done at 212*f. Also the more you open your container the more chances you have to introduce mold spores. Simply use a good filter such as tyvek or polyfill jammed through a small hole in the lid. cheesecloth is not sufficient to filter mold spores.I used coffee filters at first and everything always turned green. Keep up the good work and don’t give up.


    1. I recently took a mushroom cultivation course from Peter Mccoy (radicalmycology.com) and learned that not all mushrooms require sterilization for cultivation; Oysters are known to be one of these mushrooms- among many others- that only require the substrate to be pasteurized.


    1. Hey Matt. Thanks for your interest. Unfortunately I haven’t gotten the chance.. yet. There are other articles out there where people have added spent brewery grains (still warm from being used in home brewing recipes) to other pasteurized substrates as a nutritional amendment right before inoculating with spawn or mycelium. Brewery grains, because they are so nutritious, contaminate very easily and rather quickly so time is of the essence or if too much time passes then they must be sterilized again before being used for mushroom growing. I’ve been meaning to update this article and hope to get around to it soon, including the information that has been shared by other knowledgeable folks in this thread.


    2. Hey Matt,

      Thanks for your comment. Unfortunately I have not posed a follow up article. This particular experiment was unsuccessful for a number of reasons. I have been meaning to update this article with new information that I have acquired as to how to perform this technique properly but it’s currently on an exceptionally long list of edits that I wish to make on many of my articles.

      I suspect that my sterilization techniques were not adequate or that there was too much moisture left in the grain which resulted in the oyster mushroom mycelium failing to colonize. It certainly is possible to grow oyster mushrooms from brewery grains, although many other mushroom growers who I have asked/inquired to recommend mixing the grains with straw as they are very rich in nutrients and sugars, possibly too much and those conditions also make the substrate a perfect candidate for aggressive and rapid contamination from molds.



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