Cultivating mushrooms is simple in its essence but comes with its fair share of difficulties and challenges. Like any agricultural process, we are tapping into the life cycle of a complex organism and encouraging it to behave in such a way that's beneficial to our end goal - producing as much food as possible. Under the correct conditions, mushrooms will produce yields with more than 100% bioefficiency - the weight of the harvest will exceed the weight of the dry materials used as substrate. Before we get too deep into jargon, let's take a look at the basics of the process of growing mushrooms, starting from the very beginning:
The Substrate
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The substrate is the material upon which the mycelium feeds and colonizes. It provides the nutrition for the entire organism. Using organic matter and soaking it to increase the moisture content provides a viable substrate for most species of mushroom.
Straw is a common component of substrate, partially because it is cheap and readily available in most regions. In order to augment the nutritional content of the straw most growers will add another material. Some options include cotton seed, coffee grounds, or mesquite pods. The first step of the process is to create the correct ratio of straw to other organic material by weight. Then the substrate is soaked until roughly 70% of the total weight of the wet substrate consists of water. Many growers pack this wet substrate into gas-exchanging grow bags to be sterilized later. |
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Sterilization
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One of the greatest challenges of a mushroom grower is to minimize contamination. There are billions and billions of spores floating around just about everywhere, and if you don't want to end up with a bunch of unproductive slimy green or black bags of contaminated substrate you'll have to do your best to keep the majority of them out of the grow bags. These other spores will compete with the mushroom mycelium for the limited nutritional resources in the growing environment and decrease production, sometimes completely overtaking the mycelium.
Once the wet substrate has been packed into the grow bags, they can then be sterilized. Sterilization kills off all microbial life in the substrate, readying it for colonization by mushroom spawn. This can be achieved in a few different ways. The way to ensure the most comprehensive elimination of competing microbes is to put the substrate bags through an autoclave (seen at right) - essentially a big pressure cooker - which is used to sterilize laboratory equipment. Substrate can also be sterilized or pasteurized in bulk batches and then packed into grow bags, but this method is more susceptible to turning out contaminated substrate. |
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Inoculation
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After the substrate is sterilized it's ready to be inoculated with spawn. Ideally, this part of the process is done in a sterile or extremely clean environment. Each step provides opportunities for contamination.
A bag of spawn, usually grain that has been colonized by mycelium, is broken apart and added to the sterile substrate. In this way the mycelium is encouraged to continue to proliferate as long it has adequate nutrition and is not overtaken by other organisms. |
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Mycelial Colonization
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Now the mycelium just has to do what it naturally wants to: grow. At this point the bags don't need to be in a sterile environment, but the cleaner the better. They should be stored at roughly room temperature with as little fluctuation as possible. Humidity is not yet a concern since the wet substrate is creating plenty of humidity inside the grow bags. White strands of mycelium will start to form and grow, eventually covering the entirety of the substrate with a dense, white mass. |
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Fruiting
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Once the substrate has been fully colonized with mycelium the fruiting bodies start to form. The first appearance of what will eventually be full-fledged mushrooms is the primordium—that's it in the picture to the right. It looks a bit like clusters of tiny, leggy mushrooms —mostly stem and a very small but visible cap. Mushrooms take in oxygen and exude carbon dioxide. When they are ready to fruit they need an environment rich in oxygen. The air inside of the grow bag is dense with carbon dioxide, and the mushrooms want to be let out. The bag is slit 10-15 times with small holes for the clusters of mushrooms to grow out of. In a bit over a week the bags will be producing big clusters of mushrooms like the ones to the right. When the caps are flat but not yet concave they are ready to be harvested. |
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Harvesting
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The final step is the harvest. The clusters of mushrooms should be easily removed from the small slits in the grow bags, either by lightly breaking them off by hand or by slicing the mushroom stem where the fruiting body is emerging from the bag. Oyster Mushrooms are ready when the caps are quite large and have not quite turned concave. It's important to harvest before this stage, because as the mushrooms become concave they are preparing to drop spores. This is not ideal in a greenhouse setting as it creates an unsanitary environment and increases the chance of contamination. Weighing your harvest is extremely important because it allows you to establish bioeffeciency (BE). If the weight of the harvest after the mushroom bags have finished fruiting (usually 5-6 weeks) equals the weight of the substrate before soaking, BE equals 100%. If it does not equal 100% some troubleshooting is necessary, since most growers agree that 100% BE is necessary for a successful growing operation. Once the mushrooms are free of the grow bag and have been weighed, they should be stored at 50° F. They will keep for about a week without much decline in quality. Blue Oysters are the most durable of the Oyster varieties, but they should all be handled carefully. They're much more delicate and easily damaged that a Button, Cremini, or Portobello. |
This is just one way of many that a grower can successfully cultivate mushrooms. A grower need not go through all of the steps of this process to create a viable business - each of the various steps is a potential entry point. Many growers simply purchase bags already colonized with mycelium, fruit and harvest the mushrooms. Others pursue the microbiological aspects by running strains, and cultivating their own spawn.
Simply fruiting mushrooms from colonized bags in itself can be highly lucrative. In about 100 square feet of growing area, a grower can potentially produce 2,500 pounds of mushrooms a year (source). Even at a low wholesale price of $3 - $4, 2,500 pounds of mushrooms would generate a gross of $10,000. At the direct-to-consumer price of $8 - $10 (or more) per pound, this amounts to $25,000 or more per year - keeping in mind that this is for a grow space of only ten feet by ten feet.
Simply fruiting mushrooms from colonized bags in itself can be highly lucrative. In about 100 square feet of growing area, a grower can potentially produce 2,500 pounds of mushrooms a year (source). Even at a low wholesale price of $3 - $4, 2,500 pounds of mushrooms would generate a gross of $10,000. At the direct-to-consumer price of $8 - $10 (or more) per pound, this amounts to $25,000 or more per year - keeping in mind that this is for a grow space of only ten feet by ten feet.
