Wednesday, May 3, 2017

Is Grain Spawn or Sawdust Spawn Better for Oyster Mushroom Production on Straw?
by Laura Kahles

From left to right: Italian, Golden and Pink Oyster mushroom growing on pasteurized straw.

I have been growing oyster mushrooms on straw for just over five years now. The opportunity to hand this task off onto other F&FP members has come up, but I just can't give it up. Why not, you might ask. My best guess...there is still so much to learn about this fascinating process. After five years, I still have unanswered questions, and more research to complete.

For anyone who is not familiar with the process, I will briefly explain. Chopped straw is pasteurized (cooked) in hot water to reduce the amount of contaminates it may contain (ie. molds, bacteria). After the straw drains and cools it is inoculated (planted) using oyster mushroom spawn (seed). After only a few short weeks beautiful oyster mushroom emerge, and can continue doing so for 2-3 months.

Here at F&FP our most popular type of spawn is called grain spawn. I use it when I can, but there are times when grain spawn becomes scarce here. The scarcity can happen for many different reasons including selling out, late grain delivery from our supplier, or equipment failures. When grain is in short supply I turn to the next best thing...sawdust spawn!

Which is better? I don't yet have a definitive answer to this question. As a professional I can see the good in both varieties. I can share with you what I do know at this point.

Grain spawn is easier to break up, and is easier to pour. A gentle massage of the bag will get the job done. If you have some pent up frustration I suggest you choose sawdust spawn. The oyster mycelium does a fine job of turning tiny sawdust particles into one solid brick that is easiest to break up with a firm fist. Do, however, be careful not to break the spawn bag.

Grain spawn breaks up easily, and adds extra nutrients.
Sawdust spawn has the advantage when it comes to spawn run time (time until full colonization). Grain particles are larger, and although they cover a larger surface area individually, there are not as many inoculation points as there are when sawdust is sprinkled throughout the straw. On average I have had mushroom pin formation two days earlier when using sawdust spawn.

Sawdust spawn is available in larger bags then grain, and it covers better allowing for more inoculation points.

Whether I use grain or sawdust I have gone to using a 5% inoculation rate. That is, 5% of the weight weight of the straw is the weight used in spawn. Bags of grain come in 4 lb. units and can plant about 4 sleeves (polyethylene 4 mil bags). Large bags of sawdust spawn come is 5.5 lb. bags and can plant 5 1/2 sleeves. If buying small quantities of spawn, sawdust ends up being the more economical choice. However, grain spawn requires buying a lesser amount of bags to receive our lowest price break. This makes grain spawn ideal for large scale commercial customers See the graphic below for our quantity discounting.

Now for the big question, which type of spawn produces more mushrooms? Remember earlier when I stated that I did not have all the answers...well, I don't have the answer to this just yet. I have seen some impressive numbers (in terms of yield) when using both grain spawn and sawdust spawn. On the opposite end of the spectrum, I have seen low yields from both types. Most of the time my diminished yields are due to other factors including (but not limited to) dirty straw, humidifier issues, or fungus gnats (there are many joys to mushroom farming).

My goals for the future are to do more comprehensive yield comparisons, and figure out which additives (if any) can help boost yield even further for sawdust and/or grain spawn. I will be sure to post results as soon as they are available. Stay tuned!

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