Alternative substrate pasteurization for high effeciency oyster mushroom growth

Mushroom cultivation is increasingly being incorporation into gardens, home food systems and permaculture systems. By providing simple workshops, we have tried to make this more accessible to new growers. It has also been a fun way to attract a very energetic and younger group to engage with our permaculture community. Oyster mushrooms (Pleurotus ostreatus) has been the “gateway” fungus for new growers and remains the largest share of our own year round production.
Finding simple methods of pasteurization can make this easier for new growers. Pasteurization methods for substrate have been fairly well documented although some of the specific details are left to the grower. Hot water methods are the most common, and we have used them extensively for indoor growing. However, we have been very impressed with the ease and potential to convert a waste product to building material with the alkali or lime method. In summer, we grow Oysters from a stack of totes with holes in the side, and we will probably experiment with alkali pasteurization for bag culture. The resources and documentation for growing at http://www.alohaculturebank.com/low-tech-growing.html#.Vep6I31RYXg has many other details on this and other method. But what follows is how we do this for our small scale operation. This can be scaled up or down but the proportions should work.
The best biologic efficiency (BE) has been with calcium hydroxide (builders lime-NOT TO BE CONFUSED WITH AG LIME) 1.5 kg and 1 kg of wood ash for a 55 gallon plastic barrel. To allow use of the lime, the barrel is filled half way with water and two burlap coffee bean bags stuffed with chopped barley or other straw can be forced in and usually persuaded to sink with several cinder blocks and a lot of cursing. The straw is left overnight in this extremely alkaline solution. The not very accurate pH paper measures a pH of 13, but once the straw is dumped and drained the pH reading drops to about 8-9 and is ready to mix with grain spawn. One barrel can fill about 3-18 gallon totes, so it is close to the total volume of the barrel that is treated. The coffee sacks keep the straw from sticking in the lime at the bottom of the barrel. Pasteurization can be done with lime alone, but the tests by Aloha show increased BE with wood ash, especially with a lot more than we use. The residue may be a useful produce, potentially as lime putty. Wood ash up to 20% added to lime can increase the strength of lime and increases workability but may decrease frost resistance. Leaving out the wood ash may reduce BE but allows more flexibility for the use of the lime putty. There is still a large volume of alkaline solution to dispose of and this requires some thought and assessment of the appropriateness to the site. As an over bearing elder, I must remind new growers that the lime solution is very caustic and rubber gloves, protective clothing, protection for eyes and a ready source of clean running water if the worse happens is responsible practice.
So for others working to develop more appropriate small scale processes this may be a pasteurization system that generates a potentially useful byproduct for use in building. However, one of the best byproducts of growing and sharing mushroom knowledge has been friendships with a younger generation that we would not have met. We are counting on some of this group to provide affordable spawn and expertise, as we plot diabolical schemes for spreading mushrooms in permaculture and permaculture in Alasksa.

I'm impressed. If this works well growers will save money on their gas bill.
Only barley straw that is tested?

The lime pasteurization appears to work on a wide variety of straw or straw-like substrates. Barley is the only straw that is grown locally in our region. Wheat straw has been used commercially. Other diverse high-cellulose materials have been used in Africa with this method. There are some large commercial mushroom farms in the US that are using this method to prepare substrate. These producers are probably using a pump system to sprinkle the lime solution over a large quantity of straw. Some of this is probably viewed as “trade secrets” of the growers.

The energy utility of this system would occur if the lime putty that remains at the bottom of the barrel can be used for building purposes. Then the function of pasteurizing is essentially free, since the building material is almost completely recovered with only the soluble material lost. Energy is artificially cheap in the US and propane may still be the cheaper method. It is the increase in biological efficiency that is intriguing, and this impacts the final cost of production as well. The alkali may be making more of the substrate available by dissolving hemicellulose or cross linking of protein as occurs in nixtamalization of corn/maize. If the lime is not used as a substrate, then the embedded energy and carbon footprint in making the lime is probably higher than occurs with water bath pasteurization.

So this is another place where “stacking” functions can lead to a new product with little added energy.

hau, Christine, I have a lot of hardwood ash which I use for leaching out lye.
I am going to try your method sans the lime (in my case the putty would be more of a waste product I don't build anything where it would be of use to me).
The lye I make from the hardwood ash comes out at a pH of 13.8 so it just may work similar to the lime you are using.
We have access to lots of wheat and oat straw, which we use for straw bale garden beds and animal bedding.
I can get burlap sacks from a coffee company that imports their own green beans so this method is very doable for us.
I will post here how it goes.

Thank you for sharing this method, we are just getting started in growing our own mushrooms.

Hi Bryant, should be interesting. Looking forward to your results. Please check the pH before and after pasteurizing. You might consider adding gypsum after pasteurizing. We use about 1/4 cup for 1 bale (5% is recommended). It is supposed to improve yield. Also, if you are looking for inexpensive spawn, consider Official Mycology Classifieds on FB. Great deals, good advice,and lots of different cultures available for small labs for people who love growing fungi. Good luck!

I have had marginal luck with lime and sawdust. I need a new grow area to see if the problem is the pasteurization or later contamination.

R Scott wrote:I have had marginal luck with lime and sawdust. I need a new grow area to see if the problem is the pasteurization or later contamination.

It is impressive that you have had any success with sawdust and calcium hydroxide! What mushrooms were you growing? Sawdust is such an unforgiving substrate compared to straw. Mushroom strains can be very finicky about the origin of sawdust, and I seem to always have a battle with competing trichoderma, even with sterilized substrates. Trichoderma spores would almost certainly survive the alkali treatment. It seems that high energy input methods of full sterilizaton under pressure or with very long cycle steam processing is still the most effective for sawdust. Stropharia may be the exception. Once it starts to run on a dirty complex substrate, it is probably the trichoderma and anything else in it's way that becomes part of the mushroom.

Wow! I love it! I grew oysters last year on a sawdust/wood chip medium that I hot water pasteurized. It worked for a small amount, since I can only reasonably boil a few gallons of water at a time.

I would be excited to upscale oyster production with less labor by using lime and wood ash. Thank you for sharing!

This seems like a lot of trouble to go to. I've done oysters twice, both times by what Field and Forest calls,the totem method. We cut a tulip poplar in March and slice it into pieces between 6 and 12 inches in diameter and height. Let them age a bit, then put a cupful of sawdust spawn in a large black plastc bag; add another half-inch of sawdust spawn and another round of wood. top it off, or add a third piece if it's stable and you want to. The uppermost one gets a final half inch of spawn, then a large paper bag is upended over the top. If you can't find one you tie newspaper about the top. Close the bag, leaving a little air gap, and let it sit about three months at roughly room temperature (the second time we had chilly nights in the forecast so I found room in the house for these). After about three months they should be visibly full of white or cream colored mycelia. Move them out into the woods, only one high now, in a shady place. Keep them watered if it's dry. I set them on old boards because when the mushrooms flush, they tend to do it around the top and bottom rims so setting it on a board reduces the time spent picking leaf bits and twigs and dirt out of the mushrooms. Both times I did this in spring, got a good load of mushrooms in late fall and another in spring, and then a small flush the second fall.