A lot of people like to shake or mix their grain spawn when it is 30 to 50% colonized, but 10% makes much more sense. If the grain bag is colonizing from a single location such as from the injection port or an agar wedge and you let it colonize to 30% – there were a significant amount of fully colonized grain touching other fully colonized grain: they basically do not contribute to the colonization rate.
If you could calculate how many pieces of grain on average, touch a single piece of grain, you could then opt to mix at that ratio, and once you did mix it – you could have a single fully colonized piece of grain touching uncolonized grain. All of these would be contributing to colonizing the rest of the remaining uncolonized grain.
So, how many pieces of grain is touching a single piece of grain?
We’ve done a small experiment where we soaked a single piece of grain in super glue, and placed it on top of other grain, then we buried it with more grain and gave it a gentle tap to emulate mixing the grain.
Our results show that, on average, a single piece of grain is touching 10 or more other pieces of grain. This would suggest that optimal mixing would occur at around 10% assuming you can properly break apart the colonized grain and mix it effectively and evenly through out the uncolonized grain.
there are a few types of contamination: bacterial, mold and yeasts. Understanding why you got a contamination in the first place can help you prevent it in the future.
bacteria will appear as wet spots, but not just any wet spot. It will be milky and runny. Water can form from condensation and it will be clear. Clear condensation isn’t contamination, just an artifact of the bag. Rarely you may also find starch that has been released from the grain
Left: bag is severely contaminated with a bacteria that produces heat resistant endospores. Notice the milky runny liquid that forms crescent moon 🌙 shakes towards the ground: this is bacteria that has settled in the droplets of water that form as it degrades the starches.
Right: sterile grain. Notice it is dryer but what moisture is present is clear and clean.
Above is an image of grain spawn that has colonized as well as accumulated a significant amount of water at the bottom. This water is crystal clear and a good sign the spawn is not contaminated with bacteria.
Bacteria will smell very off putting: sour is the smell that first comes to mind, or like the
Bacteria will degrade the starch in the grain which holds onto moisture. Mushroom mycelium and other organisms will also do this, but often these fungi are growing additional structures that can hold onto or utilize the water released better. Bacteria however seem to get suspended in the released water and float around with it, so the free water content in the bag will rise as the bacteria takes over and degrades the starches.
Bad Inoculant: Bacteria tends to occur either from bad inoculant that has the bacteria present, such as a spore syringe, LC syringe or already bad grain spawn that had bacteria present unbeknownst to the person inoculating the grain.
Improper Sterilization If it is not due to contaminated inoculant, it is from improper sterilization of the grain itself. Most simple heat treatments will quickly destroy the spores or actively growing forms of molds, fungi, and yeast as well as the actively growing forms of bacteria. However bacterial endospores are suprisingly heat resistant thanks to the stabilizing agent dipicolinic acid which makes up 15% of their structure. . As most bacteria isn’t spread via particles in the air, tends not to
Mistreatment of gas exchange filters More true with liquid cultures than spawn bags, but a wet filter patch that isn’t hydrophobic can fail and transfer bacteria into your substrate. This is common with homemade filters for liquid cultures, such as when micropore tape or tyvek is used. Unicorn Bags or other filter patch bags for mycological purposes tend to handle direct liquid contact better as they seem to have a filter made from hydrophobic layers of polyproplyene and teflon (PTFE), with very small pore sizes.
dust, fiber like structures, mycelium of different texture or structure, colors of white, green, red, black, brown, gray and tan.
Unlike a bacteria, or yeast these won’t have nearly as much smell, but they will have some mild differences from an otherwise fully sterilized bag of grain. Likely if the mushroom mycelium is growing, the smell of the mushroom will overpower the scent of most any molds.
Molds spread both by mycelium and by producing more spores rapidly. You may at first see it in a small localized area but if agitated it will likely spread its spores to other places within the bag.
Generally mold spores are easily and rapidly killed by heat, such as pasturizaton. So if you are getting a mold contamination, it is either from your inoculation or a failing component of the bag.
If you inoculated a bag of sterilized grain with a syringe, and the mold is growing where the liquid inoculant went; you likely introduced the mold by using a bad inoculant.
If the bag is not inoculated or it’s growing in a completely separate location, it is likely the bag has failed. The three most common ways are as follow:
1. Improperly attached or damaged filter patch. Improperly attached filters are fairly common due to the highly inert material the filter is made of as it doesn’t seal well with the plastic of the bag. This is often easly detected by squeezing the bag when it is inflated with air; if it rapidly loses its’ air with minimal resistance, check the filter. Alternatively there can be manufacting defects or other damages from handling that can add pin holes into the filter patch. A pin hole may seem small to us, but it’s a wide open door for many spores like trichoderma which have can a spore as small as 0.5 micron.
2. Improper seal An improper seal can form many ways and be deceptive. It may be sealed at too high of heat and result in small holes at the interface of the bag and seal, it may be sealed at too low of a temperature and only look sealed but failed to properly seal the bag; especially if it is a gusseted bag that four layers of plastic in some areas and two layers of plastic in other areas.
This can happen at both the top of the bag, or the bottom.
3. Improper handling of the bag Believe it or not, after you send a plastic bag made of one of the more rigdid plastics, polyproplyne, through a heat sterilization treatment, it can become somewhat brittle. If the bag folds in just the right way, it can form very sharp corners that are prone to forming tiny holes; either through being exposed to minor abrasion or just repeated bending.
Additionally, the gussets of a bag are prone to failure and will often fail where the fold meets the inner part of the bag. This is often due to some form of impact such as crushing or dropping the bag, but it can also happen in scenarios where you might have a substance hydrating and expanding inside the bag, a brick of coco coir with water added, or certain types of pellets in certain situations can expand and create enough force to compromise the bag.
Yeasts are fungi, but they behave much more like bacteria in this context. They are however easily killed off by heat and are not a sign of improper heat sterilization. They die well before the endospores even begin to die.
Yeasts alone will often look a good amount like bacteria, and will often have bacteria present. They contaminate bags often due to bad inoculate such as a poorly made liquid culture syringe, or improper inoculation procedures. They may present as white speckles but more often than not they present as an alcoholic or apple-esque vinegar type smell if bacteria is present.
Yeast contamination is often less common in my experience than bacterial or fungal as it most often involves using a bad culture than a bag failure and it seems to be over all larger, less mobile and less ressilant than molds or bacteria.
There are many ways to make sterilized grain, and each method has its pros and cons especially when considering the scale you are going to operate at. We will go over a few methods we find nice for the small grower, intermediate, and larger scale production.
Mix the correct amount of water and Sorghum grain together into the bag or jar of your choosing and pressure cooker for 90 minutes once up to temperature. When the 90 minutes is up, let it cool so it loses all of its pressure, is below boiling, and is at a temperature that allows you to handle the bags or jars. Operate the pressure cooker properly, and do not remove the weight until it is no longer under any pressure (once the safety lock drops).
Give the grain a tumble so that the bottom grain which is slightly more moist will mix with the slightly dryer top grain. Doing this while it is still warm to hot will aid in more even distribution of moisture, but ultimately this step is not needed.
Very easy process but be sure you get the water correct: too dry and it will be slow to colonize, too wet and it will have a bit of excess moisture. Both are generally okay but if you hit the extremes of too dry or too wet it can be problematic.
Here are our recommended amounts of water and Sorghum for this process in useful increments for jars and bags:
1 Pint Jars: 125 grams Sorghum 106 grams Water
1 Quart Jars: 250 grams Sorghum 213 grams Water
3 lbs Bags 760 grams Sorghum 650ml of Water
6 lbs Bags 1520 grams of Sorghum 1300 grams of Water
Sterilized Grain: What Grain Is Best?
For the production of mushroom spawn, Sorghum is probably the best choice.
The goal of grain spawn is to provide many points of inoculation, in certain circumstances nutrition that compliments the substrate, and colonize rapidly so that you can have a faster turnover.
In order to provide many inoculating points throughout the bulk substrate, you want a smaller grain as that provides, pound-for-pound, more inoculating points. A single pound of millet for instance will provide vastly more surface area and inoculating points than corn.
Not all grain spawn needs to provide nutrition; such as when growing oyster mushrooms on the master mix. The master mix has plenty and adding more spawn won’t be of much benefit beyond faster colonization times. Often times a large 5 lbs bag of master mix only needs a few tablespoons worth of grain spawn to colonize rapidly and perform well.
However, when growing Psilocybe species on CVG or other bulk substrate, the grain spawn provides most of the nutrition. Instead of a few tablespoons worth, the colonized grain spawn is in a ratio of 25% to 50% vs the bulk substrate. In this scenario, you’d want a grain that is high in protein, starch, and various fats and minerals.
The best grain is small, highly nutritious, cost-effective, and fast to colonize. We think Milo is the best option as it ranks well in all those aspects, but millet, rye, and oats are also great options.
Corn seems to be trending in the grain spawn scene but I don’t understand the logic beyond that it is visually pleasing when colonized.
Don’t overcomplicate it!
People love to get lost in the weeds with making sterilized grain, and there is a lot of misinformation going around. Some of the biggest misunderstandings come from the idea that the presence of excessive moisture, such as from condensation or burst grains leads to contamination. They do not, but they can make contamination more obvious. Excessive moisture and burst grains are annoying for many reasons; it can make it difficult to shake or break apart once colonized, but they do not cause contamination. Contamination comes from improper sterilization, faulty filters, or spawn bags that let contamination in. People will often see burst grains once they hydrate the grain and worry that it will cause big issues for them. If they have a good bag or jar and properly sterilize it, the grain will colonize just fine.
The same goes for moisture: even if you have perfectly and evenly hydrated grain, moisture can still form: taking it out of the hot sterilizer and into a colder room is going to cause the moisture to condense on the bag to some degree. This is resolved by letting it reach room temperature and tumbling/mixing the grain.
We recommend using a spore syringe or liquid culture syringe, but there are many ways to do so and the best method is always dependent on your situation, the scale you operate on and the equipment you have accessible.
Here is a quick description of how to inoculate our bags using two different methods:
How to Inoculate Sterilized Grain Bags With a Syringe
Be it a liquid culture syringe or a spore syringe, all you need to do is wipe the injection port with an alcohol wipe and quickly but carefully inject the sterile needle into the injection port that comes built into our sterilized grain spawn bags. While it is best practices to do this in a clean room or a Still Air Box; it will work far more often than not in a room, a dusty garage, or anywhere else. This is only true for this method. The moment you cut open the bag to add an agar wedge or grain to grain, you absolutely need a Still Air Box at a minimum, or a Laminar Flow Hood.
if you are reusing the syringe, quick and gentle flame sterilization can be helpful but be warned: shoving a glowing red hot needle into the bag will likely damage the self-healing properties of the injection port.
Another thing that can be harmful to the injection port is aggressively moving the needle in multiple directions. Just inject it, squirt it, and pull back. You can always tumble and mix the sterilized grain bag once it has been inoculated.
How to Inoculate With Agar Wedge or Grain to Grain (G2G) Transfer.
In a very clean area, such as a Still Air Box, or in front of a large laminar flowhood, prepare your area by wiping everything down with a disinfecting or sanitizing cloth. This includes the the bag, your hands that are gloved, and the impulse sealer. The impulse sealer is an absolute must; you cannot effectively close the sterilized grain bags otherwise and expect them to be fully protected from mold spores that are suspended in the regular air.
Carefully cut open the bag by a sterile razor or other cutting instrument; we like to use a sliding paper cutter similar to this one as it provides a clean straight cut as close to the top of the bag as desired.
Separate the bag so that it is open, be careful never to put your fingers or any other device inside the sterile grain bag: it isn’t needed and will only increase your risk of contamination. Carefully and cleanly drop your colonized grain spawn or agar wedge into the opening of the sterilized grain bag and then close it, then seal it with the impulse sealer. Working fast but not clumsy is helpful, but if you ensure that you have good sterile technique and a proper clean setup you don’t need to act too fast.
By far the easiest mushroom to grow at home is the oyster mushroom. It’s popular as a kit, kits are ready to fruit once holes are cut into the bag and placed in a humid location without much airflow, that would otherwise dry it out. Small kits are highly commercialized, and available at walmart, home depot and other similar stores.
However, if you’d like to grow oyster mushrooms in a more economical way, on a sizable scale, kits can be too expensive unless you have a good cheap bulk source of ready to fruit blocks.
A good option to grow at home is to use wheat straw; it can be used to grow large quantities of oyster mushrooms without any additional supplementation and without any heat pasteurization or clean work. Heat pasteurization can often be difficult to manage and dangerous, and clean room work can be an expensive barrier of entry to new mushroom growers.
Materials Needed To Grow Oyster Mushrooms on Straw
1. Wheat Straw – ideally shredded. Wheat straw is often smaller and easier to shred and manipulate than barley or other straws, but these will work as well. Pre-shredded wheat straw is often available at Tractor Supply, but it is much more expensive than baled straw.
2. Hi Yield Hydrated Lime – this is a pasteurizing agent and is often available at garden supply stores. Other products also called lime will not work if they are not low magnesium calcium hydroxide.
3. Water – This, combined with the hydrated lime, will hydrate and pasteurize the straw, getting it ready to be inoculated with oyster mushroom spawn, or a kit (either before or after the kit has fruited; so long as it looks healthy)
4. Soaking & Draining Container – this is to let the straw hydrate and pasteurize in the hydrated lime solution. as welll as let it drain once fully hydrated which takes approximately 24 hours to soak, and an hour or two to fully drain.
5. Bag or Container for Colonization – This could be 5 gallon buckets with holes drilled in them, large durable plastic bags, or anything else that can hold a few pounds of hydrated straw.
Steps to Grow Oyster Mushrooms on Straw
1. Get shredded wheat straw – this can either be purchased at places like tractor supply or you can buy bales of straw from a farmer and shred them yourself. This can be extremely messy, and isn’t absolutely needed, but shredding the straw significantly increases yields and makes for a better more compact substrate that is less likely to have problems and colonizes faster.
2. Add and compress the shredded wheat straw into your soaking container. Make sure your container has a means to drain or is small enough that you can easily pour off the water without the straw going with it. You will want to let the straw drain until no more water comes off of it, so make sure it has a sieve or a good drain on the bottom. You will also want something that can hold down the straw so it is fully submerged during the soak.
3. Dissolve hydrated lime in water. Add enough of this solution to completely submerge the straw, again, having something to weight down the straw is a good idea to ensure all of the straw gets properly hydrated and pasteurized. Exact amounts of lime is difficult to provide but 330 grams per 50 gallons of water is the generally recommended. More is often better as excess will be poured off with the solution. That said, as long as the solution is strongly basic and remains strongly basic throughout the soaking process it will work well.
When we do it, we use a 55 gallon drum, and use a pump at the bottom of the barrel to recirculate the water and lime mixture.
There is a circular hose at the top with many holes drilled in it to help the lime mix properly by circulating it from top to bottom, and distributing it over the top.
It is better to mix the lime with the water before hand to ensure even mixing unless you have a setup similar to this. The pump also doubles as a means to drain the solution from the 55 gallon drum so that it can be manipulated more easily.
Once the straw has soaked for ~24 hours, and has fully drained, we pour the shredded straw on a clean tarp and add spawn. We’ve used as little as one spent 5 lbs straw oyster log from previous cold pasteurization or a single 3 lbs bag of colonized grain spawn with great success, but we normally use a lot more colonized grain spawn as we are a company primarily focused on grain spawn, so we have a lot of it in excess. Grain spawn is nutritious and adding more will increase yields and decrease contamination rates and lead to faster colonization and fruiting of the substrate.
4. Mix prepared straw with oyster spawn – oyster spawn can be purchased and used, or even smaller grow kits can be used to inoculate straw by breaking them up. A grow kit that has already produced fruits but still looks healthy is a great option so long as it is free of obvious contamination such as other unwanted molds. The better the spawn is broken into small pieces and evenly distributed through out the straw, the faster it will colonize. More grain spawn is better as it will provide faster colonization and additional nutrients but we’ve had great success with 4% grain spawn by weight.
5. Place straw and spawn mix into the container which it will fruit from. This could be anything from large ziplock bags, trash bags, 5 gallon buckets, or even very large polytube bags that are 5+ feet tall and 1ft in diameter.
Here are pictures of two vastly different sizes of oyster straw bags.
6. Ensure container has holes for fruiting, approximately every 5 inches over it’s surface. This is important or the oyster mushroom to properly colonize, and for the mushrooms to grow, as they will grow out of these holes. Hole size can vary a good amount ranging from a dime sized hole up to a cut the entire length of the bag. The colonizing substrate needs to breath in order to colonize without contamination. A filter patch is often less ideal than cutting holes. The holes provide air exchange as well as a location for the mushrooms to grow out of the substrate for harvesting.
This is a polytube bag approximately 2.5 feet tall and 1 foot in diameter. Various holes were cut to let the oyster mushroom breath as it colonizes. Oyster mushrooms will grow out of these holes once it has consolidated.
Shredded Straw VS Regular Unshredded Straw
One might be tempted to skip using shredded straw and instead opt to use straw straight from the bale in hopes of reducing labor, machinery to shred the straw and to avoid the messy dusty nightmare that is inexorably linked to shredding straw. But, shredded straw has significant benefits both on yield and density of substrate which translates to being able to grow more mushrooms in the same amount of space. This study: Simplified and Lower Cost Methods for Culinary-Medicinal Mushrooms Cultivation shows that shredded straw can have 4 times the yield as unshredded straw; going from approximately 40% to 170% biological efficiency. One 50 lbs bale of straw can yield 85 lbs of fresh oyster mushrooms if it is shredded, but may only yield 20 lbs if it regular not shredded straw.
Images of Oysters Grown on Lime Pasteurized Straw
Have questions about this process? Just ask!
If you’d like to grow oyster or other mushrooms and need any help or further guidance, please reach out to us.
We would be happy to walk you through anything from a small personal grow using straw or help you hone in a larger commercial project that uses master mix or other supplemented sawdust.
You can get direct help by texting 435-237-2998 or emailing Cameron@spawnmagic.com