Quick Guide to Prototyping
As we have learned in Production Techniques, mycelium can be grown in any number of ways. These techniques vary in necessary resources, applications, equipment, and skill level. In order to make the foundations of working with this material as accessible as possible, Mycopedia has put together a quick guide on how to make molded mycelium parts. This guide has an emphasis on low-cost materials, minimal equipment, and an easing of the learning curve. This guide will focus specifically on growing mycelium in molds, but the general techniques will apply to other methods as well.
First and Foremost, it is important to understand your two greatest constraints in growing mycelium: time and contamination. Mycelium is an organic material, and thus needs time to grow. Depending on scale, a part can take anywhere from two weeks to a month to grow to the proper density. When designing a mycelium prototype, front-end time management is essential. In order to begin growing, you must first have the proper amount of time to grow. When working around due dates for project, you should always account for at least two to three weeks for growing.
Contamination is a constant threat, but can largely be avoided through proper technique. Contamination in this context specifically refers to other fungi (Ttrichoderma; commonly called “Ttrich”) growing on your mycelium or substrate. This not only invalidates the structure and visual quality of your parts, it is also actively decomposing and destroying your part. While many projects fully intend for your part to be decomposed, this shouldn’t occur while it is still growing. Contamination is best dealt with preventively. Once a part is visually contaminated it is too late. It should be thrown out, or at least placed far away from any other mycelium you are growing to prevent cross-contamination.
A majority of the labor in dealing with mycelium is preventing contamination. With the proper approach, this is straightforward task. The most likely thing to contaminate your mycelium is your own body. The human body is covered in bacteria— breathing directly on your mycelium, or touching it with your bare hands is sure-fire method for contamination. To combat this, all work with mycelium should be done with a surgical mask and nitrile gloves on. Ideally, you should wear tight-clothing and tie-up long hair. While it is near impossible to have a sterile environment outside of a lab or proper farming set-up, Isopropyl alcohol can help to disinfect your environment. It is important to use 70% Isopropyl alcohol as it is more effective at disinfecting than 90%. Before working with mycelium, you should use isopropyl to clean your gloved hands, forearms, and any surface you are working on.
As briefly covered in Nutrients & Substrates, the basic technique of growing mycelium is simple. A substrate is pasteurized to remove potential competitors and contaminants, then inoculated with grain spawn. Mycelium is then grown, packed into molds, placed in a bag and forgotten about in room with the proper temperature for growth. We will break down this process step-by-step, and provide insights on preferred conditions for growing. This guide will feature many hypertext links, which can be consulted for further questions.
The first consideration to make is to decide what substrate you will grow on. For this guide we will be only be using Oyster mushrooms, which grows well on many substrates. However, we will focus on straw, hemp hurds, or paper products as the ideal candidates. These substrates are low on nutrients, meaning there is less competition. This allows us to simply pasteurize our substrate rather than sterilize. For more information on how to prepare sterile high-nutrient substrates (sawdust, wood chips, and soy bean hulls) we recommend FreshCap Mushroom’s guide to sawdust block production.
Substrates can be pasteurized through heat, pressure, and/or pH. We have found using pH to be the least labor intensive method with the lowest chance of improper technique. Pasteurizing through pH requires raising the pH of a substrate till is inhospitable to contamination. Oyster mushrooms are uniquely capable of growing in high pH enrichments and we use this to our full advantage.
To raise the pH of a substrate, we soak the substrate in lime-water. Limewater is caustic and should be handled with extreme care to prevent injury. During this phase, you should wear gloves, a mask, and safety goggles. In the case of spilling limewater on yourself, you should be prepared to wash throughly with soap and water. If it spills onto your clothes, that item of clothing should be removed and washed.
To create limewater, we will dissolve pelletized or ground hydrated lime into water. It is essential to buy Hydrated Lime, rather than gardening lime. In order to drastically raise the pH we need the high amount Calcium Hydroxide present in hydrated lime. We recommend this brand of lime, available at Lowes in small quantities. The limewater we used is mixed at a ratio of 6 grams of lime to 1 gallon of water. To prepare this, measure out 1 gallon (or up to 3 gallons) of cold tap water into your 5 gallon bucket. Using a kitchen scale, measure out the proper amount of lime (6 grams per gallon). Pour this lime into the water, and allow it to soak for a few minutes. Then, using a large stirring utensil (we use a scrap 2x4 piece of wood), stir and grind the pellets until fully dissolved.
Once dissolved we can add our substrate. The measurements here are irrelevant as long as there is enough water to entirely cover your substrate. It is possible to calculate out the exact moisture percentage for your substrate, but as long as there is more water than the substrate can absorb it will work. With gloved hands, thoroughly mix your substrate into the limewater. Once it is mixed, and no part of your substrate remains dry, use mesh screen or chickenwire cut to the size of your bucket to submerge your sublate in the limewater. Then use a heavy, non-porous object to weigh down the screen. We use a clean, large rock from our backyard. To allow your substrate to soak, leave it in this bucket for a minimum of 12 hours and up to 48 hours.
Now that your substrate is properly soaked and pasteurized, we must drain off the excess limewater. Using a roll of screen mesh clamped over a large sink or suspended outdoors, carefully pour out the limewater and then the substrate onto your screen. Allow your substrate to drain for at least 20 minutes. Once again, you can calculate the exact moisture percentage of 60%, but we recommend “feeling out” this moisture using field capacity. Field capacity is the range of moisture where a substrate has absorbed the maximum amount of water holding without any excess water. To do this by hand, grab a handful of substrate and tightly squeeze. Droplets of water should fall from your knuckle and palm. If streams of water come out, your substrate needs to continue to drain. The video below is a visual example of proper field capacity. The substrate should ultimately be damp, but not wet enough to pool water. The substrates mentioned in this guide are very forgiving, but a substrate that is too wet can lead to slow growth and sometimes contamination.
When your substrate is properly drained, it is ready to be inoculated with grain spawn. Please consult our supply list to see options for purchasing grain spawn. When handling your grain spawn it is extremely important to be as clean as possible. We prefer to measure out our spawn with fresh set of gloves. Apply isopropyl to your gloves, forearms, and any table or surface you are working on. Wearing a face mask at this point is essential. Grain spawn can be measured by weight, but we prefer the simpler measurement of volume. When farming mushrooms for peak yield, a ratio of 10% of grain spawn to the total volume is common. For growing mycelium, we often use a higher ratio to encourage quick and dense growth. We typically use a 20-30% ratio of grain spawn to substrate. [EX: For a part that uses 1 quart of substrate, we would use a cup of grain spawn] To properly measure the grain spawn volume, break up the grain spawn into a bowl. Using your hands to crumble the spawn, try to break it into as small of chunks as possible. Each of these grains are a point of inoculation, where the more it is spread out evenly into the substrate, the better. From this bowl you can measure out the correct volume. Once you have become accustomed to the proper ratio, you can get away with eyeballing this step.
There are two techniques for adding your grain spawn to the substrate. One option is to thoroughly mixed the two together in a separate container and then pack your mold. We have found that this often results in the smaller pieces of grain spawn falling to the bottom and making inconsistent mixtures. However this is not totally unacceptable, and will still result in growth. Alternatively, we prefer to pack our molds and bags in layers. First laying down substrate, we sprinkle grain spawn on top of this layer evenly. We continue to alternate between layers of substrate and spawn until our mold or bag is full.
If you are concerned about contamination, we recommend growing your mycelium in a grow bag first. These bags have micropore patches to allow for air exchange while limiting contamination. After a week or so, once the bag is covered in dense, white growth, you can break this mycelium up and pack your mold. The mycelium will be able to regrow itself to the form of your mold and there is less concern about it becoming contaminated. Again break this mycelium into small chunks.
Before packing your mold, you should give it a brief wash with isopropyl. There are many techniques for mold making, but ultimately the mold should be non-porous and easy to remove once the mycelium is done growing. For this reason, clear plastics are ideal. In our lab, we primarily use 3D Printed PETG molds. When packing your mold, the substrate should fill the entire mold but still have plenty of air and room to grow. If you pack in your substrate too tightly, you risk suffocating the fungi.
Once your mold is packed, place it in a sealed ziplock bag. If you a growing a larger part, use a garbage bag but be sure to seal the opening by tightly wrapping it with a rubber band or zip-tie. This bag will protect the part from contamination and maintain the high humidity ideal for strong growth. If your mold has thick walls, the bag may not be necessary.
One of the most difficult parts of this process is to step away. Despite any of your intentions, it is best to leave your part in this bag unopened. Any time you open the bag, you are actively risking contamination. Clear bags are ideal to allow you to observe growth from a distance. This growing stage normally take two weeks, and during this stage it is essential to step away and allow it to grow. No matter what anxiety chips away at you, resist the urge to open the bag.
Once your part has grown for at least two weeks, you can open the bag and de-mold. If the surface finish or density of mycelium is less than preferred, you can place this part back in the bag and allow it to grow without the mold for another week. This method external growth results in parts with much denser, but less controlled growth.
Behold, your mycelium part in all it’s glory. Your part will be delicate, wet, and covered in soft mycelium. This part is alive and will continue to live until you allow it to decompose or “bake off” the living mycelium. By baking your part, it will shrink in size but become much firmer. A majority of mycelium applications require it to be baked to get the most out of the material. To bake off your part, apply low heat for as long as possible until it is bone-dry. A common method is to use your oven on its lowest setting, rotating the part if possible. In our lab we use a modified food dehydrator. During the summer, simply setting the part out in the sun for several days also works. There are many guides claiming exact temperatures and times to bake your part, but these variables are highly dependent on your own specific part. We recommend baking your part until it is completely dry tactilely or as dry as the substrate you started with.