Understanding Contamination and Its Causes:
Contamination refers to the unwanted invasion of harmful microorganisms during the mushroom cultivation process. These intruders can originate from the environment, our hands, spore syringes, or even contaminated substrates. Understanding the causes and errors during cultivation can help us prevent contamination effectively.
1. Contamination during Inoculation:
Inoculation is the phase where mushroom spores or mycelium are introduced into the growing medium; AKA the stage when you introduce your syringe into your grain. Contamination can occur in the following ways:
a) Improper Sanitization: Failure to sterilize equipment like syringes, needles, and growing containers can introduce contaminants into the substrate. You should do everything possible to decrease the chance of external contaminants entering the workspace and sanitize existing contaminants. For disinfection, 70% ISO is the go-to; Do not buy 90% or higher. The higher concentrations of alcohol evaporate too quick to effectively destroy bacteria and contaminants, thus rendering your effort useless. 70% gives time for the sanitization to do its magic before evaporating. You can seldom have too much ISO in your workspace; It can be annoying if everything is wet but it’s a good guarantee no bacteria is left behind. I recommend an ultra-fine mister and filling it with ISO; It makes sanitization a breeze.
b) Contaminated Spore Syringes: Using spore syringes that have been improperly handled or stored can lead to contamination. This is rarely the consumer’s fault. It is important to get your cultures and spores from reputable sources that test regularly and transfer when contaminants have been detected. You can utilize agar to test your cultures and spores and inspect for growths other than mycelium; Indicating contamination. Nine times out of ten if you order from a trustworthy vendor, your culture will be clean and you can even utilize something like an LC expansion jar to grow it and have plenty of clean, strong mycelium.
c) Poor Hygiene: Not thoroughly washing hands before handling the substrate or equipment can introduce contaminants. This one is also not a common issue, but it needs to be said. Take a shower before doing sensitive work like inoculation or transfers; It takes a fraction of the time it would take if you have to redo the grow due to contamination. You don’t have to go overboard, just be clean.
2. Improper equipment and preparation
It is essential you build or order high-quality gear that will give your mycelium the best chance to grow. It’s no use in being sterile during inoculation if your grain jars have cracks and holes that are going to allow external contaminants in anyways. A little research goes a long way.
a) Improper Sterilization (Pressure Sterilization): Grain is not sterilized for long enough, hot enough, or at a suitable pressure. For one reason or another, if your grain is not properly sterilized then you will run into contaminants that were already present in the grain when you put them in the container. The recommended sterilization procedure for grain is 90 minutes at 15PSI; It comes out to roughly 250 degrees Fahrenheit. It is not harmful to go longer or slightly higher pressure; I usually recommend doing so for peace of mind.
b) Improper Hydration: Grains do not have adequate moisture content to encourage mycelial growth or in excess such it encourages bacterial growth. Too little hydration and your mycelium will not have the moisture required to expand and colonize further, essentially stalling it. Too much moisture will encourage bacteria, like bacillus, which will render the jar a total loss. The choice is grain can wildly impact how easy it is to get the moisture right; I find rye berries are relatively easy to hydrate and sorghum/milo being incredibly easy. Roaring boil on the stove for 10 minutes give or take is a good guideline, or until the hulls of your grain start to become transparent.
c) Faulty Equipment: Unfiltered air/contaminant entry into the grain. It’s important to routinely replace consumable equipment, inspect containers, and disinfect your setup to prevent contaminants through careless mistakes. A simple pinhole can be an entry for all types of mold into your jar if you were to use a self-healing port beyond recommended usage, for example. It’s not worth getting the one extra use out of a 5-cent piece of equipment. I use a flashlight to check all ports/lids/equipment for pinholes every so often.
Common Mushroom Contaminants:
Various contaminants can plague your mushroom cultivation efforts. Contaminants can also spread if left unchecked! When growing mushrooms on nutritious substrates, the grain and substrate are vectors for contamination and should be sterilized/treated as such. Unsupplemented substrates are generally a lower risk of contamination but being sterile is always recommended. Mycelium thrives when it is the only living body in the substrate. Here are a few commonly encountered contamination culprits:
a) Trichoderma: Emerald mold that thrives in warm and humid environments. It can overgrow mushroom mycelium and render it useless. Presents as a puffy white growth before sporulation in which it turns green and is a risk to any nearby grows. This one is usually fairly obvious but can be tricky to identify in species that bruise blue or other shades similar. Trichoderma can be tested with a Q-tip, which it will stick to when in contact. Bruising will not stick to a Q-tip. Most commonly caused by improperly prepared grain.
b) Bacillus and Bacteria: Foul-smelling and spongy growth that can lead to rotted and discolored mushrooms. Usually presents as yellowing or “ice cream” like texture. Most commonly caused by excessive hydration and lack of air exchange.
c) Cobweb Mold: A loosely used term to describe any fluffy/wispy and often grey fungal growths. This contamination is often identifiable from color and it often floats above the substrate instead of growing along it. Most commonly caused by improperly prepared grain and excessive humidity/lack of airflow.