Contamination Causes
Contaminated Inoculant:
Contaminated Liquid Culture - most or all jars inoculated with liquid culture usually shows the same contaminant. Make sure to purchase from a reputable dealer that stands by their product.
Contaminated Agar Agar - can easily be isolated but careful monitoring and a keen eye is required or transferring contamination to grain spawn is possible. It is important to follow appropriate steps when conducting Agar Agar Transfers.
Symptoms: Mold or Bacteria in Substrate or medium, slow colonization, or funky odor
Botched Inoculation:
Things that can contaminate an inoculation include: touching a needle, scalpel, or inoculation with something that isn't not sterile, touching the sterile inside part of a jar with your gloves, exposure of sterile items to airborne contaminants, moving unsterile item over sterile areas, or moving unsterile items between the filter and sterile while using a flow hood.
Symptoms: Mold or Bacteria in Substrate or medium and will stall (nothing will grow) spawn run.
Botched Grain to Grain Transfer:
Similar causes to botched inoculations. The contaminant typically does not show up until the grains have been spawned. Contaminated grain-to-grain often lead to a large number of bags becoming contaminated. Ideally work is always down in-front of a HEPA Filter Laminar flow hood. Grains should be checked for odors before spawning. If Mason Jars are used, It's particularly important that jars and lids be disinfected as the vibrations created during the transfer can easily shake loose contaminants.
Symptoms: Mold or Bacteria contamination, slow colonization, or funky odor.
Insufficient Sterilization:
When sterilization temperature and time are not adequate bacterial contamination may occur. The bacteria is usually widespread in the substrate appearing days to weeks after the “sterilization”. It's important that steam fills the entire pressure cooker/pot before you start timing the procedure. It is also important to note that sterilization occurs when internal temperature of the substrate reaches 121 Degree Celsius or above.
Additional Factors that affect Sterilization Time:
Larger substrates containers require longer times for the heat penetrate to the center.
Whole grain jars contain a lot of empty space between the grains which slow down heat transfer.
Symptoms: Substrate can show signs of contamination before inoculation, inoculated blocks will show signs of contamination early on during spawn run. Will also cause lower mushroom yields.
Filter Patch or Bag Failure:
When the Filter Patch becomes damaged or wet.
Bag is punctured or ripped.
Symptoms: Contamination can occur if the substrate isn’t fully colonized.
Improper or Cross Contamination during Pasteurization:
Pasteurization temperatures range from 63 to 72 Degree Celsius. The lower end requires a minimum of 30 minutes, while the upper limit requires holding for 15 seconds.
When spawning it's important to limit exposure of the spawn grains and pasteurized substrate to contaminants.
Hands, clothes, and hair are major vector for recontamination of pasteurized substrate.
Cooling substrate should be protected from dust as much as possible.
Symptoms: Mold during spawn run or later flushes (Lower Mushroom Yield).
Insufficient Free Air (O2) Exchange:
A lack a Free Air Exchange while bulk substrates are colonizing creates anaerobic conditions which can stall the recovery and colonization of the mushroom mycelium and promote the growth of anaerobic bacteria. A fermentation odor may develop. In serious cases the mushroom mycelium does not recover.
Mushroom Mycelium performs cellular respiration to convert oxygen and glucose to carbon dioxide, water, and energy.
Symptoms: No Growth/Stalling, bacterial contamination, and odor.
Insufficient Cooling or High Temperatures:
Make sure pasteurized or sterilized substrate is adequately cool before inoculation.
Elevated ambient temperatures can yield to mushroom mycelium not growing being killed off.
Symptoms: No Growth/Stalling.