Bacterial Wet Spot
Contamination by bacteria rather than mould, shown by slimy patches and a sour smell. It follows over-wet or under-sterilised substrate.
What it is
Bacterial wet spot, also called bacterial blotch, is contamination by bacteria rather than mould. It usually follows substrate that was too wet or not fully sterilised.
How to spot it
Look for slimy, wet, grey or yellowish patches and a sour or rotten smell. In grain it can show as a dull, wet zone that never colonises. The sour smell is the clearest sign.
Prevention
Get your moisture right, around 60 to 70% for bulk substrate and 45 to 55% for grain, and sterilise or pasteurise thoroughly. Let jars cool fully before inoculating and avoid trapping excess water in the container.
What to do
There is no practical cure once bacteria take over, because they outcompete the mycelium. Discard the affected material and review your moisture and sterilising steps before the next batch.