Contamination is a diagnosis, not bad luck
Green mold, wet spots, sour smells — most "failed" grows are telling you exactly what went wrong. Here's how a plant pathologist reads the signs, traces them back to the break in sterile technique, and fixes the cause instead of the symptom.
Every grower who's opened a bag to green dust or a sour, wet smell has had the same thought: bad luck. It wasn't. Contamination is not a random event that happens to otherwise-perfect technique — it's a symptom with a cause, and the cause is almost always identifiable if you're willing to look at it the way a pathologist looks at a sick plant instead of the way a grower looks at a ruined bag.
Read the symptoms like a pathologist
Different contaminants tell different stories. Fast-spreading green or blue-green dust is almost always Trichoderma — aggressive, airborne, and usually a sign that something was open to room air for too long during a transfer. A sour, fermented smell without visible mold points to bacterial contamination, usually from excess moisture or a substrate that wasn't fully sterilized. Black pin-sized dots are frequently Aspergillus or other airborne molds that settled during cooling. The point isn't to memorize a contaminant catalog — it's to notice that the type of contamination is data about the moment it got in.
Trace it back to the break
Sterile technique is a chain, and contamination means one link failed. Work backward through the chain in order: Was the substrate actually held at temperature and duration long enough to sterilize, or just long enough to look done? Was the workspace still-air or flowing air, and was it clean before you started? Was the transfer fast, or did the culture sit open while you fumbled with a lid? Did the incubation environment stay within a safe temperature range, or did a warm spell give competing organisms an edge? Most contamination traces to one of these four places, and once you know which one, you've found the actual problem — not just this bag's problem, but the one that will keep happening until you fix it.
Fix the cause, not the symptom
It's tempting to respond to contamination by being generally more careful next time. That rarely works, because "careful" isn't a technique — a specific, corrected step is. If your sterilization run was borderline, extend the hold time or check your pressure cooker's actual temperature rather than trusting the dial. If your transfers are slow, practice the motion empty-handed until it's fast enough that a culture is never open to room air for more than a few seconds. If your incubation space swings with the weather, add a thermometer and control for it directly. Treat each contamination event as a diagnosis rather than a disappointment, and your contamination rate becomes something you can actually drive down — because you're no longer troubleshooting luck.