April blue oyster bag run — 14% contam, three lessons

21 bags inoculated 2026-03-15. Substrate: 80% supplemented hardwood pellets, 20% soy hull, hydrated to ~62% moisture. Spawn: 5% by hydrated weight. Bagged in 5-lb autoclave bags with 0.5-micron filter patches.

Colonization was clean for the first 9 days. By day 12, three bags showed the green-spot signature of Trichoderma — all three on the same shelf, all three in the bottom row. The other 18 colonized fully by day 16 and were moved to fruiting.

Total fresh harvest across both flushes from the 18 healthy bags: 24.7 lb. That's an average BE of ~67%, dead center of the published range for Pleurotus ostreatus on supplemented hardwood. Nothing surprising about the yield; the contamination is what I want to write about.

All three contaminated bags were in the bottom row of the same shelf. The shelf above them held my pre-pasteurization wet-substrate bin for the day. I think substrate fines fell from the bin onto the filter patches of the bottom bags during a brief period when the bin lid wasn't fully seated.

This is exactly the kind of error that shows up only after the fact. The bin-lid was on; it just wasn't seated. A 1mm gap, an hour of foot traffic, and three bags eat trichoderma spores through their filter patches.

Going forward: filter patches face the wall on the bottom shelf, not the aisle. Cost me nothing. Two-second change to the workflow that would have saved 14% of the run.

1. Filter orientation rule — bottom-shelf bags always have filter patches facing the wall, not aisle traffic.
2. Lid integrity check — every wet-substrate bin gets a "lid clicked" verbal callout before I leave the room. This sounds dumb. It is dumb. It also catches the 1% case.
3. Spore swab the shelves monthly — I should already be doing this. I'm not. Adding it.

The 18 healthy bags fruited beautifully — first flush at day 21, second at day 38, with a 9-day rest between. Going to upsize to 30 bags for May and see if the workflow tweaks hold.