Yes — in low-acid, low-oxygen, low-salt conditions, it's rare but real, and it's exactly the failure mode our pH/salt/WPS thresholds exist to rule out. We treat these as hard floors, not folklore: if a recipe can't clear the threshold, we don't teach it or ship it as safe.

Temperature control, backslopping from a proven prior batch, pH tracking, and regular sensory analysis.

Yes — different failure modes need different controls. Lacto-fermentation leans on acidification: pH has to clear 4.6 to rule out botulism risk. Koji fermentation leans on water-phase salt (WPS) plus controlled humidity and temperature, to keep unwanted mould and bacteria out while Aspergillus oryzae does its work.

Water activity (aw) measures how much of the water in a product is actually available for microorganisms to use — not the same number as moisture content. Lowering it, through salt, sugar, or drying, is one of the core levers that makes a ferment shelf-stable and inhospitable to the pathogens you're worried about.

pH 4.6 (the critical botulism-risk threshold), correct salt ratio and temperature control, and always staying on the safe side around mould or pathogen risk — in our own production and in everything we teach.

Through pH, smell, texture, and visual checks against a known-good reference for that specific product — a ferment that's "funky but fine" and one that's actually spoiled look different in specific, learnable ways. This is part of what the consultancy curriculum's sensory-analysis and defect-identification module teaches directly.