Fermenting Safely.
Lactic ferments have an excellent safety record — because acid arrives fast. The danger is a ferment that does not sour.
Properly made vegetable ferments, yogurt and sourdough are among the safest foods there are: the lactic bacteria make the food too acid for pathogens within a few days, and keep it so. The risks come when that does not happen fast enough. Too little salt, too warm or too cold a room, too few lactic bacteria (over-washed or old vegetables, chlorinated water), or air reaching the food can let spoilers or pathogens get ahead (XIV.3).
Know the signs. Good: a clean sour smell, bubbles, cloudy brine, a white powdery film on the surface (kahm yeast — skim it), slight softening of old ferments. Bad: fuzzy mould in blue, green, black, pink or orange; slimy, mushy vegetables; a putrid or rotten-egg smell; a ferment that is still not sour after a week at room temperature. Then discard the whole jar — moulds spread invisible threads and some make toxins. And some things should not be home-fermented without tested methods: garlic or herbs in oil, low-acid foods in sealed jars, and fermented fish or meat. The workshop compares a good ferment with three bad ones.
Below: the pH of a vegetable ferment against days for a good set-up (2.25 % salt, 20 °C) and three faulty ones — no salt, too cold (8 °C) and too hot (32 °C) — and the hours each spends above pH 4.6 (microbe bench, teaching model).
- Recognise a healthy ferment.
- Recognise signs of failure.
- Know which failures cannot be rescued.
- Know which foods need tested methods.
Fast acid is safe acid
In this model a good set-up at 20 °C passes pH 4.6 in about 48 hours. At 8 °C it takes about 21 days — long enough for spoilers to get a foothold, which is why ferments are started at room temperature and moved to the cold once they are sour. At 32 °C it sours in 29 hours but the vegetables soften and off-flavours develop. Without salt it sours in 40 hours here, but the spoilers have had nothing to hold them back (XIV.3).
Rules that keep ferments safe. Weigh salt and vegetables; use clean jars and keep everything under the brine with a weight or a water-sealed lid; start at 18–22 °C; check with pH strips — below 4.6 within three or four days, ideally near 4 or below when finished; refrigerate when ready. Do not taste a ferment that smells rotten. Do not try to rescue a mouldy jar by scraping it. And treat preserved garlic or herbs in oil, home-canned ferments and fermented fish or meat as specialist work that needs tested methods (XIII.7, XIII.8).
Buy a pack of pH strips that read from 3 to 6. Test your next ferment every day and write down the readings. The day it passes 4.6 is the day it became safe.
Terms
- Kahm yeast
- A harmless white surface film on ferments; skim it.
- pH strips
- Paper strips that change colour with acidity, for checking ferments.
- Discard
- Throw away without tasting.
- Tested method
- A procedure whose safety has been checked by measurement.
Sources
- USDA Complete Guide to Home Canning (2015), Guide 6, "Preparing and canning fermented foods and pickled vegetables": sauerkraut with 3 tablespoons of canning salt per 5 lb of cabbage (about 2.25 % by weight); ferments in 3–4 weeks at 21–24 °C or 5–6 weeks at 15–21 °C; above about 24 °C it may soften, below about 15 °C it may not ferment.
- USDA National Institute of Food and Agriculture, Complete Guide to Home Canning, 2015 revision; National Center for Home Food Preservation.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.