pH, the lactic-acid arc, the gravity pair, the mordant bond — short, honest explainers with the math you'll actually use.
"2% brine" argues the whole internet, because two different numbers hide under those words: 2% of the water's weight (the standard for brined pickles) and 2% of the total weight of vegetable + water (the dry-salt kraut method). They land close but not identical — and neither is safe if you can't say which one a recipe meant. Lactic-acid bacteria tolerate 2–5% salt while spoilage organisms struggle at the bottom of that range; below 1.5%, pathogen risk climbs; above 6%, even Lactobacillus sulks and the ferment stalls. The app's rule is the site's rule: every percentage names its base.
A jar of brined vegetables is a succession story, not one species: first, enterobacteria bloom briefly while CO₂ builds and oxygen leaves (days 1–2, the cloudy brine is normal); then Lactobacillus takes over as pH falls — this is the main event, acidifying to roughly pH 3.5; finally acid-tolerant strains finish the job and the jar stabilizes for storage. Kahm yeast — the white film — is an aerobic squatter on the surface, not mold: skim it, keep everything submerged, and the batch continues. Fuzzy colored growth, on the other hand, means compost.
A hydrometer floats lower the more sugar the liquid holds. The two anchor readings — OG (original gravity, before yeast) and FG (final, after) — say how much sugar became alcohol: (OG − FG) × 131.25 ≈ ABV%. Mead at OG 1.120 finishing at 0.996 reads 15.4% — and the pair is also your sanity check: stuck batches show matching gravities days apart. Log both numbers every time; that's what the app's cellar timeline is.
Natural dye pigments are often water-soluble ghosts — they color once and rinse away. A mordant (alum, iron, tannin) is a metal salt that forms coordination bonds between fiber and pigment molecule, converting a stain into real colorfastness. The dosing is always a percentage of the fiber's weight — % OWF — so 8% alum on 100 g fiber is 8 g. Iron shifts colors toward gray and dark; pH shifts them sideways (cabbage goes pink in acid, green in base). The app's dye calculators do the OWF math and name the base every time.
CO₂ builds, bubbles form on the vegetable mass and climb: the visible proof of stage two — and the airlock burping its count.
Extraction to exhaustion in steps: the bath deepens, the fabric takes, the mordant locks it — colors at each step of a 60-minute simmer.
Sixty seconds, six questions, one honest recommendation.
Eight crafts, free log sheets, video from real makers, and an app that carries the calculators and recipes offline.