Tell us the recipe context and the measured finished pH (24–48 hours after bottling and at thermal equilibrium).
Measure 24–48 hours after bottling, at room temperature, with a calibrated pH meter (not litmus paper — litmus is too imprecise at this range). Calibrate the meter against pH 4.01 and 7.00 buffers immediately before measuring.
Clostridium botulinum is an anaerobic bacterium whose spores can survive boiling temperatures. In sealed, anaerobic packaging (a bottle, a jar), the spores can germinate and produce botulinum toxin — a lethal neurotoxin — if the food's pH is greater than 4.6. At pH ≤ 4.6 the spores cannot germinate, which is why FDA draws the regulatory line at exactly that value. The 0.4 unit margin of safety (target pH < 4.2) is industry practice on top of the legal threshold to handle batch and measurement variation.
Enter your measured equilibrium pH on the left to get a safety check.
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