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Q: Do you have to test the pH of fermented products?

A: Yes. To produce a safe product, the pH fermentation brine must steadily drop to a safe pH of 4.6 or below to prevent C. botulinum growth. After reaching a safe pH, secondary spoilage may occur, which breaks down lactic acid resulting in a rising pH above 4.6, thus putting the product at risk for C. botulinum. Monitoring the pH from beginning to end of the vegetable fermentation process is critical to validate a safe product.

Monitor product pH during fermentation:

  • Daily, monitor and take pH readings with a calibrated pH meter from 2-3 samples from different areas of the brine and from each fermentation container. 
  • Kimchi ferments quicker than pickles or sauerkraut so test pH every 12 h for 2 days until pH < 4.6 at room temperature (68-72 degrees) or every day for 4 days until pH < 4.6 for fermentation under refrigeration (< 40°F).
  • Record date, time and pH readings to document continued decline in pH to < 4.6. Vegetable ferments usually reach a pH < 4.6 within a week. Lower temperatures take longer to reach a safe pH. 
  • Discard vegetable ferments that do not reach a pH of < 4.6 as incomplete, lightly fermented or half-sours pose a food safety risk.
  • Once a safe pH of < 4.6 is reached, continue to take weekly pH readings to verify the pH is not rising during the timeframe needed for a fully flavorful fermented product. Spoilage and rising pH is more common in no salt or low-salt ferments and at temperatures above 75°F. Discard vegetable ferments that rise in pH. Most products develop full flavor temperatures between 68°F and 75°F in 3 to 4 weeks and at 60°F to 65°F in 5 to 6 weeks to develop full flavor. 
  • Before putting into a container, confirm a final pH of ≤4.6.

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