pH meters and strips
pH is the one number that tells you whether a ferment has got where it needs to be. Strips or a meter, which to choose and how to measure well with each.
6 min read Getting good Reviewed October 26, 2026 28 facts, each with its source
Why measure pH
What decides whether a vegetable ferment has worked is its pH dropping to 4.6 or lower1. Above that, in a ferment that's spoiling, the spores of the botulism bacterium can germinate2. Its toxin can't be seen, smelled or tasted3. Smell, texture and taste say a lot about quality, but they are not a reliable indicator of safety4.
That's why pH is the number that rules. A ferment is ready when it has reached 4.6 or lower and the bubbling has stopped5.
The numbers: 4.6 and 4.2
| pH | What it means |
|---|---|
| Above 4.6 | Not yet. Let it keep fermenting and measure again |
| 4.6 or lower | It has passed the limit the guides set |
| 4.2 or lower | The point Fervida recommends before the fridge |
The 4.2 is a house rule for sauerkraut and brine pickles: it leaves a margin below the limit. It matches the figure below which BCCDC lets fresh sauerkraut be packed6 and kimchi's optimum pH7.
pH strips
They're cheap and quick, and for following a ferment at home they usually do the job. Choose narrow-range strips that read from 3.0 to 5.58, or from 0 to 6 in steps of 0.59. Strips that run from 1 to 14 have steps too coarse to tell 4.2 from 4.6. Use them the way the manufacturer says10.
They have three limits: they can't be calibrated, the color of the ferment can confuse the reading, and they can be off by as much as one pH unit11. Red cabbage, beets or kimchi will stain the strip. Below 4.0, pH paper is acceptable even for people who sell preserved foods12, but between 4.0 and 4.6 a strip doesn't give you the certainty of a meter. If the strip reads right at the limit, wait a few days and measure again, or use a meter.
pH meter
A pH meter is the best way to measure pH13, and it doesn't have to cost much: there are reliable, accurate meters for under $10014. When choosing one, look at two things:
- Accuracy. Most are accurate to about 0.1 pH unit15. Look for one that shows at least one decimal place.
- Temperature. pH changes with it, and an automatic temperature compensator corrects the reading16.
Always use and calibrate it the way its manufacturer says17.
Calibrating it
A pH meter is calibrated with buffer solutions of known pH. For ferments, the usual is a two-point calibration, with pH 4 and pH 7 buffers18:
- Turn it on and put the electrode in the pH 4 buffer. Calibrate.
- Rinse the electrode with distilled water19.
- Put it in the pH 7 buffer and calibrate.
- Rinse again.
Calibrate and measure at room temperature, between 20 and 30 °C (68 and 86 °F), ideally 25 °C (77 °F)20. If you're measuring a ferment straight from the fridge, let the sample warm up first. When you're done, clean and store the meter as the manufacturer says21.
How to measure a ferment
The pH of the brine and the pH of the vegetables don't always match22. The reading that counts is both together, blended in the same proportion as in the jar23:
- With a clean spoon, take a little of the vegetables and the brine into a glass.
- Blend it. If it's very solid, add a little distilled water to make a slurry24.
- Measure, rinse the electrode and repeat twice more. Average the three and write it down25.
- Throw the sample away: don't put it back in the jar.
Writing down every reading shows you what a normal ferment looks like in your kitchen26. In Fervida's batch diary you can log the pH of each jar and, with a meter, see its curve.
When to measure
Where every number comes from
Every number in the text leads to its figure: the exact sentence from the official guide it comes from, in its own language.
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1
The control point of a vegetable ferment is pH dropping to 4.6 or lower
“The critical control point in vegetable fermentation is a pH drop to 4.6 or lower.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.1: Fermented Vegetables (August 2024, updated December 2024) · read on October 25, 2026
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2
Above 4.6, botulism spores can germinate
“C. botulinum spores may germinate in fermented foods when pH rises above 4.6 during spoilage.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.1: Fermented Vegetables (August 2024, updated December 2024) · read on October 25, 2026
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3
You can't see, smell or taste the botulism toxin
“You cannot see, smell, or taste the toxin that causes botulism.”
Centers for Disease Control and Prevention (CDC) · Botulism Prevention · read on October 25, 2026
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4
Smell, texture and taste are not a reliable indicator of safety
“Sensory analysis, referring to the evaluation of smell, texture and taste of a food, may also be recommended when assessing quality of the food, but is not a reliable indicator of food safety.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 2: Starter cultures and fermented food standards (August 2024, updated December 2024) · read on October 25, 2026
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5
It's ready at pH 4.6 or lower with no more bubbling
“When a pH of 4.60 or lower is reached and bubbling has stopped, the ferment is ready.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026
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6
Fresh sauerkraut is packed once pH is below 4.2
“Fresh sauerkraut can be packaged when pH is below 4.2”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.2: Sauerkraut (2024) · read on October 26, 2026
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7
Kimchi's optimum pH is 4.2
“results in an optimum kimchi pH of 4.2.”
Colorado State University Extension · Understanding and Making Kimchi (2025) · read on October 20, 2026
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8
pH strips that read from 3.0 to 5.5
“To verify pH, use a pH test strip that can test a range of 3.0-5.5 pH.”
Colorado State University Extension · Understanding and Making Kimchi (2025) · read on October 20, 2026
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9
Or from 0 to 6, in steps of 0.5
“Using a test strip with a test range of 0-6, with increments of 0.5 is recommended.”
Colorado State University Extension · Understanding and Making Kimchi (2025) · read on October 20, 2026
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10
Follow the manufacturer's instructions
“Follow the manufacture's instructions for testing.”
Colorado State University Extension · Understanding and Making Kimchi (2025) · read on October 20, 2026
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11
Strips can't be calibrated, food color confuses them and they can be off by 1 point
“PH strips are not acceptable because they cannot be calibrated, the colour of the food being tested can change or confuse reading the pH results on the strip, and strips have a poor detection limit with variations of ± 1 pH unit.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 2: Starter cultures and fermented food standards (August 2024, updated December 2024) · read on October 25, 2026
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12
Below 4.0, pH paper is acceptable
“If the pH is below 4.0, other methods can be used such as pH paper or a pH meter with one decimal place.”
Cornell Food Venture Center (Cornell AgriTech) · Acid & Acidified Foods · read on October 25, 2026
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13
A pH meter is the best method
“A pH meter is the best method to measure pH and it is recommended for all products and values.”
Cornell Food Venture Center (Cornell AgriTech) · Acid & Acidified Foods · read on October 25, 2026
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14
There are reliable pH meters for under $100
“There are inexpensive (less than $100) pH meters that are reliable and accurate.”
Virginia Cooperative Extension (Virginia Tech) · What do I need to know to sell KOMBUCHA at the farmers market? (FST-297, last reviewed November 2025) · read on October 20, 2026
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15
Most pH meters are accurate to about 0.1 pH
“The accuracy of most pH meters is stated to be approximately 0.1 pH unit”
U.S. Food and Drug Administration, Code of Federal Regulations (eCFR) · 21 CFR 114.90 Methodology: determining pH · read on October 26, 2026
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16
Without compensation, temperature shifts the reading; an automatic compensator corrects it
“Any temperature determinations made without meter compensation may affect pH values. An automatic temperature compensator may be used.”
U.S. Food and Drug Administration, Code of Federal Regulations (eCFR) · 21 CFR 114.90 Methodology: determining pH · read on October 26, 2026
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17
Follow the manufacturer's instructions for use and calibration
“For accurate measurement using a pH meter, it is important to follow the pH meter manufacturer instructions for use and calibration.”
Virginia Cooperative Extension (Virginia Tech) · What do I need to know to sell KOMBUCHA at the farmers market? (FST-297, last reviewed November 2025) · read on October 20, 2026
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18
Two-point calibration, with pH 4 and pH 7 buffers
“we are using a meter that performs a two-point calibration. This requires the use of pH 4 and pH 7 buffer solutions.”
Oregon State University Extension Service · pH meter calibrating and testing for pickled food products (video transcript, 2022) · read on October 26, 2026
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19
Rinse the electrode with distilled water in between
“Rinse the electrode with distilled water and repeat the process with the 7.0 buffer solution.”
Oregon State University Extension Service · pH meter calibrating and testing for pickled food products (video transcript, 2022) · read on October 26, 2026
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20
Measure between 20 and 30 °C (68–86 °F), ideally 25 °C (77 °F)
“Tests should be made at a temperature between 20° and 30 °C, the optimum being 25 °C.”
U.S. Food and Drug Administration, Code of Federal Regulations (eCFR) · 21 CFR 114.90 Methodology: determining pH · read on October 26, 2026
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21
Clean and store it as the manufacturer says
“After completing testing, follow the instructions included with your meter to properly clean and store it.”
Oregon State University Extension Service · pH meter calibrating and testing for pickled food products (video transcript, 2022) · read on October 26, 2026
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22
Liquid and solids can differ in acidity
“Some food products may consist of a mixture of liquid and solid components that differ in acidity.”
U.S. Food and Drug Administration, Code of Federal Regulations (eCFR) · 21 CFR 114.90 Methodology: determining pH · read on October 26, 2026
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23
Solids and liquid blended together, in their proportion
“Mix aliquots of solid and liquid fractions in the same ratio as found in the original container and blend to a uniform consistency.”
U.S. Food and Drug Administration, Code of Federal Regulations (eCFR) · 21 CFR 114.90 Methodology: determining pH · read on October 26, 2026
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24
For solids, a slurry with a little distilled water
“Add a little bit of distilled water to the solid beans to create a slurry.”
Oregon State University Extension Service · pH meter calibrating and testing for pickled food products (video transcript, 2022) · read on October 26, 2026
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25
Measure three times and average
“repeat the process two more times. Average the pH readings and record that figure in the pH testing log.”
Oregon State University Extension Service · pH meter calibrating and testing for pickled food products (video transcript, 2022) · read on October 26, 2026
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26
Keeping records shows you what a normal ferment looks like
“Operators are recommended to keep records of pH results. This will provide objective information for what a normal, healthy fermentation process looks like.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 2: Starter cultures and fermented food standards (August 2024, updated December 2024) · read on October 25, 2026
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27
Kimchi, daily until it reaches 4.6
“testing it daily until a pH of 4.6 or below is reached.”
Colorado State University Extension · Understanding and Making Kimchi (2025) · read on October 20, 2026
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28
If bubbling has stopped but it's still above 4.6, check every 1 to 2 days
“If bubbling has stopped but the pH is still above 4.60, continue to ferment and check the pH every 1 to 2 days.”
University of Minnesota Extension · Preserving food at home: Fermentation (reviewed 2026) · read on October 25, 2026