A website from UGA Cooperative Extension

Published by UGA Extension Food Science and Technology 

Whether measuring the pH of a new food product for classification or as part of a routine test for quality or safety, it is important to understand the principles behind pH measurement and ensure testing is performed properly.

What is pH

“pH” is an acronym derived from the Latin term potentia hydrogenii, meaning the “power of hydrogen”. It measures the hydrogen ion (H+) concentration in a solution. The pH scale ranges from 0-14, with 1 being the most acidic and 14 being the most basic. Acids ionize in water, producing higher concentrations of H+. pH is measured on a reverse logarithmic scale (see equation below), so the higher the concentration of hydrogen ions, the lower the pH is.

pH = -log10[H+]

Why pH is Important in Food

pH has important impacts on the quality and safety of foods. In terms of quality, pH can affect color hue, flavor, consistency, and shelf life. In terms of safety, foods are classified based on their acidification and then processed accordingly to ensure they do not pose a food safety risk. According to the Code of Federal Regulations (21 C.F.R. § 114.3), foods can be defined based on their pH as follows:

  • Acid foods have a natural pH of 4.6 or below
  • Acidified foods are low acid foods with a water activity greater than 0.85 to which acid(s) are added to obtain a finished equilibrium pH of 4.6 or below
  • Low-acid foods are foods, other than alcoholic beverages, with a finished equilibrium pH greater than 4.6 and a water activity greater than 0.85

pH is especially important in canned foods. The threshold pH value of 4.6 for defining high versus low acid foods is based on the growth parameters of the bacteria Clostridium botulinum. C. botulinum produces spores that can proliferate and produce a lethal toxin, which causes botulism. Botulism is a major concern with canned foods because C. botulinum spores grow in environments with little to no oxygen. However, Clostridium botulinum spores will not grow at a pH less than 4.6, thus the threshold pH value of 4.6 for defining food acidification. Generally, it is advised for businesses producing canned foods to obtain a pH of 4.2 or below to guarantee the safety of their products. Products with a pH between 4.2 and 4.6 are susceptible to growth of acid-tolerant spore formers that can cause undesirable food spoilage.

Producers of both acidified canned foods and low-acid canned foods must register their formula and processing procedures with the FDA by filing form 2541e. Prior to this, producers must work with a Process Authority to validate their process. This is referred to as their scheduled process. UGA Food Science Extension offers Process Approval letters as one of our services. If interested, please reach out to ufs@uga.edu or visit our website for more information.

Proper pH Measurement

When measuring the pH of a food sample, it is important to follow proper procedures to accurately determine the pH of the food product. Common and potentially dangerous mistakes include not properly calibrating your pH meter, measuring the pH while the product is still hot during canning, and not correctly preparing the food sample before pH measurement.

  1. Calibrate your pH meter prior to taking a pH measurement. pH meters should be standardized with commercially prepared standard 4.0 pH buffer (see 21 C.F.R. § 114.90(a)(4) for more information on calibration protocols). Care should be taken to ensure the pH probe is stored in a buffer solution or a solution specified by the pH meter manufacturer to ensure the probe does not dry out. Additionally, be sure to rinse the probe with water and gently blot the electrode with soft tissue prior to use and between measurements (wiping or rubbing , instead of blotting, can lead to static charge building up).
  2. Ensure the temperature of the food is at 25C. At higher temperatures, ion dissociation increases (forming H+), resulting in a drop in pH. As a result, if you measure the pH of your food sample before letting it cool to 25C, the pH reading will be lower than that of the actual equilibrium pH of the food.
  3. Blend samples that contain solids. Before measuring the pH of a sample that contains a mixture of liquids and solids (e.g. peppers in vinegar solution), blend the contents to a uniform paste, adjust the temperature to 25C, and then measure the pH. It is important that the ratio of solids to liquids in the measured sample is representative of the solid to liquid ratio of the food product that you are evaluating. If there is not enough water to make a paste, add 10-20 mL of distilled water per 100 grams of product and blend. For more information on sample preparation, please see 21 C.F.R. § 114.90(a)(6).

We hope this blog post helps you better understand what pH is, why it is important in canned foods, and proper pH measurement techniques! If you have any questions, please reach out to us at efs@uga.edu or call 706-542-2574.