HOW TO CHECK pH FOR CANNING

We can monitor the pH of food that we preserve – some can be tested by using paper pH strips (known as litmus paper) or, for greater accuracy, a digital pH meter (which is what we recommend). pH testing is not essential for home canners, as reputable preserving recipes for water bath canning and pressure canning will have used scientific methods to check this for you. It is, however, a requirement for commercial food production and interesting to understand why some recipes cannot be adjusted (because the pH may be affected, thus interfering with food safety).

 

The pH of home canned food is always tested after equilibrium (24 hours after processing in a water bath canner) because the pH before canning (or directly after canning) are all different to the equilibrium pH reading (which is the most accurate reading). For pickled vegetables or fruit, equilibrium is about 3 weeks.

Paper pH test strips are used to measure pH of food if it is pH 4.0 or less. When the paper is dipped into the food solution, the paper colour will change, indicating the pH of the food. Litmus paper are cost effective but can be inaccurate (and possibly difficult to read and understand the results).

 

A pH meter is essential if you are regularly monitoring, testing and recording the pH values of canned food to ensure it is safe – i.e. for commercial food production. pH meters must be used if the food is equal to or higher than 4.0. A pH meter has a glass electrode that is immersed in a food solution to measure the amount of hydrogen-ion (acid) in the food. pH meters require calibration with pH 4.0 and pH 7.0 buffers before testing food. Before calibration, remove the cap from the pH probe and rinse with distilled water. Dip the probe into a small container of 7.0 buffer. Record pH reading (should be 6.9-7.1). Rinse probe with distilled water and then dip the probe into a small container of 4.0 buffer. Record pH reading (should be 3.9-4.1). If the pH meter reading/s are outside the ranges above, you will need to calibrate the pH meter as per the pH meter manufacturing instructions, then repeat the calibration check. Calibrate your pH meter each day before testing the pH of food.

 

Looking at buying a pH meter? These are the main four considerations:

o  Accuracy – listed as range of +0.XX pH units i.e. accuracy of the results is 0.XX pH units above (or below) the actual pH of the food. Accuracy of +0.01 in a pH meter is very good, +0.02 is good, … +0.10 is not accurate enough.

Example: accuracy of pH meter is +0.2, meter reads 4.2, actual pH of the food being tested could be 4.0-4.4 (especially if your food needs to be under 4.6 for safety/legally if selling)

o  Calibration – coloured liquids with a known pH are called standards. These standards are used to calibrate the pH meter by testing the pH of the standard with the pH meter. 2-point calibration is the minimum recommended in a pH meter. You will also need pH 4.0 and pH 7.0 buffers (standards). More expensive pH meters are easier to adjust (less fiddling) for calibrating. Store buffer solutions in their containers, sealed airtight between uses and replace every two years (TIP: write date opened on the bottles).

o  Electrode – the part of the pH meter immersed in a food solution is called the electrode. When looking at buying a pH meter also look at the cost of replacing electrodes (some have special tips to reduce clogging). Cheaper pH meters may not have replacement electrodes available and will require buying a whole new pH meter instead of just replacing the electrode.

o  Temperature – more expensive pH meters will adjust readings if samples are too warm or too cold. For canned food readings, these are done at room temperature (after equilibrium i.e. 24hrs after canning).

 

HOW TO CHECK THE pH OF HOME CANNED FOOD

1.  Open room temperature jar of canned food after 24 hours (minimum) of processing in a water bath canner. For pickled vegetables or fruit, equilibrium is about 3 weeks.

2.  Strain jar contents to remove liquid (i.e. brine/syrup). The pH of solid food is tested, to ensure enough vinegar in pickles for example reached the innermost part of the vegetables).

3.  Place solid food into a blender and blend until smooth, adding distilled water to make it a thin consistency (like a smoothie). Distilled water makes it easier to test the pH and does not affect the pH reading. Runny sauces, like barbecue sauce, usually do not need water added for testing.

4.  Test pH of food solution with pH meter OR paper pH test strips.

5.  Record results in your logbook (example below).

 

Food Name	Batch Number		Equilibrium		Check #1		Check #2
	#	Date	Date	pH	Date	pH	Date	pH

 

Link: pH meters on Amazon AU https://amzn.to/3DTCMFy

Link: paper pH test strips on Amazon AU https://amzn.to/3jLvhts

 

Author: Megan Radaich           

Image Credit: Megan Radaich            

Publication: www.foodpreserving.org