pH

pH is a number for how acidic or basic a watery solution is. Minnesota Department of Agriculture, teaching FDA acidified-food rules: the scale runs 0 to 14; at room temperature, below 7 is acidic, 7 is neutral, above 7 is basic; the lower the value, the more acidic the food ¹. NCHFP uses the same idea in canning language: “pH” measures acidity; the lower the value, the more acid the food ².

Acidity is the food-acid page — lactic, acetic, tartaric, citric, sour taste, gel, wine. pH is the scale and the meter. Do not read them as twins.

Why it matters #

Taste is not a pH meter. A lemon and a properly acidified pickle can both taste sharp; only a measurement tells you where you sit on the 4.6 line that U.S. canning law cares about. Minnesota’s example: vinegar typically has a pH of 2.5 ¹. That is their typical figure, not a table of every condiment.

The scale, then the legal line #

You do not need a buffer table to cook. A splash more vinegar is not a calculated canning process. Calibration follows the meter manufacturer’s instructions.

21 CFR 114.3, for acidified foods:

• Acid foods — natural pH of 4.6 or below.
• Low-acid foods — finished equilibrium pH greater than 4.6 and water activity (aw) greater than 0.85 (alcoholic beverages excepted; tomatoes and tomato products with finished equilibrium pH less than 4.7 are not classed as low-acid).
• Acidified foods — low-acid foods to which acid or acid foods are added, with aw greater than 0.85 and finished equilibrium pH of 4.6 or below.
• Water activity — free moisture as the ratio of the food’s water vapor pressure to that of pure water at the same temperature ³.

NCHFP/USDA home canning: low-acid foods (pH higher than 4.6) include red meats, seafood, poultry, milk, and fresh vegetables except most tomatoes; acid foods (pH 4.6 or lower) include fruits, pickles, sauerkraut, jams, jellies, marmalades, and fruit butters. Some tomatoes and figs sit slightly above 4.6 and must be acidified if they are to be treated as acid foods ². Process choice — boiling-water versus pressure — lives on Canning and Food safety, not as a scare essay here.

Minnesota: equilibrium pH is when solids and liquid in the jar read the same; that can take hours or days ¹. A surface dip of pH paper on a chunky salsa is not equilibrium. Water activity is the other number in the legal definition; a dry food can sit above pH 4.6 and still not be that canned-food problem.

In the kitchen, when it is not a jar #

Fermentation lowers pH as acids accumulate — Fermentation, Pickling. Cheese making watches pH so casein will set — Coagulation. Jam needs acid in a workable window for pectin; that is still the acidity/jam pages, not a home-invented pH target. If you do not have a calibrated meter and a tested process, you are tasting and following a formula, not running a lab.

What to observe #

Failure modes #

• Confusing sour with safe. Quality. The jar still needs the researched process.
• Reading pH 4.6 as a flavor target. It is a process split.
• Ignoring water activity. The CFR definition uses both numbers ³.

Action: taste for cooking; measure when a tested process or a regulation says to. Then go back to Acidity for what those acids are doing in bread, cheese, wine, and jam.