07 May 2025 6 min read pH

On pH and sourdough breads

(you don't really need a pH meter, but you might want one)

[This is yet another section from the book that might need to get axed, so here it goes for now.]

pH is one of those metrics which many bakers never think about, because measuring the pH of doughs and levains requires specialized equipment. But nowadays reasonably-inexpensive bread dough-specific pH meters are available, which makes peeking under the hood pH-wise easier than it used to be. While monitoring dough and levain pH is not essential for success in bread baking, having a pH meter gives you yet another tool to understand why things work well (and why things go wrong). I’m not suggesting at all that you need a pH meter, but it’s worth understanding pH just the same, and, like me, you might find one useful, at least for a while.

pH refers to the “potential of hydrogen” of a water-based solution, or its acidity or basicity. Water molecules (H₂O) constantly shuffle between two forms, one where both hydrogens are directly attached to the oxygen—H-O-H—and another where one detaches to form a hydrogen ion (H⁺, aka a “proton”) and a hydroxide anion (^-OH). When the number of H⁺ and ^-OH ions are balanced, the solution is neutral, with a pH of 7; distilled water has a pH of 7.

When there are more ^-OH ions than H⁺ ions, the solution is basic, with a pH greater than 7, up to a maximum of 14; more H⁺ than ^-OH ions, the solution is acidic, with a pH of less than 7 (down to a “maximum” of 0).

The pH scale is logarithmic, not linear, which means that each shift of 1 unit in either direction represents a tenfold shift in absolute numbers. In other words, pH 4 is 10 times more acidic than pH 5. Similarly, pH 10 is 100 times—10 x 10—more basic as pH 8. This is important to keep in mind when tracking the movement of pH—a seemingly small shift in pH is much larger than the numbers suggest.

Here are some common aqueous solutions and their pHs, along with that of some important stages for sourdoughs:

Aside from eggs, baking soda, and lye, most aqueous kitchen ingredients (even a mixture of flour and water) are acidic. And since the byproducts of fermentation include lactic and acetic acids, all of the stages of bread fermentation are acidic.

Sourdough starters and pH

Normally bakers think about the phases of sourdough starter fermentation in terms of expansion in volume. As always, everything depends upon multiple factors—flour type (refined vs. whole-grain), hydration (stiff or liquid), temperatures, inoculation rate, etc.—but most starters follow a predictable course, especially when these variables are held constant from one batch to the next.

While an experienced baker can simply use their eyes (and nose) to track the course of sourdough levain and dough fermentations, its pH also follows a predictable curve:

When first mixed, a levain will be slightly acidic, with a pH around 5.5.
A young levain will have a pH between 4.2 to 4.0.
A mature levain will sit between pH 3.9 and 3.7.
And an overproofed levain will have a pH below 3.7.

Sourdough doughs and pH

Like starters, freshly-mixed bread doughs begin at around pH 5.5, and are considered mature—meaning the bulk fermentation is complete—somewhere between pH 4.7 and 4.0. Doughs that drop below pH 4.0 during the bulk are likely to overproof after shaping, since they’ll continue to acidify during the final proof. Bakers don’t generally take pH readings of shaped loaves, but as with levains, once they dip below pH 3.7 they are at risk of collapse.

pH and rye sourdoughs

One place some bakers routinely use pH meters is when making 100%-rye flour breads. Rye flour is especially active enzymatically, and enzymes are very sensitive to pH.

Amylase, the enzyme responsible for breaking down starches, is most active between pH 5.5 and 4.5. If amylase is not kept in check, it can cause the starches in the loaf to break down quickly, especially during baking, when the heat further amps up enzymatic activity, and the interior of the loaf can collapse, leaving a gummy crumb and a hollow beneath the top crust. (Runaway amylase activity in ryes is known as starch attack, and the hollow is called a flying roof.) This is why many rye bakers use a high percentage of sour (rye levain) in their doughs; that way the dough starts out acidic enough to limit amylase activity.

Meanwhile, pentosanase, which breaks down the pentosans that give rye breads structure, is most active between pH 4.0 and 3.5; when pentosanase activity is very high, the loaf can rapidly lose volume during the proof or in the oven. This leaves a narrow optimal pH window for sourdough ryes—4.5 to 4.0. While having a pH meter is not essential for rye baking, it can be a lifesaver here.

TTA, the buffering effect, and FQ

pH is an inexact measure of dough acidity, because it only accounts for H⁺ protons floating around freely. Like water, acids exist in two forms: lactic acid forms a lactate anion and H⁺, acetic acid, an acetate ion and H⁺. But sometimes those protons get masked by elements in the dough, rendering them invisible to pH meters, despite still having a potentially-negative effect on the resulting bread (and being detectable, flavor-wise).

This is called the buffering effect, and it is especially pronounced in doughs containing whole-grain or high-extraction flour. A far more accurate measure for acidity is total titratable acidity, or TTA, but measuring TTA requires specialized equipment and a time-consuming process that makes it impractical for most bakers to perform. Still, it is worth remembering that, in certain cases, pH as measured with a meter is only an approximation of the true acidity of a dough.

Neither pH nor TTA say anything about what sorts of acids are present in a dough. Protons are protons, no matter where they come from. The relative ratio of lactic and acetic acid in a dough is known as the fermentation quotient (FQ), but it’s not something a baker can easily determine.

Practical uses of pH meters in sourdoughs

Whether with a sourdough leaven or a dough, using a pH meter can help you better understand exactly at what stage of the process it is. I’ve found mine especially helpful in a few ways:

I occasionally move a levain to the fridge if I cannot use it right away. Because fridge temperatures slow down its expansion, it can look nearly the same later on as it did going in. Only by taking a pH reading can I confirm it hasn't overproofed.
Bakers usually mark the end of bulk fermentation—and the go-ahead to begin dividing and shaping—by tracking the expansion of the dough. It is generally better to shape before the dough is overly gassy and strong, which can leave it hard to do. But I know from experience that it’s not always easy to know when a dough is ready until it’s too late. Visualizing expansion is challenging when it’s modest (say 25-30% larger than its original volume), no matter what container you use to hold it. When I started tracking pH, I realized that my doughs commonly fell into the 4.7–4.0 pH window before I’d normally consider them ready. Using one helped me retrain my eyes to know exactly when to begin shaping.
Though I don't often use it during the final proof of loaves, I occasionally take it out just to be sure the loaf isn't at risk of overproofing, especially when I am trying to push the fermentation as far as possible.
And I used my pH meter often when learning to make 100%-rye sourdoughs over the last few years, though nowadays I can judge readiness or spot problems by eye.

Should you purchase a pH meter?

No—unless you really want one. I haven't tested more than a couple, both made by Hanna Instruments, and this is this one I have now:

If you are tempted to purchase one, keep in mind that pH meters are fussier to use and maintain than other devices like thermometers. The probe must be kept in a storage solution at all times to prevent the electrodes from drying out or corroding; most come with a little vial that also serves as a protective cap. And they need to be cleaned and calibrated regularly to ensure readings are accurate.

Do any of you already have and use pH meters? Are you curious to own one?

—Andrew