A pizza made from dough that spent two days in the fridge usually tastes fuller and a little tangier than one made from dough mixed that morning. The popular explanation is that the cold switches the dough over to acetic acid. That’s partly right for sourdough and much less so for an ordinary yeasted dough. Here’s what the sources support.
What happens during a long ferment
Ken Forkish, in The Elements of Pizza (2016), calls time “the critical ingredient” that lets “a complex community of flora” build up in the dough: “yeast and bacteria as well as acids, esters, and other natural by-products of fermentation.” Of his 48- to 72-hour New York dough, he writes that the long, cold fermentation “lets flavors and mild acidity build and allows the proteins in the dough to break down just enough,” for a more delicate and more flavorful crust.
Modernist Pizza (2021), by Nathan Myhrvold and Francisco Migoya, describes the same process from the chemistry side:
- Yeast ferments sugars into carbon dioxide and ethanol.
- Lactic acid bacteria in the dough can break some of that ethanol down into acetic acid, and secrete enzymes that turn starch into sugars the yeast can eat.
- Time matters most: “The longer the period of fermentation, the more pronounced the yeast flavors become because the microbes have more time to produce aromatic compounds.”
The flour’s own enzymes work in parallel. Amylase makes sugar from starch, and protease snips gluten strands, which is part of why a long-fermented dough stretches more easily. How gluten works covers that side.
Lactic and acetic acid
Modernist Pizza describes two groups of lactic acid bacteria. Homofermentative bacteria produce lactic acid. Heterofermentative bacteria produce lactic acid, acetic acid and some carbon dioxide.
The two acids taste quite different. The book compares lactic acid’s mellow acidity to buttermilk or sour cream, and calls acetic acid, the main component of vinegar after water, “much more acidic and harsh.” It’s the combination, the authors say, that makes a levain’s flavor special.
What the cold actually changes
It slows everything down. Yeast, as Modernist Pizza puts it, “favors warmth over cold, as most living things do.” That’s the practical reason for refrigerating dough: it lets a dough wait a day or three without overfermenting, and the waiting is what builds flavor.
In sourdough, it can shift the balance of acids. Modernist Pizza says homofermentative bacteria enjoy warmer temperatures while heterofermentative bacteria prefer cold, and that some bakers split a levain’s ripening time between warm and cold. Temperature can change a sourdough culture’s acid balance, but the result depends on the culture and process. One 2021 laboratory study, by Johannes Pitsch and colleagues, kept rye and wheat sourdoughs whose cultures included acetic acid bacteria at 4°C (39°F) and 10°C (50°F) for 105 days, refreshing them weekly, and found different acid ratios at the two temperatures. That is a long-running starter experiment, not a pizza dough, and the paper states its ratio the opposite way round in different sections. These experiments don’t give a fixed acid ratio for a pizza dough refrigerated for a few days.
Cold doesn’t simply mean more sour. Modernist Pizza reports that a levain stored warmer reaches a lower pH and gives the baked crust a more noticeable acidity. The authors prefer a milder tang, so they keep their levain at 13°C (55°F), which they say extends its usable fermentation time and lets it develop the flavors of heterofermentative bacteria. That is their storage practice for a levain, not a rule for refrigerated pizza dough.
Yeasted dough is milder still. Modernist Pizza notes that commercial yeast gives dough a neutral flavor, while a levain imparts a sour one. A straight dough made with commercial yeast has no starter culture of bacteria, so its acidity stays mild, as Forkish describes. If you want a distinctly tangy crust, a sourdough pizza dough will do more than a longer stay in the fridge.
How long to cold-ferment
There’s no single peak. Published recipes give windows, and a dough’s flavor keeps changing within them:
| Recipe | Flour | Instant yeast | Room temperature, then fridge | Ready |
|---|---|---|---|---|
| Forkish, 24- to 48-Hour Pizza Dough | 500 g | 1.5 g (0.3%) | 2 hours bulk, then 16 to 48 hours in the fridge | Next evening (best) or the day after |
| Forkish, 48- to 72-Hour New York Pizza Dough | 500 g | 1.2 g (0.24%) | 2 hours bulk, then 48 to 72 hours in the fridge | Two days later (best) or the third day |
The Pizza Planner’s two cold schedules follow these recipe families: about 24 hours in the fridge at 0.3% instant yeast, or about 48 hours at 0.24%, each with a couple of hours at room temperature before and after.
Longer isn’t automatically better. Forkish warns that too much time leaves a dough that “expands too much, loses its integrity, and gets too full of hot air,” and Modernist Pizza notes that long fermentations can use up so much sugar that the crust bakes to a dull color. Go by the dough’s look and feel at the end of its window, not just the clock.
If you’re making dough today
A same-day dough can still taste good if it has time. Forkish’s Saturday Pizza Dough uses just 0.3 g of instant yeast for 500 g of flour and needs at least 8 hours from mixing to pizza at room temperature. He offers a quicker same-day dough for when you start late, but says that “the best doughs take a little more time.” The Planner’s same-day schedule follows the Saturday dough. If you can start the night before, a preferment such as Forkish’s biga builds flavor ahead of the final mix.
Frequently Asked Questions
- Does cold fermentation make pizza dough more sour?
- Not usually. In sourdough, Modernist Pizza says heterofermentative bacteria, which make acetic as well as lactic acid, prefer cold, but how a culture's acids actually balance depends on the culture and the process. The same book reports that a levain stored warmer reaches a lower pH. In a dough made with commercial yeast, the acidity that builds in the fridge is mild; Forkish calls it 'mild acidity.'
- What do lactic acid and acetic acid taste like?
- Modernist Pizza compares lactic acid's mellow acidity to buttermilk or sour cream, and calls acetic acid, the main acid in vinegar, much more acidic and harsh. A good sourdough flavor comes from the combination.
- How long should I cold-ferment pizza dough?
- Follow your recipe's window. Forkish's 24- to 48-Hour dough is best the next evening, and his New York dough is best after two days and still good on the third. The Pizza Planner plans about 24 or 48 hours in the fridge. Past the window, dough can lose its structure and use up the sugar that browns the crust.
- Is a long cold ferment the same as sourdough?
- No. A cold-fermented dough made with commercial yeast gains flavor and mild acidity from time. Sourdough is leavened by a culture of wild yeast and lactic acid bacteria, which gives it a distinctly sour flavor.
Sources
- Ken Forkish, The Elements of Pizza (2016): chapter 3 (time as an ingredient; mature and overfermented dough) and chapter 6 (the introduction to the dough recipes; Saturday Pizza Dough, 24- to 48-Hour Pizza Dough, 48- to 72-Hour Biga Pizza Dough and 48- to 72-Hour New York Pizza Dough).
- Nathan Myhrvold and Francisco Migoya, Modernist Pizza (2021), volume 1, printed pages 275 (flour enzymes), 292–293 (yeast fermentation, acetic acid from ethanol, the flavor of commercial yeast), 302 (lactic acid bacteria, the two acids and temperature), 304–305 (levain storage temperature and acidity) and 315 (sugar depletion in long fermentations).
- Johannes Pitsch and colleagues, “FODMAP Fingerprinting of Bakery Products and Sourdoughs: Quantitative Assessment and Content Reduction through Fermentation,” Foods 10, no. 4 (2021): 894, sections 2 and 3.4 and Figure 2 (rye and wheat sourdoughs fermented for 105 days at 4°C and 10°C; organic acid ratios).