Fermentation and enzymes in pizza dough

Short answer

During fermentation yeast feeds on sugars and produces carbon dioxide (the rise), ethanol and small amounts of flavour compounds, while bacteria add organic acids. At the same time enzymes from the flour break starch into sugars and slowly break down gluten — so a longer ferment changes flavour, browning and dough strength, not just volume.

What yeast is doing

Baker's yeast is a single-celled fungus. In dough it breaks down simple sugars and, with little oxygen available, produces mainly carbon dioxide and ethanol. The carbon dioxide is trapped by the gluten network and inflates the dough; the ethanol mostly evaporates during baking but contributes to aroma beforehand, and some of it reacts with acids to form aromatic esters.

Yeast is not alone. Flour and the environment carry lactic-acid bacteria, which produce lactic and acetic acids; in a sourdough they are a deliberate, major part of the culture, while in a commercial-yeast dough their contribution is smaller but grows with time. Those acids are a large part of why a long-fermented dough tastes more complex — explored in the sensory guide on long fermentation.

Enzymes: amylase and protease

Flour is not inert. It contains enzymes that become active once water is added. Amylases break starch — particularly starch granules damaged during milling — into smaller sugars such as maltose. That matters twice: it supplies food for the yeast over a long ferment, and it leaves free sugars in the dough that drive browning in the oven. Many bread flours have malted barley flour added partly to supply amylase.

Proteases break down proteins, including gluten. Over a short ferment their effect is minor; over several days, combined with accumulating acidity, they gradually make the dough more extensible and eventually weaker. A little of this is useful — a long-fermented dough is often easier to open — but taken too far the network loses its ability to hold gas.

Why cold fermentation behaves differently

Every one of these processes slows down in the fridge, but they do not all slow by the same amount. Cold sharply reduces yeast gas production, so the dough can sit for one to three days without over-rising, while enzyme activity and flavour development continue at a reduced pace. The practical effect is that a cold ferment buys time for flavour and extensibility to develop without the dough blowing out.

Browning can go either way. Amylase keeps releasing sugars, which supports colour, but yeast keeps consuming them. Within a typical 24–72 hour cold ferment with a modest yeast quantity, enough sugar usually remains; with too much yeast, too warm a fridge or a much longer ferment, the dough can bake noticeably paler.

Overfermentation

An overfermented dough has run past the point where its gluten can hold the gas being produced. Common signs are a slack, sticky ball that spreads rather than holding its shape, large bubbles that collapse when touched, a strong alcoholic or sour smell, and a crust that bakes pale and flat. The causes are usually too much yeast, too warm a temperature or simply too long.

What has happened is the sum of the mechanisms above: protease activity and acidity have weakened the gluten, yeast has exhausted much of the available sugar, and ethanol and acids have accumulated. Some overfermented doughs can still be baked, sometimes as a flatter pan pizza or focaccia-like bread, but they rarely recover the structure of a dough caught at the right time.

Common misconceptions

“Fermentation is just about making the dough rise.”

Rise is only one output. Fermentation also creates flavour compounds, changes gluten strength and alters how much sugar is left for browning.

“The fridge stops fermentation.”

It slows it substantially but does not stop it. Yeast, bacteria and enzymes all continue working, which is precisely why cold fermentation changes flavour.

“The longer the ferment, the better the pizza.”

Flavour generally deepens with time up to a point, but past the dough's window gluten weakens, browning can suffer and acidity can tip into sourness. The useful window depends on yeast quantity, temperature and flour.

What this page cannot tell you

This page describes mechanisms, not a fermentation schedule; the right timing for a dough depends on yeast quantity, temperature, flour and hydration, and fridges vary. It does not quantify how much sugar, acid or ethanol a given dough contains. PizzaHQ has not measured any of these processes.

Related

Evidence

• On Food and Cooking: The Science and Lore of the Kitchen (revised edition) — Scribner
• Wheat flour constituents: how they impact bread quality, and how to impact their functionality — Trends in Food Science & Technology (Elsevier), vol. 16, nos. 1–3, pp. 12–30
• The Science of Fermentation: The Secret to Good Pizza — Baking Steel
• Pizza Crust Lacks Browning? Causes & Fixes — PizzaBlab
• Modernist Pizza — The Cooking Lab