Fermenting

What is actually happening

Yeast eats the simple sugars in the flour and gives back carbon dioxide, alcohol and a long tail of aromatic compounds. Enzymes in the flour break starch down into more sugar as they go, which is why a dough that has fermented for two days browns faster than one mixed an hour ago: there is more sugar left on the surface when it hits the oven.

At the same time the gluten network is relaxing and reorganising. A well-fermented dough opens without fighting back. An underfermented one snaps back at you and tears in the middle, and no amount of stretching technique fixes it.

Two clocks run at once. The gas clock decides how puffy the dough is. The flavour clock is slower. Cold fermentation exists to let the second clock run long while holding the first one still.

Bulk versus ball

Bulk fermentation, puntata in Naples, is the rise while the dough is still one mass. It builds strength and does most of the flavour work.

The ball proof, appretto, is the rise after dividing. It is what makes a ball extensible enough to open into a disc.

Where you spend your time changes the result. A long bulk and a short ball proof gives a stronger, chewier crust. A short bulk with a long ball proof gives a softer, more extensible dough that opens easily and puffs hard, which is why Neapolitan schedules are weighted that way.

Cold fermentation, step by step

The workhorse method for New York, Detroit, al taglio and most things baked at home. The fridge slows yeast activity to roughly a quarter of room temperature, while the flour's enzymes keep working, so you get days of flavour development with only a modest rise.

• Mix and knead as usual, aiming for a finished dough temperature around 24C. Warmer than that and the dough will have run ahead before the fridge slows it down.
• Bulk at room temperature for 1-2 hours. This head start matters: yeast that goes straight into the cold takes hours to do anything, and dough that is chilled from the moment it is mixed often never gets going.
• Divide and ball now, not later. Balls chill through in about an hour; a five kilo mass takes most of the night, and the outside overferments while the middle is still warm.
• Oil the tops lightly, put them in a covered box or individual containers with room to expand, and refrigerate at 3-5C.
• Hold for 24 to 72 hours. Day one is a rise. Day two is where the flavour arrives. Day three is the best it gets for most doughs, and past four it starts breaking down into something slack and boozy.
• Take the balls out 2-3 hours before you bake, still covered. This is the step people skip and it is the one that ruins the pizza: cold dough is stiff, tears in the middle, and does not puff. It should feel slack and slightly domed before you open it.

How much yeast for a cold ferment

Less than you think, and it scales with the whole schedule rather than any single stage. As a rough guide with instant dry yeast: 0.5% for a same-day dough, 0.3% for 24 hours cold, 0.2% for 48 hours, 0.15% for 72 hours.

The calculator on the front page works this out properly from your actual stages and temperatures, including the warm bulk before the fridge and the warm-up after it, because those two warm hours contribute more activity than six hours in the cold.

If your dough is inflating in the fridge and pressing the lid off the box, you used too much. If it comes out flat and unchanged after two days, you used too little, or your fridge runs colder than you think. A cheap fridge thermometer settles that question permanently.

Room temperature, straight through

The Neapolitan way, and the fastest route to a dough that opens beautifully. Everything happens between 18 and 25C over 8 to 24 hours, with the yeast dose cut right down to stretch it.

It needs a stable temperature to be predictable, which is the catch. A kitchen that is 19C overnight and 26C by afternoon will not give the same result twice. A cheap styrofoam or plastic proofing box with a bowl of warm water buys a great deal of consistency for very little money.

The upside is texture. Dough that has never been chilled is softer and more extensible, and it puffs harder in a very hot oven.

Poolish

A loose preferment: equal weights of flour and water, a trace of yeast, left 12-16 hours until it domes and just begins to sink. It is ready at the moment the surface goes from tight to slightly wrinkled.

Poolish buys aromatic complexity and extensibility. It suits Neapolitan and contemporary high-hydration doughs, where you want a dough that opens like fabric.

Use 20-40% of the total flour in the poolish. Take that flour and water out of the final mix rather than adding it on top, which the calculator does for you.

Biga

The stiff Italian preferment: 45-50% hydration, barely mixed, left 16-18 hours somewhere cool, ideally 16-18C. It should look shaggy and torn, never smooth.

Where poolish softens, biga strengthens. It gives a drier, more open crumb and a nuttier flavour, and it is the traditional route for al taglio and for very high hydration doughs that need the extra backbone.

A biga run too warm turns sour and sharp. If your kitchen is hot, use less yeast and a cooler spot rather than a shorter time.

Sourdough and levain

A starter replaces commercial yeast with a mixed culture of wild yeast and lactic bacteria. The yeast raises the dough; the bacteria produce the acids that give the flavour, and the balance between them is set by temperature.

Warm and wet favours lactic acid, which reads as mild and yoghurty. Cool and stiff favours acetic acid, which reads as sharp and vinegary. For pizza, most people want the mild end: build the levain warm, use it at its peak, and keep the long stage in the fridge.

Use 10-25% of the total flour as ripe levain. Use it when it has domed and smells sweet-sour, not after it has collapsed and gone acetone. A collapsed starter still raises dough, but slowly and with a harsher flavour.

Everything takes longer. Plan on 4-6 hours of bulk before the cold stage rather than 1-2.

Autolyse

Not fermentation, but it belongs in the same conversation. Mix flour and water only, then leave it 30-60 minutes before adding salt and yeast. The flour hydrates fully and enzymes begin working on the gluten before you do.

The payoff is a dough that comes together with far less kneading and handles higher hydration without turning into soup. Above about 70% water it stops being optional.

Hold back the salt: salt tightens gluten and slows the enzymes, which is the opposite of what the rest is for.

Reading the dough

Time and temperature are inputs, not answers. Learn the two tests instead.

• The poke test: press a floured finger 1 cm into a proofed ball. If it springs straight back, it needs longer. If it fills in slowly and leaves a shallow dent, it is ready. If the dent stays and the surface looks bubbled and thin, it is overproofed.
• The windowpane test, for gluten rather than proof: stretch a piece of dough between your fingers. If it goes translucent before it tears, the gluten is developed. This is about kneading, not time.
• Overproofed dough is slack, sticky, smells of alcohol, and tears when you open it. It will not puff. Reball it, rest it 30 minutes, and accept a flatter pizza, or bake it as a focaccia where the collapse does not matter.
• Underproofed dough is tight, springy and resists opening. Give it another hour somewhere warm. This one is fixable by waiting, which is why it is the better mistake.

Freezing dough balls

Freezing works and it works well, which is not obvious. Ball the dough after the bulk, oil it, and freeze individually as early as possible so the yeast has not exhausted itself.

Thaw overnight in the fridge, then bring to room temperature for 2-3 hours as normal. It behaves like a slightly tired 48-hour dough.

Add about 20% more yeast to a batch you intend to freeze. Some of the culture does not survive the ice.

What else moves the clock

Temperature dominates everything: roughly, fermentation doubles in speed for every 8C warmer, which is why a 24C kitchen and a 4C fridge are five times apart in activity.

• Salt slows fermentation and tightens gluten. A 3% Neapolitan dough ferments noticeably slower than a 2% New York one at the same yeast dose.
• Sugar speeds it up at low doses by feeding the yeast directly, and slows it down above roughly 10% by pulling water away from it.
• Oil does not feed the yeast but it coats the gluten, giving a softer, more tender crumb and a dough that stays pliable in the fridge.
• Whole grain flour ferments faster: more enzymes, more minerals, more for the yeast to eat. Cut the yeast if you go past about 20% wholemeal.
• Chlorinated tap water is not the problem the internet says it is. Fridge temperature and yeast dose account for nearly every failed ferment.