Week 4: Fat, and the cold
The week 4 lecture — what 5% olive oil does to a gluten network, and what two days at 4 °C do that three hours at 26 °C cannot
15 March 2027
Two days in the fridge, ninety minutes on a bench, twenty in the oven. Almost all of the work in a focaccia happens while you are asleep, and the two things that make that possible are 5% olive oil and 4 °C.
Oil is a lubricant before it is a flavour. At 5% it films the gluten strands as they form and keeps some of them from linking up, so the network still holds gas but has lost some of its snap. That is why focaccia tears short where a baguette strings, and why the same dough stays soft the next day. The same substance behaves completely differently once it sits between the dough and the hot metal. Oven air barely touches a pan base. Oil fills the gap, so heat arrives by contact, and a base sitting in oil is at pan temperature within a few minutes where a base sitting in air takes most of the bake to get there.
The cold half of the lecture is an argument about rates. Yeast and the flour’s own enzymes both slow down at 4 °C, and they slow down by very different factors. Yeast gas production drops by something close to an order of magnitude; amylase and protease keep working, unhurried, breaking starch towards maltose and protein towards amino acids. So over two days you accumulate sugar, aroma and browning potential far faster than the yeast can consume them. The dough still rises — a fridge that runs warm will overflow your tub — it just rises slowly enough for the chemistry to get ahead. Three hours at 26 °C gets you comparable volume and a fraction of the taste.
Most of the rest follows. A fully proofed dough has spent most of its elasticity, so a fingertip pressed to the pan base leaves a hole that has nothing much left to close it. An under-proofed one still has spring, and the dimples fill in while you watch.
The brine is the step students skip. Twenty grams of water, twenty of oil and two of salt, whisked hard, is an emulsion that lasts about a minute before the oil floats again — which is why it goes on immediately. The water is the working part. It settles into the dimples and boils off there, holding those spots near 100 °C for the first two or three minutes of the bake, so the top stays soft and pale while the edges and the base get on with browning.
Three failures are worth naming in advance, because all three are decisions rather than accidents. Dough dimpled straight from the fridge is stiff, fights the fingers and tears. Dough dimpled before it is properly proofed loses every hole. And a base that came out pale and greasy was under-oiled, or baked too cool, or both: at 200 °C the oil still works, it just browns the base more slowly than the crumb dries.
Outline#
- oil in the mix: filming the gluten, and why it goes in after the dough forms
- oil under the dough: contact heat, and why the base fries
- 24 to 48 hours at 4 °C: yeast slows further than the enzymes do
- dimpling a warm, proofed dough to the base of the pan
- the brine: a one-minute emulsion, and what the water is for
- the three failures — cold dough, under-proofed dough, an under-oiled pan
Teaching team
- Idris Fenn — tutor