Week 8: The skin set in water

The week 8 lecture — why a stiff dough behaves nothing like a wet one, and what ninety seconds in a pot does to the starch on the outside of a ring

12 April 2027

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A bagel is the only bread this semester that is cooked twice, and the first cooking is the one that decides what it is. Everything else — the stiff dough, the malt, the night in the fridge — is there to build something that can survive ninety seconds in boiling water and be improved by it.

Start with the hydration, because it runs against the instinct week 3 built. At 55% there is barely enough water to hydrate the flour, let alone to lubricate the gluten strands while they slide past each other and link up. Mixing time goes up rather than down. The payoff is a crumb with small, tight, evenly distributed cells, which is what chew actually is: a dense continuous gluten network with nowhere much for your teeth to fall through. High-gluten flour at 13–14% protein supplies the extra glutenin that network needs, and it is why a bagel made on 11.5% bakers’ flour comes out pleasant and wrong.

Barley malt syrup is about two-thirds maltose. Non-diastatic syrup has been cooked, so its amylase is dead and it acts as flavour, colour and yeast food only. Diastatic malt still carries live enzyme, and week 7 already showed you where that enzyme does its work: not in the cold, where it is close to dormant, but in the first minutes of the bake, once the starch has gelatinised and before the heat denatures it. A trace is useful. More than about 1% of flour weight and you cut enough starch to leave the crumb gummy. In a formula with no other sugar, the malt is also most of the reason the crust browns at all.

Week 4 made the case for the fridge as a flavour tool, and that argument holds here unchanged. What is new is the mechanical job. Twelve to twenty-four hours at 4 °C stiffens the fat-free dough and, left uncovered, dries a thin skin onto the surface. A ring with that skin keeps its shape in moving water. One straight from a warm bench slumps and loses its hole.

The float test is a direct measurement, not a ritual. A dough’s density falls as the gas fraction in it rises, and a ring floats once enough of its volume is carbon dioxide. You are reading proof state off Archimedes rather than off a fingertip dent, which is more reliable on a cold, firm dough where the dent test barely works.

Then the boil. Above about 60 °C starch granules take up water, swell and rupture, and the gelatinised starch at the surface fuses into a continuous gel layer perhaps a millimetre thick. That layer does three separate things. It is a physical lid, so oven spring is cut short and the crumb sets dense. It is smooth, sugar-rich and tacky, so it browns to a gloss and seeds adhere. And it is thin enough that a hot, dry oven at 220–230 °C dries and colours it into a crust rather than leaving it rubbery — which is also why steam is the wrong tool this week, and why four minutes in the pot turns a gloss into a wrinkle.

Alkalinity sharpens all of it. Raising the water’s pH deprotonates the amino groups on the surface proteins, which makes them far more reactive in the Maillard reaction, and it degrades surface starch besides. Bicarbonate at pH 8.5 gives a darker crust and a faint pretzel flavour; lye at pH 13 gives the mahogany you see on a good pretzel, along with the handling risk that keeps it out of a teaching kitchen.

Outline

Teaching team