Pastry
A doughnut is cooked by oil and the pale ring proves it
Deep frying is a way of delivering heat rather than a way of adding fat, and the crust, the untanned band around the middle and the greasiness all follow from how water leaves the dough.
By Amrita Kohli4 min read
Oil is a heat transfer medium before it is an ingredient
Frying looks like the least precise thing a pastry kitchen does and is in fact one of the more controlled. Hot oil transfers heat to a surface enormously more efficiently than hot air does, because a liquid carries far more energy per unit volume and moves against the food continuously. That is the whole reason a doughnut cooks through in a couple of minutes when a bun of the same size needs a quarter of an hour in an oven.
The oil is also hotter than an oven is at the surface of the food, though not hotter as a setting. Frying is generally done somewhere around a hundred and seventy-five to a hundred and ninety degrees, and every part of the dough in contact with the oil is at that temperature immediately. In an oven the surface has to be warmed by air and radiation, which takes time and never reaches the same intensity of contact.
Escaping steam is what keeps the oil out
The interior of a frying doughnut cannot exceed a hundred degrees while it still contains water, for the same reason a boiling pan cannot. What that water does as it turns to vapour is the interesting part: it forces its way outwards through the dough and out of the surface, and that outward flow physically opposes any oil trying to move inwards. The bubbling around a frying doughnut is that steam arriving in the oil.
This means a properly fried doughnut absorbs much less oil than people assume, and it explains why the oil temperature is the critical variable. Oil that is too cool cooks slowly, the steam production is feeble, the outward pressure is weak and oil soaks in — which is exactly the greasy, heavy result everyone recognises. Oil that is too hot browns the outside before the steam has finished its work inside, giving a dark shell around raw dough.
The pale ring is a record of where the dough floated
A ring doughnut has a distinct untanned band around its circumference, and it is one of the more legible pieces of evidence in baking. The dough is less dense than the oil, so it floats, and the band marks the line where it sat at the surface. That part of the dough was in contact with air and escaping steam rather than with hot oil, so it never reached browning temperature.
It is also a quality marker in the trade. A wide, clean band means the doughnut floated high and expanded well, which indicates a properly proofed dough and a correct oil temperature. A thin or absent band means the dough sat low, was too dense, or was turned too soon. Reading the ring tells you about the proof rather than about the frying, which is why it is worth looking at before anything is tasted.
Most oil absorption happens on the way out
The counter-intuitive part is that a doughnut takes up a good deal of its oil after it leaves the pan. While it is frying, steam is streaming outwards. When it is lifted out, the interior begins to cool, the vapour inside condenses, and the pressure inside the crumb falls below the pressure outside it. Any oil clinging to the surface is then drawn into the porous structure by that difference.
Which is why draining matters and why draining while hot matters more. Getting surface oil off in the first moments — on a rack rather than on paper, so it runs away rather than pooling — removes it before the suction develops. It is also why a doughnut tossed in sugar straight from the fryer eats less greasy than one sugared later, since the coating goes on before the surface film has had time to be absorbed.
Yeasted and chemically raised doughnuts fail in different ways
A yeasted ring is a proofed dough with an open structure, and it wants a slightly lower oil temperature and a longer time, because there’s a lot of gas to expand and a lot of interior to set. Over-proofing shows up dramatically in the fryer: a dough that has gone too far collapses when its structure meets the heat, and it absorbs oil through the flattened crumb.
A cake doughnut is a soft batter raised chemically, and it behaves quite differently. The leavening releases quickly on contact with heat, so the crack that opens across the top is the batter expanding faster than its surface can set — the same event as a cracked muffin, at higher speed. It needs a hotter oil and a shorter time, and it absorbs more oil regardless, since a batter has more surface irregularity and a less continuous crust. Neither is a better doughnut. They are different constructions asking for different conditions.
Common questions
Why are my doughnuts greasy?
Almost always oil that was too cool. Steam leaving the dough is what holds oil at bay, and a slow, cool fry produces feeble steam and a long exposure, so the oil moves in. Check the temperature between batches, since adding cold dough drops it sharply and it needs time to recover.
Why is there no pale ring on mine?
The dough sat low in the oil rather than floating high, which usually means it was under-proofed and too dense, or the pieces were turned before the first side had set. A well-proofed ring floats immediately and shows a clean band where the oil surface met it.
Can the same recipe be baked instead?
It can be baked and it will be a decent bun, but it won’t be a doughnut. Oven heat browns the whole surface, dries the crust and produces no ring, and the crumb sets more slowly. The characteristic thin, tender crust comes from very fast heat transfer that an oven cannot supply.
Senior writer, The Last Bite
Amrita has written about baking basics, chocolate & sugar, frozen for most of the last decade and is unreasonably interested in the detail nobody else checks.
