Deep frying
A two-way exchange: water leaves and fat arrives. How much water leaves depends on the oil temperature, and how much fat arrives depends on how fast that water left. Which is why cool oil both dries less and greases more.
Change them and see
The oil holds its temperature
There is enough oil that cold potato drops it only a few degrees and it recovers at once. The crust forms and the fat stays out.
In order, minute by minute
Not a list of steps but a timeline: each one carries the minute it happens at and the temperature it happens at. Changing the order changes the result, and this shape is why the engine can say so.
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0 minutes
Cut the potato, soak it in cold water, then dry it thoroughly.
The water takes the loose surface starch, which is what burns and darkens. Drying is not optional: a wet surface has to boil its water off first, and the oil cools while it does.
What to look for Until the towel stays dry and there is no shine on the surface.
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30 minutes 150 °C
First fry: 150 °C, no colour, until it gives to a squeeze.
This stage is about cooking the inside. The low temperature gives the heat time to reach the middle and the starch time to gelatinise. Colour is not wanted here: 150 °C is below Maillard, deliberately.
What to look for It should give slightly under a finger, and still be pale.
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40 minutes
Drain it and let it cool right down. Do not rush this.
As it cools the surface moisture evaporates and the gelatinised starch firms into the beginnings of a shell. The crunch of the second fry comes from that shell rather than from the second fry itself.
What to look for Down to room temperature, or into the fridge if you have time.
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1 hours 180 °CCritical point
Second fry: 180 °C, until it goes golden.
Between 170 and 190 the surface water flashes to steam fast enough to push outward, and that pressure is the shield keeping the oil out. Above 140 Maillard runs as well, and that is where the colour and the roasted taste come from.
What to look for The bubbles grow larger and fewer, which means the surface water has gone. That is the moment to lift it out.
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1,1 hours 70 °C
Into the strainer and salt it at once.
Salt only clings to a hot, faintly oily surface. Once it cools the surface dries and the salt falls off. Onto a rack rather than paper: paper traps the steam and softens the crust you just built.
What to look for The salt should stick to the surface rather than collect on the plate.
The numbers that decide it
The oil holds its temperature
The crust forms for as long as the oil can hold its temperature. Crowding the pan ruins the result without changing a word of the recipe.
The oil holds its temperature
Fried at the right temperature a chip takes up roughly eight to ten per cent of its weight in fat. Let the oil fall below 150 and that can double.
Below 140 °C no colour arrives at all: the food cooks and stays pale. Colour comes from Maillard, not from time.
What is happening in the pot
- ideal 0.8–1.5% Salt · 0.47% Low. Everything reads flat and nothing steps forward. Held in the system
What happened, why, and what to do
Some of these can be saved and some cannot. Writing up the second kind as though it were the first costs somebody another twenty minutes.
01 Greasy and soggy ⌄
Why
The oil was below 170, or the pan was too full. The steam shield never formed and the fat went in.
Can be saved
Partly: another minute at 190. Some of the absorbed fat comes back out, not all of it.
02 Cooked but never coloured ⌄
Why
The oil stayed below 140 °C and Maillard never began.
Can be saved
Take the oil to 180 and give it another minute or two. The inside is already cooked; only the surface is missing.
03 Dark outside, raw inside ⌄
Why
Fried once, too hot. The surface was finished long before the heat reached the middle.
Cannot be saved
This batch is gone. Next time fry it twice: cook at 150, cool, then colour at 180.
04 The oil is bitter, dark and foaming ⌄
Why
The oil passed its smoke point, or has been used too often. As free fatty acids build up the smoke point falls, so each use spoils more easily than the last.
Cannot be saved
The oil goes, and so does what was cooked in it. The bitterness has already moved into the food and does not come out.
The safety check does not know the following. That is not the same as nothing being wrong — it means nobody looked, and anything meant to keep at room temperature has to be measured rather than assumed.
- Water activity
This is a model estimate rather than a measurement. How far each threshold behind it has been checked is below; fourteen of the fifteen still have no source on file, and saying so is better than not.
engine 1.0.0 · ruleset 2026.09.1 · confidence medium
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