What you need
Cooking oil
Potatoes
Wok or large pan
Thermometer
CRISPINESS is one of food’s most prized properties, but why do we find it so appealing? It might be because it often arises when raw ingredients become delicious and nutritious cooked food. also speculates that we have learned to associate crispiness with high-fat foods, which we find particularly rewarding.
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The ultimate crispy and rewarding food has to be the chip. To be clear, I mean the hot, fried sticks of potato, not the thin discs, which are called crisps in the UK.
When raw chips go into hot oil, water inside them evaporates. Some water vapour escapes, forming bubbles in the oil. Below the surface, the rest of the water vapour is trapped, steaming the inside of the chip to cook it.
Meanwhile, starch starts to create the chip’s crispy crust. Potato cells are packed with starch granules, which swell and burst during cooking. The starch molecules then dissolve and form a gel, which hardens to make the crust. But there is a limit to how thick this will get during one spell in the fryer.
This is why chips tend to be fried twice. Some of the gelatinised starch recrystallises after the first fry, making the crust more robust. On the second fry, more starch granules burst, creating more gel and a thicker crust.
For frying at home, a wok is the ideal vessel: its flared edge makes it less messy, easier to reach into and less likely to boil over. Use a thermometer to make sure the oil reaches 150°C for the first fry. Up to 200°C is good for the second fry to get maximum crispiness.
The double fry gives pleasingly crisp results, but some go further in search of perfection. I put two chefs’ methods to the test. For his famous triple-cooked chips, Heston Blumenthal boils the chips for 20 to 30 minutes before frying, so they are almost falling apart. This creates fluffy edges and plenty of gelatinised starch for the crust. Before and after the first fry, the chips are put into a dehydrator to dry out. To get similar results at home, Blumenthal recommends an hour or so in the freezer. Ice crystals damage the potato cells and make it easier for steam to escape during frying.
This method works a treat for thick-cut chips, but thin ones disintegrate with 20 minutes of boiling. For perfect skinny fries, Kenji Lopez-Alt boils them for 10 minutes in water acidified with vinegar (about 20 millilitres per litre of water) before double-frying. This strengthens their pectin, a sugar that glues the potato cells together, giving a firmer structure.
I found Blumenthal’s chips, with their spectacularly hard edges, the most satisfying, and well worth the effort. If you are short of time, consider an alternative approach. In a now famous experiment, Spence played crunchy sounds to crisp-eating volunteers through headphones – making the crisps seem 15 per cent crunchier.
For next week
Soya beans
Cheesecloth
Magnesium salts
Container with holes for drainage
Next in the series
3 Science of crispiness
4 Tofu and Sichuan pepper Make bean curd for Chinese New Year
5 Gravlax and curing
6 Tempering chocolate
7 Umami and flavour
8 Perfect pancakes
9 Kimchi and fermentation
10 Sourdough bread
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