Ask any fryer what makes a good chip and you will hear about oil temperature, blanching and the second fry. Ask a supplier and the answer is shorter: the potato. Choose the wrong variety and no amount of technique will rescue it — the chips come out pale, greasy, or collapsing into mush. Choose the right one and everything else gets easier.

Starch and sugar decide almost everything

A potato is mostly water and starch. The starch is what gives a chip its fluffy middle, and what dries and swells in hot oil to form a crisp shell. Potatoes with plenty of it — the ones we describe as floury or mealy — take up less oil, hold their shape, and give you that contrast between brittle edge and soft centre.

Sugar matters just as much, in a different way. When a cut chip hits hot oil, sugars on its surface react with amino acids and brown. A little of that gives you an appetising gold. Too much and the chips darken before the middle is cooked, tasting bitter and looking burnt even when they are not. This is why fryers talk about chips that "went dark on Tuesday": the potatoes changed, not the fryer.

Freshly lifted potatoes and cold-stored potatoes both carry more sugar. Left somewhere warmer for a week or two, those sugar levels fall and the fry colour evens out. That waiting period — conditioning — is one of the quiet skills of running a good chippy.

The varieties behind the counter

Walk into a wholesaler and you will see the same names year after year. Each has a personality.

• Maris Piper — the British default. Floury, dependable, widely grown, and the potato most fryers picture when they say "chipping variety".
• Agria — long and oval with high dry matter and buttery flesh. Excellent for thick-cut chips.
• Markies — high dry matter and one of the best storers, which is why it turns up in fryers late in the season.
• Sante — a sturdy all-rounder, grown as much for its disease resistance as for its frying.
• King Edward — floury and full-flavoured. Usually sold as a roaster, but it makes a fine chip in careful hands.
• Pentland Dell — an old chipper's favourite, still grown for chips and roasting.
• Innovator — the workhorse of frozen fry production: long, uniform, reliable.
• Estima — the most common all-rounder in the UK. Lower dry matter, so it can give softer, oilier chips if fried hard.
• Lady Rosetta and Lady Claire — crisping potatoes, used for very crisp, thin-cut chips.

Shops rarely buy one variety all year. A typical contract names a variety, or a short list of approved ones, plus a specification the grower has to hit.

Why your chips change in May

Maincrop potatoes are lifted from late summer into autumn, then stored in cooled or ambient sheds for months. Early and new potatoes arrive in late spring and early summer: low in starch, high in sugar, waxy in texture. They are wonderful boiled with butter and hopeless in a fryer.

So chip shops swap. A shop might open the season on a stored line, move to a fresh-crop variety in summer, and shift again the following spring as sugars rise and potatoes begin to sprout. Fryers compensate as well: a lower oil temperature, a longer blanch, or a short soak to rinse surface sugar off the cut chips. Customers notice the difference. Same shop, same oil, same fryer, different chips.

What a buyer checks before signing

1. Dry matter — high enough for a crisp shell, not so high the chips break apart.
2. Reducing sugars — tested before the load leaves the farm, because this is what drives dark fry colour.
3. Size grade — a fairly narrow band, with smalls and oversized potatoes screened out, so the cutter produces long chips rather than stubs.
4. Shape and eyes — oval to long with shallow eyes, which cut into clean, even strips.
5. A clean sample — no greening, bruising, hollow heart or growth cracks, all of which turn into black patches in the fryer.
6. Storage potential — essential if the crop has to last until spring.
7. A fry test — a handful fried and checked against a colour chart before anyone commits to a tonne.

Price and availability still matter, but they come after the fry test. A cheap load that produces dark chips costs more in the end than a good one.

Buying potatoes for chips at home

The same rules apply in a domestic kitchen. Look for floury varieties: Maris Piper, King Edward, Rooster or Kerr's Pink are safe bets. Salad potatoes such as Charlotte or Jersey Royals will never crisp, however you treat them.

Buy loose if you can, and pick firm, even-sized potatoes with no green patches. Store them cool, dark and ventilated — a cupboard rather than the fridge. Cold storage pushes sugar levels up, and sugary potatoes fry dark. When you cook, cut the chips to an even size, rinse them under cold water to wash off surface starch, then dry them thoroughly before they go anywhere near oil. A first low-temperature fry followed by a hotter one gives you the fluffy-then-crisp result that a good chippy gets from its range.

Matching the potato to the plate

There is no single best chipping variety. The right answer depends on what you are frying, the time of year, and how much consistency matters to you. A thin, crisp chip for a Friday night deserves a different potato from a fat, fluffy one served with gravy.

What separates a good chip shop from an average one is not secret knowledge. It is attention: knowing what is in the sack this week, tasting as the season moves, and adjusting before the customer notices. If you run a shop, ask your supplier which variety is in the load and when it was lifted. If you cook at home, buy small and buy often, and let the fryer tell you what the cupboard is holding.

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