Tier 1 · Prep

TO ZEST

Taking the coloured outer skin of a citrus fruit, where nearly all of its aroma lives, and none of the white beneath it.

Why it works

A citrus fruit keeps its aromatic oils in glands in the coloured outer layer, the flavedo. The juice supplies acid and sugar and almost no aroma — which is why a dish made with juice alone tastes sour rather than of lemon, and why zest transforms it. Directly beneath is the albedo, the white pith, which contains limonin and naringin: bitter compounds that are not volatile and do not cook out. So the entire technique is a depth question, taking one layer and not the next. Rubbing zest into sugar with the fingers ruptures the oil glands mechanically and disperses the oil through the sugar, which both extracts more of it and preserves it, since those oils evaporate readily once exposed.

How to tell

• The zest should be uniformly coloured with no white on the underside — turn a piece over and look.
• The fruit underneath shows white where you have been, and you stop the moment white appears.
• The smell is immediate and strong as the glands rupture; if the room does not smell of citrus you are not getting much.
• Zest rubbed into sugar clumps slightly and turns faintly coloured and fragrant.

When it goes wrong

The finished dish is bitter.

Pith taken along with the zest. Bitterness from albedo is permanent and gets stronger as the dish sits.

Barely any citrus flavour despite plenty of zest.

Added early and cooked. The aromatic oils are volatile and mostly gone within a few minutes of heat; zest goes in late, or off the heat.

Long shreds that are unpleasant to eat.

Wrong tool for the purpose. A microplane gives fine zest that disappears; a peeler gives strips meant to be infused and removed.

Waxy taste.

Unwashed fruit. Most citrus is waxed, and the wax sits exactly where the zest is.

Recovering it

Bitter zest cannot be removed once it is in a batter or a sauce — the honest options are to dilute it into a larger batch or start again, and the lesson is to zest before juicing so you can taste a pinch first. Aroma lost to cooking can simply be replaced: grate fresh zest in at the end, since the technique costs thirty seconds. Always zest before juicing — a squeezed lemon is very difficult to zest.

Where to practise it

It carries to

Recipes using it

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