Taking the coloured outer skin of a citrus fruit, where nearly all of its aroma lives, and none of the white beneath it.
Technique at a glance
A compact visual model of the lesson. Use the full mechanism and success criteria below when you practice.
Concept
Taking the coloured outer skin of a citrus fruit, where nearly all of its aroma lives, and none of the white beneath it.
What changes
A citrus fruit keeps its aromatic oils in glands in the coloured outer layer, the flavedo.
What good looks like
The zest should be uniformly coloured with no white on the underside — turn a piece over and look.
Practice counts when you cook
Reading this brief does not change your School state. Finish a real practice dish in Cook mode and log the cook; that cook is the evidence that advances the skill.
What to focus on
Mechanism
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.
Success criteria
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.
Failure guards
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.