Vol. XX · Vegetables, Fruit and Legumes Plate 7 of 12brassicas, cabbage, broccoli, Brussels sprouts, cauliflower, mustard oils, glucosinolates, isothiocyanates, sulphur smell, hydrogen sulphide, overcooked cabbage, kimchiMF

Cabbages and Their Smells.

The smell of school-dinner cabbage is not the smell of cabbage. It is the smell of cabbage boiled for twenty minutes.

The cabbage family — cabbage, broccoli, cauliflower, kale, Brussels sprouts, 白菜, 芥兰, mustard greens, radish — defends itself with glucosinolates, sulphur compounds kept apart from an enzyme, myrosinase, until the plant is cut or chewed. Then they make isothiocyanates, the "mustard oils": the bite of raw radish, mustard and wasabi, the pleasant pungency of raw cabbage. Cooking briefly softens them; cooking long brings a second, worse chemistry, as heat breaks sulphur-containing amino acids into hydrogen sulphide and di- and trisulphides — the smell of rotten eggs and old boiled cabbage.

That second smell grows steeply with time: in classic measurements the hydrogen sulphide from boiling cabbage roughly doubled between the fifth and seventh minute. So brassicas are cooked fast — shredded and stir-fried, cut into florets and steamed or blanched, roasted hot until browned — and served when just tender. The other way is deliberate: kimchi and sauerkraut ferment them (XIV.4), and long, gentle braising in fat turns cabbage sweet, silky and mild. The workshop boils four cuts.

Below: the softening at the centre of four brassica cuts boiled for the minutes you choose (thermal bench, course vegetable kinetics), and a teaching index of the sulphur smell rising with the square of the cooking time.

What you will learn

Explain the two smells of brassicas.
Cook brassicas before the sulphur smell builds.
Choose a cut for a fast cook.
Use long gentle cooking and fermentation on purpose.

Workshop

Thermal bench: shredded cabbage as a 3 mm slab, a cabbage wedge as a 30 mm slab, broccoli florets as 12 mm cylinders and Brussels sprouts as 25 mm spheres, from 20 °C in boiling water, softening tracked at the centre with the course rate; tender taken as the centre half-softened. Smell index: (minutes ÷ 5)², shaped on the reported doubling between minutes 5 and 7 of boiling.

Cut small, cook fast, or cook long on purpose

In this model shredded cabbage is tender after about 3.3 minutes in boiling water, broccoli florets after 5.3 and whole sprouts after 8, while a thick wedge is still firm at the centre after twenty. On the smell index those times score 0.4, 1.1 and 2.8, and the wedge at twenty minutes 16: many times the sulphur of the shreds, and still not done. The cut is the most powerful control — halve sprouts, cut stems thin, shred cabbage — and the pot should be big and uncovered so the gases escape.

Methods that suit brassicas: stir-fry shredded cabbage or 芥兰 with garlic in a hot wok for two or three minutes (XV.4); blanch broccoli florets for two minutes and dress them; roast halved sprouts and cauliflower at 220 °C until browned at the edges (XX.5), where browning flavours replace sulphur ones; or braise cabbage slowly in butter or bacon fat, covered, at a low simmer, where its sweetness comes out. Crushing raw cabbage with salt makes slaw and kimchi, whose mustard oils turn into the sour, savoury notes of fermentation (XIV.4).

At the stove

Boil cabbage wedges and shreds in two pots and smell each pot at 3, 6 and 12 minutes. Note when the smell turns from fresh to sulphurous.

Wasabi, horseradish and mustard get their heat from the same mustard oils: freshly grated wasabi peaks a few minutes after grating as the enzyme works, and then fades — which is why it is grated at the table on a sharkskin grater, and why mustard powder is mixed with cold water and left ten minutes.

Terms

Glucosinolates: Sulphur compounds in brassicas that become mustard oils when cut.
Isothiocyanates: Mustard oils: the pungency of raw mustard, radish and wasabi.
Hydrogen sulphide: The rotten-egg gas released by long-boiled brassicas.
Myrosinase: The brassica enzyme that releases mustard oils.

Brassicas make mustard oils when cut and sulphur gases when overcooked; the smell grows steeply with time. Cut them small, cook them fast in an open pot — or braise and ferment them on purpose.

Sources

A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.