The cruciferous (brassica) family boasts the cabbage, kale, cauliflower, broccoli, broccolini, brussels sprout, savoy, kohirabi and mustard greens. Humans started to genetically engineer these variants from one weedy Mediterranean plant, the mustard plant (brassica oleracea) 2–3000 years ago. The brussels sprout is a relative newcomer to the family, and records only show it being cultivated in earnest from the 18th century. Yes, it was in Belgium.
Starting from brassica oleracea, humans bred larger leaves to end up with kale; multiplied the flower buds to produce broccoli and brocollini; enlarged a terminal leaf bud to create cabbage; altered the nature of the flower buds to disable development and result in cauliflower; swelled the stem to create kohirabi; and, promoted the formation of multiple lateral leaf buds to create brussels sprouts. This makes all of these foods GMOs, but what an ingenious series of modifications of a single plant.
The cruciferous vegetables are characterized by pungent, bitter and sulphur flavours, and so it is a wonder that we eat any of them. However, they were cultivated because they grew in cold climates and during winter in many places, and were high in vitamins (particularly C). They provided much needed vitamin C over the dark winter months, and some forms (like the cabbage) kept very well. They could also be pickled and preserved for long periods of time (kimchi, sauerkraut etc).
Getting sufficient vitamin C over winter was a problem in higher northern latitudes, and by the end of winter, many people had used up their vitamin C stores (the body keeps about a 3 month reserve of vitamin C). This was a problem for the seafaring nations, because sailors who embarked on long voyages of discovery as the winter ended and the weather improved, were already low in vitamin C and in a pre-clinical state of scurvy. Even if they weren’t, scurvy could develop with sea voyages longer than 3 months. It was sauerkraut that Captain Cook fed to his men to stop them developing scurvy.
The strong flavour of these vegetables comes from their chemical defenses. These come in a two-pack; the stores of precursor chemicals and the enzymes to convert those chemicals into something bitter and undesirable to eat. The plants store this weaponry safely, until they are damaged (for example by being chewed by an animal or cut with a knife), in which case the chemicals and the enzymes mix, and the enzymes go about producing the repellant flavours.
Cooking inactivates the enzymes, and renders most of the cruciferous family palatable. But brussels sprouts come with a catch. They have very high amounts of the defensive chemicals in two main types (sinigrin and progoitrin). Sinigrin tastes bitter raw but becomes non-bitter when cooked, whereas progoitrin is non-bitter when raw but bitter when cooked. So it doesn’t matter whether we cook them briefly or slowly, brussels sprouts remain bitter. The chemicals are stored in higher concentrations in newly developing leaves, and so brussels sprouts are most bitter around (and in) their cores. Continued cooking brings out the sulphurous compounds.
Does any of this help prepare and cook brussels sprouts?
When cooked in a large pot of boiling water, the heat disables enzyme activity, and the large amount of water can leach out bitter flavours. However it also leaches out other nutrients and flavours, and by the time the inner core is cooked the outer leaves will be overdone. I’m sure we’ve all experienced this at some stage of our lives. In my experience, cutting a cross in the bottom of the stem doesn’t seem to help much.
Alternatively, accept that they are bitter and use sparingly when it is desirable to add a bitter flavour to a dish. An example might be to make a chiffonade and use as a garnish. I particularly like this approach (they can be grated on a small hand-held mandoline). Even though the sprouts have been cut and enzymes will be active, the flavour is better dispersed across the chiffonade and less noticeable (or they can be cooked). The chiffonade can be made from the outer parts of the sprout, avoiding the more bitter inner core.
The core can also be removed with an apple corer, the sprout blanched in very salty water then ice water. Fill with a complementary flavour (e.g. smoked salmon and sour cream).
Alternatively, to solve the inner-outer cooking problem, the leaves can be gently pried off and cooked on their own. For example, foam some butter in a pan, toss the leaves to coat, add a splash of water and cover (~5m or less) to cook. Or just blanch in boiling water.
Flavours can be added by initiating the maillard reactions and caramelization, either by shallow frying halved sprouts to brown the cut side (finishing the cooking in a moderate oven), or by deep frying the halves. David Chang (Momofuku) suggests tossing them in a fish-sauce vinaigrette. The fish sauce amplifies the umami of the fried sprouts.
The most common recourse is to mask the brussels sprout flavour with other ingredients. The most effective taste to counteract bitter is salty, so think about salty ingredients (bacon is traditional, and the fat will also mask flavour). An interesting thought is salted capers (the caper bush is related to the cabbage). Fat in the form of a cheese sauce is another common variant. Bulking with something mildly-flavoured, for example white beans, will disperse the flavour also. Bacon and roasting can be combined by draping bacon strips over halved sprouts. The bacon fat drips into the pan to help flavour and brown the sprouts.
Finally, flavour pairing attempts to match foods that share some chemical composition. Brussels sprouts (and other brassicas) have a surprisingly high level of omega 3 fatty acids, hence pairing with salmon. Their ties to the mustard family makes dijon another possibility to try.
There is something about the reputation of a brussels sprout that makes cooking it palatably an interesting challenge. I suspect that the dislike of a certain vegetable often has to do with the thoughtless, or habitual, way it is cooked.