Grilling bonito belly: firewood, charcoal or vine cuttings

Grilled bonito belly: beech wood, live embers and an exact point of doneness

Grilling bonito belly over embers is the ultimate test for any home barbecue. It is the fattiest part of the fish, one of the most expensive and the least forgiving: it takes a quick sear over very fierce embers and, the moment you look away, it turns into a rag. As for what fuel to use, how long to cook it and what to serve it with, there is technique, schools of thought and plenty of unresolved disagreements.

Firewood, charcoal or vine cuttings: what fire does the fish want

There is no consensus on the fuel, and saying otherwise would be a lie. One camp defends lump charcoal: it reaches higher temperatures, gives more stable embers and responds better when there is a lot of food to grill. Another prefers firewood —beech, oak, holm oak— because the smoky flavour of the last few minutes shows on the plate. And a third, the most frugal one, uses dry pruning branches and vine cuttings: material that would otherwise end up in a pile of waste.

Vine cuttings have a well-known mechanical flaw: their embers do not last long. That is why they are reserved for small cuts, like lamb chops, and holm oak takes over for everything else. One trick that keeps coming up: use the flames before they die down to grill peppers, spring onions or whole aubergines, which come out charred on the outside and perfect on the inside.

The exact point: when the backbone pulls away on its own

The clock lies. The reliable indicator is another: the fish is ready when the backbone comes away when you pull on it. And it is best to take it off a notch earlier, because residual heat keeps cooking it off the grill. With belly cuts the margin is minimal, hence the repeated advice of very fierce embers, a quick sear on each side and close watch on the grate.

To modulate the temperature there is a time-honoured trick: throw a handful of salt over the embers when flames appear. Finishing off an undercooked piece with a very hot sizzle of oil also works. Overcooking it, on the other hand, cannot be fixed.

Slow-cooked onion, mashed potato and Marina zarzuela playing in the background

The side dishes are also debated. Slow-cooked onion is the classic choice —with beech wood and, depending on the cook, even with a zarzuela (Spanish operetta) by Marina playing in the background, because some maintain that a table with a tablecloth and tradition tastes different—. To accompany the fish, a recurring option is mashed potato: boil, let cool, peel and mash with a splash of oil, a pinch of salt and a clove of garlic. The rustic variant: potatoes roasted with butter and coarse salt directly over the embers. The full recipe, with its order of steps and its ideal mashing point, is set out in detail.

One loose end remains that nobody has put figures to: how much fuel a fish really needs compared with boneless meat —the former uses proportionally more, because it has to be cooked properly all the way through— and what works out cheaper per diner, holm oak firewood or a bag of charcoal. The doneness of grilled bonito belly, on the other hand, is already settled: when the backbone pulls away, take it off.