Ask Peter curing fish

I love gravadlax and am wondering if you can cure other fish in this same way? Are there fish that will or won’t work? And what would be a general rule for how long something like this will keep? Bill

You can pretty much cure anything at all. The common cold is somewhat elusive, but pretty much all fleshy fish can be cured. Gravadlax, or gravlax, is what I’d call a soft and loose cure. The salmon remains moist and almost raw in the middle and the curing process can take anything from 24-72 hours. The salt and sugar mixture is usually just flavoured with dill, although beetroot is becoming a popular addition. Adding toasted caraway seeds gives it a hint of Nordicness (which is also becoming more popular) but crushed toasted coriander seeds give a more pleasant citrusy result. You can add grated ginger, chopped lemongrass, chilli or lime leaves, and various spices from star anise to vanilla to good effect.

The chemical reaction that happens when you cure a protein in salt or sugar (or more commonly, both) is that the moisture is literally sucked out of the protein by the salt and sugar crystals. They love nothing more than moisture (that’s why a meringue will go soggy if not kept in an airtight container, and why those annoying salt shakers block up) and so they serve a good purpose in food preparation. They also kill surface bacteria which is why salted meats, mutton birds and the curing of smallgoods always involve salt. Last year I went to a jamon Iberico producer near Jabugo in Spain. The first part of their long curing process (of up to 24 months) involves burying the butchered pig’s legs in coarse salt. This kills all surface bacteria and renders the meat “clean”, as it were.

Bad bacteria is a disaster when curing proteins. It will spoil the protein, which will taste really bad, but it can also prove lethal — so it’s a serious issue.

Bacalao is a salted and dried cod which is hugely popular in Spanish and Portuguese cuisine although it also appears in many Mediterranean dishes such as France’s brandade — a “pate” of pounded cod, bread, olive oil and garlic. Centuries ago, before refrigeration was invented, salting, then drying in the near-Arctic air was the only way of transporting cod from the fishing grounds of the North Sea to Spain’s mainland. People need protein to survive, so this smelly ingredient became hugely important in trading.

You can cure any fish, pretty much — as well as any meats that are okay to eat rare. Years ago at Wellington’s original Sugar Club, I was curing kahawai, hapuku, snapper and trevally, alongside beef fillet and duck breasts. The thicker the piece of protein or fillet, the longer it would need curing, and I would cure to various degrees. So a thin trevally might be immersed in a mixture of honey and soy (replacing sugar and salt) for 10 hours, before being wiped off, thinly sliced and served draped over a soba noodle, toasted sesame and avocado salad. Cured yellow-fin tuna loin (cut into 3cm square baton shapes) or beef fillet might be cured for seven days in a mixture of rock salt, brown sugar, tonnes of chopped red chillies and ginger and a slug of whisky or rum. So, you can be quite experimental, and so long as you kill off that bacteria you should be fine!