Boiling has always been a handy cooking technique. When water boils, it is 100 degrees. A clear measure. When preparing fish, cooks often use the poaching technique. We poach in water which is just coming to the boil but not bubbling. The temperature then varies between 90 and 95 degrees.
However, boiling and poaching are not necessarily the best techniques for preparing fish. This is to do with what happens to the proteins in fish. Fish gets its ideal texture when prepared at a low temperature. The fish remains juicy, firm and tender. The moisture from the fish is retained in the protein molecules.
When fish is exposed to extreme conditions, such as acid or a high temperature (above 80 degrees), its composition won’t change. But its natural structure will. Certain connections between protein molecules in the fish are broken and new ones are formed. The proteins will congeal. We call this denaturation. Too much denaturation and your fish will become tough, dry and lose its natural structure.
Fortunately there are two techniques which enable you to cook your fish at a low temperature in a controlled way:
1. Steaming
2. Sous-vide
Try steaming a lovely fresh piece of salmon filet without the skin for around 25 minutes in the steam oven at 70 degrees. If you rub some coarse mustard with some sugar and freshly chopped dill into the fish, you are in for a pleasant, super soft, juicy surprise.
Or vacuum pack halibut or cod in a sous-vide bag with some sprigs of dill, a few slices of lemon and a drop of extra virgin olive oil. Steam the fish for 45 to 60 minutes at 65 degrees. The result is beautifully tender and buttery soft fish.
And if you really enjoy a crispy, savoury crust on your fish, no problem. Pat the buttery soft fish dry and give it a short ‘burst’ in the frying pan, grill pan or Teppan Yaki grill.