While there is no strict rule on how long you can cook fish stock for, most agree that you could end up with a cloudy, chalky broth if it’s left on the stove too long. Anything longer than 35 minutes also tends to leave a bitter taste, affecting the overall flavour of your soup. Keep in mind that it depends on the type of fish bones you use and some will need a longer cooking time than others to fully extract its fishy goodness. In general, a good rule of thumb is to turn off the heat when the head and bones start to fall apart.
While this largely depends on the type of fish that you use, the best soups will have a distinct, but very delicate, fish flavour. You’re looking for an oh-so-subtle hint of fish essence that is perfectly balanced by the soup’s other ingredients.
There are three culprits here. Overcooking your fish stock is the most common one, and anything longer than 35 minutes on the stove will start to develop a bitter flavour. If the fish’s gallbladder was pierced during the cleaning process and leaked onto the flesh, even the slightest remnant will cook into your broth and leave a bitter aftertaste. The fats of a not-so-fresh fish could also add a bitter note to your soup, not to mention pose a health risk if the ingredient is not at its freshest best.
With a fragrant and versatile stock as its base, this soup can be completely transformed every time you make it. The recipe’s lean white fish can be traded with any other catch of the day that has a high- to moderate firmness like rainbow trout, salmon, or mackerel. Make sure to avoid delicate varieties like sole as they tend to disintegrate in the broth. Adding seafood, anything from shellfish and molluscs to crustaceans is also an easy way to reinvent your dinner.
The bright green fennel and leek topping, combined with golden-brown croutons, should add all the colour you need to this recipe. For an even more impressive dish, why not turn the soup into a bisque by reducing it to a thicker consistency and serving over squid ink pasta? The contrast of inky black strands and white fish will be as much a feast for the eyes as for the palate. Another great way of adding both flavour and colour is safran. A few strands will add a luxurious taste and give the dish a wonderful yellow colour.