Tender herbs are a key part of my cooking. Unfortunately, not all herbs last all year, and I don’t like drying herbs from the garden (with the exception of fennel seed). I never like the taste of dried leaves – it always seems dusty. I know it’s not true but I just don’t like the flavour or texture.
So I make oils for the winter. I freeze the blitzed herbs in cubes too, using a little veg oil and store coriander, basil and tarragon that way. But tarragon in particular makes a fabulous oil.
So, how do you do it? easy. Pick the plant before it wilts and the leaves die pack, just before it goes. For basil I take the whole plant, stems and all. For tarragon when the leaves start to die I harvest 90% of whats there. The plant then just sits over winter and it you keep it frost free it will come back happily next spring.
In both cases I blitz in olive oil and steep in luke warm oil for a few hours or overnight. Avoid heating the oil too much as it changes the texture and taste – turning cis-unsaturated oil chains to trans. These trans fats are not as good for you, and do less to lower cholesterol. So cool steeping is best. When its good and smelly with the herb strain through a fine sieve and muslin.
If you only used the leaves you can still use the leaves in oil as a paste, for basil it’s ideal to make pesto, for tarragon I just freeze and note it’s in olive oil.
For the oil you’ve made leave it to stand for a day or three then decant it. The reason is that you will see a small amount of brownish water at the bottom – this will ferment over time and produce a vinegar that will ruin the flavour of the oil. So you want to decant the oil and leave the liquid. The oil then stores for months.
The only way to avoid this issue is to pasteurise the oil (heat it to at least 72c for 15 sec) – but this also changes the taste, and degrades the flavours of the herb and benefits of the oil. Up to you, but I prefer to fiddle a bit to keep the taste and avoid handling hot oil wherever possible.
When you use infused oils, add them at the end, as a drizzle or to coat the pasta before mixing in the sauce – less cooking means more flavour…