Pesto genovese is four ingredients and one tool. People skip the tool, and that is why home-made pesto so often turns dark and bitter.
First things first: the mortar is not obsolete
The word pesto comes from pestare, to crush. A marble mortar and a wooden pestle grind the leaves against a rough surface and press the oils out of the cells without tearing them apart. A stick blender does the opposite: the metal blade cuts thousands of surfaces a second, and oxidation starts immediately. The enzyme polyphenol oxidase in the basil reacts with the air and turns the leaves greyish black, in the same way as a cut apple. The blade also gets warm from friction, and the heat speeds the whole thing up. The result tastes more bitter than it needs to.
If you do not have a mortar, blitz briefly and in pulses, with the bowl and blade chilled in the freezer first. But the order is the point either way: garlic and salt first, then the pine nuts, then the basil, and the oil last of all.
Ingredients for four portions of pasta
- 60 g fresh basil leaves
- 1 clove of garlic
- 1 tsp coarse sea salt
- 30 g pine nuts
- 40 g grated parmesan and 20 g grated pecorino
- 120 ml mild extra virgin olive oil
- 400 g linguine, trofie or trenette
Method
- Rinse the basil and dry the leaves completely. Water in the mortar makes the pesto watery.
- Crush the garlic and salt to an even paste. The salt works as an abrasive.
- Add the pine nuts and crush to a coarse paste.
- Add the basil in three batches. Press the pestle against the wall of the mortar and drag it round, rather than striking straight down. The leaves should be rubbed apart.
- Stir in the cheese, and work in the olive oil in a thin stream until you have a thick, glossy cream.
- Cook the pasta. Set aside two decilitres of the cooking water before you drain it.
- Turn the pasta and pesto together in a bowl off the heat, and loosen with cooking water until the sauce is supple. Pesto should never be heated in a pan. The cheese splits and the basil loses its freshness.
The classic way to serve it
In Liguria, diced potato and green beans are cooked in the same pot as the pasta, and everything is turned through the pesto at the end. The potato starch binds the sauce and makes the dish rounder.
Frequently asked questions
How do you use pesto in pasta?
Never in a hot pan. Turn the pasta and pesto together in a bowl and loosen with the pasta cooking water until the consistency is supple. The cooking water contains starch that binds the oil and cheese together.
How long does home-made pesto keep in the fridge?
Three to four days in a sealed jar with a layer of olive oil on top. The layer of oil shuts out the air and keeps the colour green. Pesto can also be frozen in an ice cube tray.
How is pesto eaten?
Mostly on pasta, but also spread on grilled bread, stirred through potato salad, or as a spoonful in vegetable soup just before serving.
What is the difference between green and red pesto?
Green pesto is basil from Liguria. Red pesto comes from Sicily, where tomato and almonds replace much of the basil and pine nuts.
Can I swap out the pine nuts?
Yes. Walnuts and cashews give a milder and slightly sweeter pesto. The technique is the same.
Where to find the ingredients
Pine nuts and other nuts and seeds are the foundation, and you need good quality grated Italian cheese. Choose a mild olive oil, because a robust Tuscan oil takes over the flavour. You will find the pasta under pasta, and ready-made pesto in jars among the pasta sauces. See also the recipe for pasta carbonara.
