Fresh basil pesto is a quick sauce, but the difference between a fragrant green spoonful and a dull, oily paste lies in how you handle the ingredients. Overprocessing can bruise and heat the basil, too much oil can drown the cheese and nuts, and a heavy dose of raw garlic can overwhelm everything else.
You can make a useful everyday pesto in a food processor or with a pestle and mortar. The result is excellent stirred through warm pasta, spread on sandwiches or spooned over cooked vegetables just before serving.
Ingredients for a small jar
For enough pesto to dress roughly four portions of pasta, use 40g fresh basil leaves, 30g pine nuts, 35g finely grated Parmesan-style hard cheese, one small garlic clove and around 75–100ml extra-virgin olive oil.
Add salt to taste and a small squeeze of lemon only if you like the extra acidity. These are adaptable quantities; some classic pestos use more cheese and less oil.
If cooking for vegetarians, check that the hard cheese is made without animal rennet. Traditional Parmigiano Reggiano is not vegetarian, although suitable alternatives exist.
Choose fragrant sound basil
Fresh, firm green leaves give the most attractive colour and flavour. Pick over the bunch and discard yellowed, blackened or slimy leaves.
Wash when necessary and dry thoroughly. Excess water dilutes the sauce and can contribute to splattering if you later add pesto to hot oil.
If using homegrown basil, harvest healthy tips rather than old woody stems. The smaller upper leaves are often especially fragrant.
Prepare the pine nuts
Pine nuts contribute a buttery, gently sweet flavour. Some recipes use them raw; others toast them lightly to develop a nuttier note.
To toast, put them in a dry frying pan over low to medium heat and move them frequently until just golden. They can burn surprisingly fast.
Let the nuts cool before blending with basil. Hot nuts raise the mixture's temperature, which can darken the leaves and reduce the fresh aroma you're trying to preserve.
Grate the cheese finely
Fine cheese mixes more smoothly than large shavings. Use a microplane or fine side of a grater.
Check the cheese's saltiness before seasoning. Some hard cheeses are strongly savoury, so you may need only a small pinch of added salt.
Avoid pre-grated products containing anti-caking ingredients if you're aiming for the smoothest texture. They can still work in everyday pesto, but the result may differ.
Prepare the garlic
Peel one small clove and chop it roughly for a processor, or crush it with a little salt in a mortar.
Raw garlic carries considerable flavour. Start with less than you think you need, particularly if you'll serve the pesto cold.
If garlic is the only thing you can taste, the sauce has lost the balance between basil, cheese, nuts and oil. You can add more basil to correct that, but it's easier to start modestly.
The quick food-processor method
Put basil, cooled pine nuts, garlic and cheese into the processor. Pulse a few times until the pieces are chopped and beginning to combine.
With the motor running briefly or between pulses, add olive oil gradually until the mixture holds together as a sauce. Scrape down the bowl with the machine switched off.
Avoid blending continuously for several minutes. You want small particles held in oil, not a whipped puree that's become warm from the blades.
Making pesto with a pestle and mortar
A mortar takes longer but gives more control over texture. Crush the garlic with a little salt, then work in the pine nuts.
Add basil leaves in batches, bruising and grinding them into a paste. Stir in the cheese and oil towards the end until the texture suits you.
This method is practical for a small batch and lets you stop while there are still recognisable flecks of basil.
Choose the right consistency
For pasta, pesto should be loose enough to coat rather than sit in clumps. For sandwiches, a thicker paste is often easier to spread.
Add oil a tablespoon at a time. You can loosen pasta pesto later with a little warm pasta cooking water instead of adding excessive oil to the jar.
If the mixture is already watery, more cheese or basil may improve its texture. Don't add large amounts of raw flour or other thickeners.
Taste after mixing
Try a small amount on bread or with a little cooked pasta. Tasting directly from a spoonful of concentrated pesto may make the salt and garlic seem stronger than they will in the finished dish.
If it needs brightness, add a little more basil or a small squeeze of lemon. For richness, add a modest amount of cheese or nuts.
Balance is personal. A delicate pesto for fish may be less garlicky than one designed for a strong tomato pasta sauce.
Toss pesto through warm pasta
Cook your pasta according to its packet, reserving a cup of cooking water before draining. Return the pasta to the pan off the heat.
Add a few spoonfuls of pesto and toss with a small splash of the reserved water. The starch helps the sauce cling and distribute evenly.
Avoid frying fresh pesto over fierce heat for several minutes. Its fresh basil flavour is most noticeable when the sauce is mixed through hot food gently rather than cooked hard.
Try variations without losing the idea
Walnuts, almonds or cashews can replace pine nuts when used in a recipe suited to them. They change the flavour and texture, but can make the sauce less expensive.
Rocket or parsley may replace some basil for a greener, pepperier result. Don't call every green puree basil pesto if it contains almost no basil.
For a dairy-free version, use a tested alternative without cheese and adjust seasoning. Nuts, sesame and dairy are common allergens, so check what you're serving to guests.
Why pesto turns dark
Basil can darken when bruised, exposed to air or heated. Quick preparation, limited processing and sensible refrigeration help preserve its colour.
A thin layer of oil over a small refrigerated portion may reduce surface exposure to air, but it is not a way to make homemade pesto shelf-stable. Keep it refrigerated and use promptly.
Brown colour alone isn't a complete food-safety test. Discard pesto with signs of spoilage or unsafe storage.
Important safety warning about herbs in oil
Homemade mixtures of fresh herbs and oil can support dangerous microorganisms if stored incorrectly. Do not keep homemade basil pesto at room temperature for prolonged periods or attempt casual shelf preservation.
The National Center for Home Food Preservation advises refrigeration and very short holding times for fresh herb-and-oil mixtures, or prompt freezing for longer storage. Its warnings about botulism matter even if the mixture tastes normal.
Make small batches, refrigerate promptly and freeze portions you won't use soon. Do not interpret a sealed glass jar as making the mixture safe on a cupboard shelf.
How to freeze portions
Put freshly made pesto into clean freezer-safe containers or small trays and freeze promptly. Choose portions large enough for one pasta meal.
Once firm, transfer to suitable airtight packaging as appropriate, label and keep frozen. The oil may prevent a cube becoming completely rock hard, so handle portions carefully.
Thaw in the fridge or add a frozen portion directly to suitable hot food. Avoid leaving the sauce on the worktop for hours.
What if it tastes bitter?
Some olive oils become more bitter when processed aggressively. Overblended basil stems, burnt nuts or too much garlic may also contribute.
Try pulsing more briefly, using cooled nuts and tasting the olive oil before adding it. A mild oil can be useful if your extra-virgin oil is particularly peppery.
If the sauce is unpleasantly bitter, piling in sugar isn't a great repair. Adjust the ingredients or make a smaller fresh batch.
A practical habit for the summer harvest
When basil grows quickly, pick a small healthy bunch and make only as much pesto as you will use or freeze promptly.
Label freezer portions with their contents, particularly if you've used a nut alternative. That makes it easier to avoid allergens and choose the right sauce for dinner.
Good pesto is not complicated. Fresh basil, restrained garlic, nuts and cheese in sensible proportion, and enough oil to bring them together are all you need.