When blended with pasta, pesto -- a flavorful blend of crushed basil leaves, garlic, olive oil, Parmesan cheese and pine nuts -- derives some of its appeal from the main ingredient's bright green leaves. Bruised or crushed basil leaves turn black quickly, though, so you have to make and serve the pesto almost instantly to present an eye-catching plate. To slow oxidation, blanch the basil leaves, which kills the enzymes that cause oxidation. You also can add an ingredient known to slow oxidation -- like lemon juice or ascorbic acid -- to the pasta water or the pesto.
Pick the basil leaves off the stems. Making pesto with only the leaves results in a smoother, better-tasting pesto. Bring a pot of water to a boil; then, fill a bowl with cold water and ice to make an ice bath.
Drop the basil leaves in the boiling water for no longer than 5 seconds. Quickly lower the strainer into the pot and fish out the leaves. You can also use tongs to remove the basil from the boiling water.
Submerge the blanched basil leaves in the ice bath until they're cold so the heat won't cook the delicate leaves. Remove the basil leaves from the ice bath and dry them before making your pesto.
Boil the pasta in a blend of water and lemon juice. "New York Times" food writer Harold McGee suggests using 1/4 cup of lemon juice for every quart of water. You also can add a heaping tablespoon of cream of tartar for every quart of water you use to boil the pasta, which also slows basil oxidation.
Pulverize a vitamin C tablet in a mortar and pestle and add it to the pesto. The vitamin C tablet is made from ascorbic acid, and adding it is one of the simplest methods to keep pesto from oxidizing. While vitamin C tablets are tart, robust flavors like garlic and Parmesan cheese mask the taste.
Drizzle a small amount of rice vinegar in the pesto. Like lemon juice, rice vinegar slows oxidation but has a less noticeable flavor than some vinegar types such as balsamic. Use rice vinegar sparingly, though, so as not to interfere with the pesto's flavor.
- Freeze leftover pesto in an airtight container or a resealable freezer bag for up to three months.