It’s pretty easy to make homemade pesto—and it tastes twice as good as the stuff from the grocery store. But much like guac, it oxidizes, or turns brown, quickly when it’s exposed to air. So if you don’t use it the second you make it, how do you keep pesto looking fresh and green? Try this quick trick.
What you do: Before you throw basil (or your leaf of choice) into the food processor, blanch and shock it. That is, throw the greens in a large pot of salted boiling water for about 15 seconds until they wilt, and then plunge them into a bowl of ice water and pat dry.
Here’s why it works: Scalding your greens first stops the enzyme action that turns them brown. It actually turns them brighter by making the chlorophyll more visible. Cook them too long, and they’ll become dull again as the chlorophyll leaches out into the water. Plunging them into cold water halts them from overcooking.
The result: In a side-by-side test, our blanched pesto remained bright green a week and a half after we made it, while the un-blanched stuff turned brown the next day. What’s more, when we froze a batch of each, the blanched one never turned brownish. If that’s not magic, well, it’s probably science.