Even if it tastes the same there is nothing appetizing about brown oxidized pesto. I used to find it so annoying when I would go to all the trouble and time to make a fresh batch of pesto and within minutes it would go from bright green to muddy brown. Bleh. But now thanks to Maria Rodale's cookbook, Scratch, I finally learned the trick to keep pesto bright green: blanch the basil leaves. So simple! Below is my version of her recipe -- it doesn't have cheese (not that I'm opposed, I just like it better sprinkled on top not mixed in), uses walnuts instead of pine nuts, and less olive oil. The amount below will make enough pesto for a full pound of pasta.
During the harvest season I make as much pesto as possible and freeze in small 4oz. little jars. I used to freeze batches of pesto an ice cube tray, but I found that unless I wrapped each little cube in plastic wrap, they would freezer burn way too quickly. So now I just put in a little jar with a layer of parchment paper cut to size over the pesto and freeze.
Boil a small saucepan of water. While water is boiling, fill a big bowl with cold water and add a handful of ice cubes. Place next to your sink. And then place a colander in your sink. Having everything set up prior is super important because you will need to move quickly after you blanch the basil.
When water comes to a boil, add your basil and submerge and stir for no more than 10 seconds making sure all of the basil leaves are fully under water. Remove quickly from the heat and pour water and basil into a colander. Scoop up the wilted basil and add directly to the ice water in your bowl.
Once the basil has cooled down in the ice water bath, drain again into the colander. Using your hands, scoop up the cool, wilted basil and squeeze out any excess water.
Using a food processor, combine the basil, walnuts, garlic, lemon juice and salt. Pulse a few times to quickly chop. With the food processor running, slowly add olive oil to achieve desired consistency. On occasion, I have added a tablespoon of water if I want the pesto a little looser in consistency. I find that adding more olive oil mutes the taste of the basil.