From M, 10 April 2011, Pesto – heat before serving?
Q: I have an enourmous over supply of basil in the garden, and am planning to make pesto. Do you heat up the pesto before adding it to your pasta?
A: Thanks for your question. This may be the shortest response I’ve ever been able to give.
No. Never heat the pesto before adding it to pasta. First, the heat will cook the basil, destroying its aroma. Second, if you use cheese (i.e., Parmigiano-Reggiano), it will clump. And third, the heat from the pasta as you toss it with the cool pesto warms it enough to release the aroma of basil, but not enough to destroy it.
Pesto freezes pretty well (although it has enough oil that it doesn’t freeze solid), so if you wind up with more pesto than you can use in a couple of days, freeze it in small containers, the surface covered with a layer of olive oil.