Basil is delicate. Heat and air darken it, and running a strong olive oil through a blender can bring out its bitterness.
The fix for next time
- Pulse the basil in short bursts, or use a mortar.
- Stir the olive oil and cheese in by hand at the end.
- Use a mild olive oil.
- Toss with the pasta off the heat.
Can I save bitter pesto?
You can soften it with more cheese, a few extra pine nuts, and pasta water when you serve it. A very bitter batch won't fully recover.
Keeping it green
- Press a thin layer of olive oil onto the surface before refrigerating.
- Fill the jar so that there's less air inside.
- Freeze extra in small portions, without the cheese.
