Should Pesto be Made in a Food Processor or Pestle and Mortar?

Short answer
While large-batch producers have no option other than to use machinery, if you're making pesto at home, it will taste infinitely better if you use a pestle and mortar.

Long answer
We’ve done dozens of blind taste tests to find out whether pesto tastes better when it's made with a food processor or with a pestle and mortar. Every single time, the latter option won, and there are three very simple reasons why.

Heat is the enemy of pesto
Electric kitchen appliances generate heat, and the one thing you really don’t want to do to pesto is heat it too much. If you do, all those wonderful fresh herby flavours will be destroyed, or at least dulled down.

Crushing releases more flavour
Food processors and blenders use a very crude way of breaking down ingredients. They effectively just slice ingredients into smaller and smaller pieces. A pestle and mortar, on the other hand, crushes the ingredients, releasing much more flavour in the process.

Fast blades turn olive oil bitter
The third reason you should shun a food processor or immersion blender is because the blade action of electric appliances shears olive oil into microscopic droplets. This causes the release of compounds called polyphenols, which will turn your oil, and therefore your whole sauce, bitter. Using a pestle and mortar doesn't do this.

Even if these rational arguments haven’t convinced you to dust off your pestle and mortar, we can guarantee you that your sauce will taste better simply because you’ve made it with your own bare hands.