An experiment in pesto

12 August 2012

If you do a Google search for pesto, you’ll find a deep schism regarding how the perfect pesto should be made. On the one side is the purist crowd, which claims that real pesto must be made with the instrument after which it was named: a mortar and pestle. On the other is the modern crowd, who swear up and down that pesto made in a food processor tastes just as good and is much faster to make. Then there are a few rebels who like to make pesto with a knife, usually a mezzaluna, and those people also think that their method of making pesto is the best. For my purposes, I’m going to lump the knife crowd in with the food processor crowd — using the knife is more time consuming, but the end result should be pretty similar since the ingredients are still being cut with a sharp implement rather than smashed with a blunt one.

I have long followed the blunt crowd, making pesto by hand in a mortar and pestle. But I’ve never had pesto made with a blade before. It is not good to dismiss things out of hand without testing them just because some people on the internet say it’s bad, so I devised a small experiment to see if there would be any discernable difference between the two.

Click on the cut following the picture for more about the experiment, as well as a recipe for mortar-and-pestle pesto.

Left: two leaves of basil were mixed with 1.5 tsp of untoasted sesame oil and smashed in a mortar and pesto until the basil was broken into small pieces. The resulting mixture was transferred to a clean shot glass.

Right: two leaves of basil were mixed with 1.5 tsp of untoasted sesame oil and then cut into small pieces with a sharp knife on a cutting board. To better mimic the actions of a food processor, which chops everything in the same medium, care was taken to cut the basil in the sesame oil, so that any aromatic oils released by the basil during cutting would meld with the oil. The resulting mixture was transferred to a clean shot glass.

A second look at the basil-oil mixture prepared with a mortar and pestle. The oil has taken on a distinctly cloudy, greenish tint, heavy enough that the individual pieces of basil leaf are difficult to see through the liquid. Transferring the mixture into the shot glass was also very difficult, as it was very viscous.

A second look at the basil-oil mixture that was prepared with a knife. The oil, which was chosen over the other oils in my pantry for its clarity and relative lack of colour, is still fairly colourless and clear. Individual pieces of cut basil can be discerned very visibly through the oil. Transferring this mixture into the shot glass was much easier than with the first mixture, as the oil in this one flowed easily.

The oil, being made from untoasted sesames, has a very light taste compared to the other oils in my pantry (indeed, it’s what I generally choose as a “flavourless” cooking oil when I need one). I tasted the oil in the two different mixtures, being careful in both cases not to get any chunks of basil with the oil. The oil from the first mixture, made with a mortar and pestle, tasted strongly like basil. The oil from the second mixture tasted very faintly of basil.


Mixing pesto with a mortar and pestle causes better release of flavours into the oil that serves as the mixing medium, potentially giving rise to a smoother, better blended pesto on the whole. As the blending of flavours is generally considered to make sauces taste better, pesto made with a mortar and pestle would taste better than pesto made with any sharp implement.

Most people will no doubt continue to make pesto with a food processor, as it is much faster and less tiring than using a mortar and pestle. I propose two ways to make the flavour of pesto made using a bladed implement more like pesto made using a mortar and pestle:

1. Use a dull blade, for example, a dull knife or a dull food processor blade. Even better if it takes multiple passes to cut through something — that will ensure that it gets bruised enough to release more oils.

2. Let the pesto sit for some time before consuming, to encourage the flavours to meld better.

And while I’m at it, I may as well share how I make my own pesto:

Recipe for pesto

2 cups basil, tightly packed
4 cloves garlic
1/3 cup olive oil + 1 tsp
1/3 cup pine nuts
1/2 cup freshly grated parmesan (about 25g, in case your grated parmesan has a vastly different density from mine)
1/2 cup freshly grated pecorino romano
salt and pepper to taste

Lightly toast the pine nuts. They get nuttier if toasted more, but I like them more creamy than nutty.

Put the garlic into the mortar and pestle. Smash it to a pulp.

Add the basil and 1 tbsp of olive oil. Smash that to a pulp, too. This is the most time consuming and tiring part and will probably take about 20 minutes. If your arm gets sore, think of something or someone you really hate. If the mixture gets too dry, add more olive oil, 1 tbsp at a time. Do not add too much olive oil, otherwise the mixture will splash when you bash the pestle into it and you’ll end up looking like you’re covered in green pimples.

At this point, the basil should be thoroughly mashed. There should be no large pieces. Add the salt and pepper, keeping in mind not to oversalt because you’ll later add salty cheese. About 1/4 tsp of salt is enough for me. I guess you could just add the salt after the cheese, but for some reason I always add it here.

Add pine nuts. Rejoice at how much easier they are to grind than the basil.

Add cheese and what remains of the 1/3 cup of olive oil. Make sure that everything is thoroughly mixed.

Use immediately, or transfer to a jar. Pour the 1 tsp of olive oil on top of the pesto to minimize contact with the air and put into the fridge. It will keep for… oh, I don’t know, a few days. It never lasts longer than that without getting eaten, anyway.


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