Pesto is, on the surface, a very simple sauce. It requires no cooking and has few ingredients. And yet, read just about any authoritative source on pesto, and you're confronted with a laundry list of dos and don'ts.
To explore these rules of pesto-making, I've been running recipe tests all week long, and in the process, I've realized an important thing: It's really easy to get sick of pesto. Now, don't get me wrong, because I love pesto, and I get excited for it when summer rolls around and basil crops up at the farmers market. But man, if I'm to be completely honest, I tire of it.
That’s because, for all its simplicity, pesto is a pungent sauce. Don't believe me? Just think of what's packed into it: heaps of fresh, aromatic basil (an assertive herb all by itself); raw garlic; aged cheeses; and rich nuts, plus a good glug of spicy olive oil to hold it all together. There's nothing mild about it. I make this point for a reason: because it helps in understanding what the secrets are to a good pesto.
What I've come to realize is that the best pesto leans toward milder, sweeter, rounder flavors, but even if you don't achieve that goal, it's still really hard to mess it up—because all those flavors, even at their mildest, are still plenty strong. The good news is that this means you actually have a wider margin of error than most experts will admit.
Still, we want the best pesto, right? So how do we get there? Let's take a closer look.
What Is Pesto Sauce?
This may sound like a stupid question—of course we know what pesto sauce is. It's that green, herbal stuff, with nuts and basil and olive oil. But that's not quite right.
Pesto is a more generic Italian term that describes a wide variety of puréed sauces, traditionally made using a mortar and pestle. The most famous, and the one we're talking about here, is pesto alla genovese, from the Ligurian city of Genoa and its environs. While people get creative with it today, using different herbs and nuts and who knows what else, traditional pesto alla genovese contains only these ingredients: basil, olive oil, nuts (usually pine nuts), cheese, and salt. That's it.
There are other pesto sauces worth knowing about, though, including Sicily’s blushing-red pesto alla trapanese, which is rich with tomatoes; southern France's pistou (a version without nuts); and many, many more.
The Pesto Pantheon
Despite its simplicity, there are several variables to explore when making pesto alla genovese. Read those who are dogmatic about proper pesto, and you'll usually encounter the following criteria around the ingredients and process:
- First, there's the basil itself. If you do it the most traditional way, that basil should be freshly picked from the Ligurian hillsides, when the leaves are small and the basil plants are flowering. Obviously, that's out of the question for most of us.
- Next, there's the olive oil, which should be buttery and mild, freshly pressed from Ligurian Taggiasca olives. Most of us can find this oil, but it tends to be expensive.
- Then there's the cheese: Parmigiano-Reggiano and/or pecorino fiore sardo, and preferably not the sharper, saltier, and tangier (and much more widely available) Pecorino Romano that many recipes in the United States call for.
- The nuts are typically pine nuts, though some recipes will substitute walnuts. Most recipes call for them to be untoasted.
- Last, there's the method: Should you use a mortar and pestle, as tradition dictates, or go the easy route and whip it up in a food processor?
I also found, on an Italian website, some necessary "attitudes" for making pesto:
- A little common sense
- Some elbow grease
I decided to run some taste tests in the SE test kitchen to see which of these rules really matter (and whether that website was right about the attitudes). Care to hazard a guess as to which made the most difference?
The Best Equipment for Making Pesto Sauce: Mortar and Pestle or Food Processor?
If there's one shortcut most people take with pesto sauce, it's using a food processor, which turns a somewhat laborious process into one of the quickest and easiest of sauces to put together.
But just look at the name: pesto. It's related to the Italian verb pestare, which means to crush or mash. A mortar and pestle can crush and mash (look at that word pestle, too!), but a food processor chops and minces. Is this an acceptable shortcut? Two side-by-side batches would reveal all.
For my food processor batch, I used a mini processor, because I was working with a half batch of pesto. I also made sure to stir the olive oil in at the end, since blending olive oil at high speeds can sometimes give it bitter flavors, which seemed like an unfair way to disadvantage the food processor batch in this test.
I started by blitzing the garlic and pine nuts together.
Then I added the basil and pulsed it until it was finely minced.
I added the olive oil in a thin stream, stirring it in.
Next, I made the same recipe, using the exact same ratio, with the mortar and pestle.
I started by pounding the garlic into a rough paste.
Then I added the pine nuts, smacking them down into crumbled bits before grinding them with the garlic into a sticky beige paste.
After that, I added the basil in handfuls, crushing the leaves against the side of the mortar until they were reduced to little bits before adding the next handful. Small pinches of coarse sea salt are helpful here, acting as an abrasive that helps break down the basil.
Working the basil into a paste is the most laborious part of the job, and the best way to do it is to both lightly bash at it with the pestle and also use a circular motion to grind it to bits.
Your goal is to form a creamy paste. I found through experimentation that if you wash the basil leaves just before and leave the water clinging to them, it helps to build up this creamy emulsion.
Finally, the cheese gets worked in, followed by the olive oil. It's best to add the olive oil in small increments, working it in with the pestle to maintain that creamy emulsion before adding the next handful.
Eventually, you end up with a beautiful light-green paste that's creamy, almost like guacamole.
The mortar and pestle pesto was looking even better than the food processor one. The proof, though, was in tasting them.
Looking at them side by side, it can be hard at first to see the differences. But the mortar and pestle pesto had pieces of basil of different sizes, and their texture was soft, silken, and tender, totally yielding. The food processor pesto, meanwhile, had lots of uniform little bits, but in the mouth you could feel them all—they felt almost like grit compared with the pieces in the mortar one.
The flavor was different, too. The mortar and pestle pesto was more clearly infused with the flavors of all the ingredients than the food processor one was.
On pasta, the differences really become clear. The mortar and pestle pesto coated the noodles beautifully, bathing them in a gorgeous green-tinted sauce. The food processor pesto just stuck to the pasta in little bits, like glitter, and the oil had absorbed little of the basil's color.
The best pesto, as its name has insisted all along, should be made under the pressure of a pestle.
Does It Matter What Kind of Mortar and Pestle You Use for Pesto?
Since I first wrote this article, I've struggled with a nagging question: Does the mortar and pestle itself matter much? For years, I used a large* ceramic one with a narrow ceramic pestle, and the results were good, but it was a lot of work, and the sauce never fully emulsified the way I wanted it to.
*The large size, I should add, does matter. Most mortars and pestles sold in the United States are very small—useful for grinding spices, and nice as a decorative element to signal to guests that you like to cook—but of limited use for much else. And many of the mortars and pestles sold as "large" are, at best, medium-sized. What you want is a mortar and pestle that can hold at least one quart (one liter), if not two. For most mortar and pestle tasks, bigger is better.
I eventually decided to test it, comparing the large ceramic one I'd always used against two others: a Thai granite mortar and pestle that we've often recommended, and a special Italian set featuring a marble mortar and a large olivewood pestle. The latter is the kind most traditionally used in Italy to make pesto.
Was there a difference? Yes, of course. But what shocked me was the degree of difference. Pitted against the Thai granite set and the Italian one, the shortcomings of my ceramic one were stark. It didn't just not do a good job; it did an unacceptable job.
Chasing the ingredients around the mortar with the narrow ceramic pestle was like playing whack-a-mole, an endless game of chasing stray bits of garlic and pine nuts as they shot around the bowl with each strike. In a way, the long, narrow pestle acted more like a pool cue than a tool designed to crush, deflecting the food just as often as it crushed it.
The Thai granite mortar and pestle did a much better job, and in a pinch it can work. But it still didn't come close to the effectiveness of the Italian marble mortar with the large wooden pestle. That large pestle head was perfect for efficiently smashing the garlic to paste, and the pine nuts, too. The basil yielded under it in a fraction of the time and broke down more fully, the result of excellent shearing forces under the broad wooden pestle head.
(To be clear, in other tests, I found that the Thai granite mortar and pestle was better than the Italian one for making a Thai curry paste, which contains much tougher and more fibrous ingredients; the granite pestle did a much better job of pulverizing those compared with the wooden one. Perhaps unsurprisingly, these tools are optimized for the foods they are intended to make in their countries of origin.)
If you want to make the very best pesto, get yourself a mortar and pestle from the Mediterranean. It's not cheap, but it'll remain in your family for generations, possibly centuries.
Testing Pesto Sauce Ingredients
A Note About the Basil
I omitted one big factor in my tests: the basil. As essential as basil is to Genovese-style pesto, I concluded that most of us have a limited set of options for it. Unless you're reading this from Liguria itself, you probably don't have access to the prized basil of that region.
If you happen to grow your own, lucky you. If you have access to a good farmers market that carries beautiful tufts of fragrant basil at the height of summer, definitely go for it. If you have to settle for supermarket clamshells of hydroponic herb, well, then, that's what it's going to be. And, frankly, some of that stuff isn't bad. Basically, get the best fresh basil you can, and that's all there is to it.
How Much of Each Ingredient Should Go Into Pesto Sauce?
Without a doubt, in a sauce as simple as pesto, the ratio of ingredients is of paramount importance. Because I've made a lot of pesto in my life, and because I’ve consulted dozens of recipes in books and online, I started out with a pretty good general sense of how much of each ingredient to use.
To arrive at what I think is a great ratio of ingredients in my recipe here, I dialed in the quantities during the process of testing the other components, gradually adjusting and tweaking through each successive batch until my colleagues and I agreed that I'd nailed the sweet spot. Still, it's a matter of personal taste, so if you want your pesto with more garlic, or less cheese, just go ahead and adjust it to your own liking.
What Is the Best Olive Oil for Pesto Sauce?
The first test I wanted to do was of the olive oil. I went into this thinking this would be one of the most important factors in the final sauce. Because there are so many thousands of brands of olive oil on the market, there was no way to try all of them, so I kept it simple here to test a basic premise: Does good Ligurian olive oil matter?
To find out, I pitted a bottle of pricey Ligurian oil against a months-old jumbo tin of cheapo, all-purpose olive oil that we use in the test kitchen for everyday tasks. I made two equal batches of pesto, with the only difference being the oil.
Nearly every taster in the office (there were about four or five in most cases, who, I should note, never knew which variable I was testing) preferred the pesto made with the Ligurian oil—just one gravitated to the pesto with the cheaper oil. But, while the Ligurian oil came out on top, being more buttery and rounded in flavor, we all agreed that the differences were incredibly subtle. In fact, few realized the oil was different, and many assumed I had changed the garlic or some other ingredient.
Going back to the pungency of pesto, this makes some sense: When it's loaded with basil, garlic, aged cheeses, and nuts, the nuances of a good oil become much harder to taste. That doesn't mean it makes no difference, but the differences aren't as stark as one might think.
If you use an absolutely awful, rancid oil, or a very, very spicy, aggressive one, those differences will be more apparent. But as long as you're using a decent, somewhat mild olive oil, your pesto is going to be good; if you feel like using an even higher-quality, not-too-spicy oil, whether Ligurian or not, it may be subtly better.
What Cheese Should Be Used in Pesto Sauce?
Historically, the cheeses of true Ligurian pesto were Parmigiano-Reggiano and Pecorino Sardo (or Fiore Sardo), a Sardinian sheep's-milk cheese. When pesto first became popular in the United States, however, Fiore Sardo was pretty much unavailable here, so recipe writers substituted the next best available thing: Pecorino Romano. But Pecorino Romano is saltier, sharper, and tangier than Fiore Sardo.
So my question was: Does it really matter? To test this, I made two batches of pesto. The first had equal parts Parmigiano-Reggiano and Pecorino Fiore Sardo, which tends to be the ratio of those two cheeses called for by most recipes I looked at. In the other, I used Parmigiano-Reggiano and Pecorino Romano, but here I used 50% more of the Parmesan and 50% less of the Pecorino Romano—using more of the Parm and less of the Romano seems to be the solution most recipes recommend to account for Romano's more assertive flavor.
Tasters preferred the batch with Fiore Sardo, with its ever-so-slightly sweeter, fruitier, less harsh flavor. And yet here, too, the differences were very minor. So, once again, if you can find the Fiore Sardo, it will make a marginally better pesto sauce, but Pecorino Romano makes a darned good one, too (and, frankly, Parmigiano-Reggiano alone makes a great one as well).
What Nuts Go Into Pesto Sauce, and Should You Toast Them?
Most recipes for pesto sauce call for pine nuts, but walnuts are not unheard of. In all the recipes I looked at, the pine nuts were tossed directly into the sauce, but I wondered whether there was any benefit to toasting them first, which would enhance their nutty flavor.
Side by side, though, the two batches I made were nearly indistinguishable from each other: Not one taster could tell the difference. Because I had made them and knew what flavor I was looking for, I could faintly detect the roasted-nut flavor in the lingering aftertaste of the sauce, and I honestly didn't think it did the sauce any favors—it detracted from the sweet roundness that makes a good pesto taste good. But if they weren’t looking for it, I'm not sure most people would even notice.
The verdict: Toasting is not worth it.
Should You Add Butter to Pesto Sauce?
In a couple of recipes, including Marcella Hazan's in The Essentials of Classic Italian Cooking, a small amount of butter is worked into the pesto in addition to the olive oil. I made a batch with butter, but no one could figure out if or how it was different. It may marginally help to bind and emulsify the sauce when you toss it with pasta, but it turned out to not be an essential addition.
Because pesto is such a strong sauce, anything you do to reduce its pungency just a little and steer it toward a sweeter, rounder-flavored sauce will help. That includes selecting a good, mild olive oil; using Pecorino Sardo cheese instead of Romano; and not toasting the pine nuts. Not following the rules above won't ruin your pesto, though.
Staying true to tradition and using a mortar and pestle makes a much more noticeable difference. If there isn't a chance in hell that you'd ever use a mortar and pestle, then yes, you can still make pesto in a food processor and it will be fine, but it will be just fine. It won't be special. It won't be magical and beautiful. Because that requires some special attitudes: enthusiasm, common sense, and definitely some elbow grease.
Editor’s Note: This article has been updated since it was originally published to include new insights into the mortar and pestle used, and to revise the technique slightly in light of the improved equipment recommendation.