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[Photograph: Shutterstock]

Pesto is among the best-known sauces to come out of Italy, and when most of us think of pesto we think of the Genovese recipe, which boasts several ingredients that are hallmarks of Italian cuisine; sweet basil, hard salty cheeses, olive oil, garlic, and pine nuts.

A consortium of restaurateurs and food producers in Genoa established an "official" recipe for their pesto that calls for young basil leaves to be ground in a mortar and pestle with salt and garlic (one clove for every thirty leaves). Pine nuts, grated Parmesan and Pecorino cheeses, and extra virgin olive oil are added until the desired balance and consistency are achieved.

This pesto genovese is made quickly and served fresh, while its flavors are bright and strong. The pesto is never heated, only warmed through when tossed with fresh-cooked pasta. The Genovese consortium calls this the only true pesto, and insists that it always be made with basil grown in the region.

Yet pesto is familiar in homes far beyond the port city of Genoa and the coastal towns of Liguria, and jars of green pesto are a familiar sight on supermarket shelves. The good burghers of Genoa may look down their noses at these other pestos, but the popularity of their sauce has made it one of the city's greatest exports since a fellow named Christopher Columbus.

The first recorded recipe for Genovese pesto comes from a late 19th century cookery book, La Cuciniera Genovese, by Giovanni Battista Ratto. The recipe was not one that would satisfy purists today—Ratto suggested using a little butter in addition to olive oil; marjoram or parsley if one couldn't get basil; and Dutch cheese mixed in with the Parmesan—yet all the essential elements of modern Genovese pesto were present.

Before Ratto's pesto, there were other Italian sauces and spreads, dating back as far as Roman times, with broadly similar ingredients, such as moretum, made with garlic and cheese, and agliata, made with garlic and nuts. The missing ingredient in all this was basil, which is not actually native to Italy. Alexander the Great is credited with first bringing the herb west from Asia. Centuries later it would find a new home in rich Ligurian soil and became one of the definitive flavors in Italian cooking.

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[Photograph: Josh Bousel]

Pesto genovese is not the only authentic Italian pesto. Pesto rosso is made with sun-dried tomatoes and almonds, while versions from Southern Italy favor sweet red peppers or cherry tomatoes. (If you want to experiment with your own pesto variations, we can show you how!) What all traditional pestos have in common, and what defines a pesto as a pesto is that the ingredients are crushed with a mortar and pestle.

The mortar and pestle are so essential that it's right there in the name: "pesto" comes from the same root word for "pound" as "pestle." Crushing ingredients like basil leaves yields maximum flavor and gives sauce a pleasingly uneven texture. Using a mortar and pestle also creates a more stable emulsion between the crushed ingredients and the olive oil. When making pesto genovese, some cooks choose to quickly blanch and shock basil by plunging it in boiling water and then ice water, to deactivate the enzymes in the leaf so that the pesto holds its bright green color.

Of course, there isn't a mortar or pestle big enough to generate the amounts of pesto sold through supermarkets. Pesto in a jar is typically made by an industrial-scale mechanical processor, and low-grade basil is often used because the process won't retain any of the delicacy of the herb. The product is stabilized for the shelf with oil, salt, and acid, resulting in a less fragrant pesto with a uniform texture.

Commercial pesto often contains ingredients that even Giovanni Battista Ratto never allowed for— cashew nuts are commonly used instead of or in addition to pine nuts, no doubt because pine nuts are more expensive. (One popular brand I came across didn't contain any nuts or seeds at all.) Many brands use Italian-style cheeses such as generic parmesan or romano. If the label names Grana Padano, Parmigiano-Reggiano, or Pecorino Romano as ingredients, those are protected designations that may suggest a quality product, while words like "traditional," "classic," or "Genovese" on a label are no guarantee of quality.

A jar of pesto should be stored in the refrigerator after opening and lasts for two to three weeks, but it may start to lose flavor from the moment you open the jar. If you can find it, frozen pesto offers the closest commercial approximation of home-made pesto's freshness, because freezing halts the deterioration of the highly volatile aromatics, particularly basil, that give pesto much of its vibrancy.

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[Photograph: Bill SFNMl]

The popularity of commercial pesto genovese has led to the arrival of other jarred pesto variations on supermarket shelves, with sun-dried tomato pesto that mimics pesto rosso perhaps the most ubiquitous in the U.S. (It may or may not contain almonds.) Other pesto sauces use parsley or spinach in place of basil, hot peppers or eggplants, or ricotta cheese in lieu of hard cheese.

Whatever the ingredients, pesto is primarily thought of as a pasta sauce. In its native Liguria, it's traditionally paired with little twists of dense noodle called trofie, or long flat noodles called trenette, and served with green beans and potatoes that are boiled in the same water as the noodles. Ligurians also use pesto as a flavor booster for minestrone soup, so you could take that as an endorsement for using pesto as a condiment. (The French do the same thing with their version of pesto, pistou, which is broadly the same but without the pine nuts.)

Pesto in vinaigrette makes for a fresh and lively salad. Pesto can also be used in place of a tomato sauce in recipes for lasagna or pizza, or as a perfect complement to the subtle flavors of chicken, potato, or white fish. Try it baked on cod, mixed with mayo in a chicken sandwich, or tossed into a potato salad, and it's like springtime on your palette. We can't all be lucky enough to live on the Italian coast. A little taste of Genoa in a jar might be as close as many of us get.

About the author: Andrew Wheeler is a freelance writer born in England and based in Toronto. You can find him on Twitter @Wheeler.

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