Is Pesto Spicy?

Short answer
Although raw garlic, basil, and some olive oils can sometimes be described as "spicy," traditional basil pesto is not a spicy sauce in the same way that chilli-based sauces like chimichurri, harissa, or gochujang are.

Long answer
There are so many different styles of pesto available that drawing too many generalisations is something of a mug's game. Major brands like Sacla, Filippo Berio and Belazu have at least one spicy pesto in their portfolio of sauces, but the inclusion of chilli peppers is in no way traditional and does not feature in classic basil pesto.

Pesto is a proudly pungent sauce thanks to the inclusion of seven big, bold flavours: basil, olive oil, garlic, Parmigiano-Reggiano, pecorino, pine nuts, and salt. This pungency can occasionally be mistaken for spice or the kind of heat you get from chillies, but an expertly made pesto will have a harmony of flavours with no single ingredient dominating the others.

While the salt and cheese run no risk of making your pesto taste spicy, the basil, olive oil, pine nuts and garlic could be guilty. Let's look at them one by one.

Basil
In the same way that coriander tastes soapy to some people, basil tastes spicy to others. Occasionally it's because people have used the wrong variety of basil (Thai basil is known for its spicy, liquorice flavour and is completely different to sweet Italian basil) but usually it's just down to people's own particular tastebuds.

Olive oil
Just like wine, olive oil varies greatly in its aroma, taste, colour and complexity. There's a myriad of words to describe their different characteristics, although the most commonly used descriptors are fruity, buttery, peppery, grassy, and spicy. The official pesto recipe calls for Ligurian olive oil, which is slightly fruity and lacking in any bitter or spicy notes. However, if you choose a different variety you could be getting into the bitter or spicy territory. (One other thing to note is that olive oil that is old or hasn't been stored properly can become rancid, which can be mistaken for spiciness.)

Garlic
We're a bit wimpish when it comes to raw garlic. If you use just a tiny bit too much, you're in danger of your pesto tasting unpleasantly spicy. You could simply reduce the amount of garlic you use, but we prefer to roast the cloves before including them to ensure that we can still enjoy a robust garlicky taste but without the spiciness which is a hallmark of raw garlic.

Another important consideration is how you process your garlic cloves. Chopping them with a knife will give you the least intensity, while grating them with a very fine grater will result in a garlicky taste so strong that you'll think you've been assaulted.

Pine nuts
Pine nuts aren't spicy, although cheaper varieties, especially from China, can leave a metallic aftertaste in some people's mouths which can often be confused with spiciness.