Is Pesto Kosher?

Short answer
Traditional Pesto Genovese is not permissible for people following a kosher diet unless every ingredient and process has been kosher-approved. You should pay particular attention to the cheese's content and production method.

Long answer
Judaism splits food into three categories: dairy, meat (including poultry), and pareve (meaning neutral). The latter category covers all foods not made from meat, dairy, or their derivatives. They have rules to ensure that all stages of their processing or production follow kosher guidelines.

Most of the ingredients in traditional Genovese pesto are pareve: olive oil, garlic, basil, salt, and pine nuts, so as long as the producer has followed kosher guidelines, you can freely consume them. Complications arise when we look at the dairy used to make Parmigiano-Reggiano and Pecorino. These Italian cheeses are made from cow's and sheep's milk, respectively, and because both of these animals are herbivores, chew their cud and have cloven hooves, they are kosher. That, in turn, means their milk is kosher too.

But things get tricky when we look at the production methods of some hard cheeses made with rennet to split the curd and whey. Although some cheesemakers use non-animal rennet, European law dictates that Parmigiano-Reggiano producers must use calf rennet to make their cheeses.

Even though calves are kosher, if abattoirs slaughter them without kosher supervision, the whole animal, including its stomach lining, is no longer kosher. That is when judgement takes over. Some argue that any cheese without full kosher certification can never be considered kosher; others take a more relaxed position. It all depends on whether people choose to follow the rules to the letter or follow the spirit of the rules instead.

It gets even more tricky when you appreciate that kosher rules dictate that anyone following a kosher diet cannot eat meat and dairy together in the same meal (or even prepared using the same utensils). So, strictly speaking, even if you find or make a kosher pesto, you cannot eat it with meat or poultry.

During Passover, people must follow even stricter rules. They must avoid eating chametz foods, which include anything made with leavened or fermented grains. As a result, they exclude pasta from their meals since it's commonly paired with pesto.

In summary
It is perfectly possible to make kosher pesto. However, unless every ingredient and process has been kosher-approved, you cannot say with certainty whether the sauce is kosher or not. It's best to assume that all the pestos you find in UK supermarkets are not kosher. How strict or liberal you feel about the guidelines is purely up to personal judgement.

How to make kosher pesto
To make kosher pesto at home, follow our recipe for the ultimate basil pesto and omit the cheese. Nutritional yeast is a typical cheese substitute as it is naturally vegan and has a pleasing cheesy flavour. However, during Passover, you may find that even this is non-kosher. You must also ensure that you can trace all the ingredients to producers that follow kosher rules in their production and processing environments.