Is Pesto Kosher?
For people following a kosher diet, traditional Pesto Genovese is not permissible unless every ingredient and process has been kosher-approved. Particular attention should be paid to the content and production method of the cheese.
Judaism splits food into three categories: dairy, meat (including poultry) and pareve (meaning neutral). The latter category essentially covers all foods that are not made from meat, dairy, or any of their derivatives. They come with their own set of rules to ensure that all stages of their processing or production follows kosher guidelines.
Most of the ingredients in traditional Genovese pesto are pareve - olive oil, garlic, basil, salt and pine nuts, so providing kosher guidelines have been followed in their preparation, they can be freely consumed. The complications arise when we cast the spotlight on dairy which is used to make Parmigiano-Reggiano and Pecorino. These hard, Italian cheeses are made from cow's and sheep's milk respectively, and because both 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 which are made with the aid of rennet to split the curd and whey. Many cheesemakers these days use non-animal rennet, but major Italian producers still use rennet made from the stomach lining of a calf. In fact, European Law dictates that Parmigiano-Reggiano must be produced using calf rennet if it is to be granted that name.
Even though calfs are kosher, if the animal was slaughtered without kosher supervision, the whole animal, including its stomach lining, is no longer kosher. This 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 really 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 meat and dairy cannot be consumed 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, the rules are even more strict as chametz foods (anything that consists of grain that has risen or been fermented) cannot be eaten. This means pasta is off the menu, which is relevant purely because pasta is by far the most common pairing for pesto.
It is perfectly possible to make kosher pesto. However, unless every ingredient and process has been kosher-approved, you cannot say with absolute certainty whether it is kosher or not. On that basis, 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 down to personal judgement.
How to make your own kosher pesto
To make kosher pesto at home, simply follow our recipe for the ultimate basil pesto and omit the cheese. (Nutritional yeast is a common 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 will also have to ensure that all the ingredients you source can be traced to producers that follow kosher rules in their production and processing environments.