Is Pesto Gluten Free?

Short answer
Yes, traditional pesto is naturally gluten-free, but always read the label and check that the sauce does not contain wheat, spelt, or barley, all of which contain high levels of gluten.

Long answer
There is absolutely no reason why a pesto should contain gluten, and we're yet to identify any that do.

Some manufacturers of ambient pesto add a little tapioca starch to their sauces (which is naturally gluten-free) to help prevent any moisture from the herbs splitting the sauce over time. We’ve seen other producers add potato flakes, bamboo fibres, nut flour, and all kinds of other thickeners to their recipes, but all these ingredients are also free from gluten.

The only time we advise erring on the side of caution is if you see just the word “flour” (without specifying what type of flour it is) on the label. The worst-case scenario is that it could be wheat flour (one of the primary sources of gluten). However, it’s unlikely to be used in any great quantity, certainly no more than around 1.5% of the sauces’ total weight.

Therefore, in a single serving of pesto (around 50g per person), you would only be consuming 0.75g of flour, which equates to around 0.1g of pure gluten.

The only other reason gluten could be present in pesto is due to cross-contamination, but the chances of that are strikingly low, and there is nothing practical you can do to mitigate that anyway.