How quickly does pesto lost flavor when kept cold but exposed to air?

I work at a supermarket chain deli, which has some unique food preservation needs not answered by the information I have been able to find, which mostly assumes people are storing food in their home fridge or freezer. We keep a 1/9-size food pan (sometimes shallow, sometimes deep) exposed to the air in the sandwich bar (kept below 40°F/4°C) filled with Armanino pesto, which omits pine nuts, a common food allergen. At the rate we use it, it would take up to a week to use up what's in the food pan. However, we daily top it up with fresh pesto.

I've tried researching how long pesto (without pine nuts) lasts. The information available talks about sealed containers stored in a fridge, not open containers stored in a sandwich bar (which is loosely covered over night). I've followed my food-preservation instincts and suggested keeping less pesto out and storing it in an air-tight container, but have been told it's no big deal. I know that basil is an herb that loses its flavor relatively quickly, but I can't find any information on the details.

Does basil in pesto lose its freshness mainly due to exposure to the air, or is it just a factor of time, unaffected by oxidation? How long can I expect pesto to keep fresh in deli sandwich bar storage conditions?

Best Answer

Never mind flavor -- what you are doing at work is lethally dangerous.

As a blend of garlic, herbs, and oil, pesto is a great incubator for botulism. While keeping it cold retards botulism, your practice of "topping it off" means that there's at least some pesto in the pan that is months or even years old, and how certain are you that the entire pan is 40F and not warmer? Even if it is, listeria is happy to grow at fridge temperature.

Sources recommend storing pesto in the fridge for between three days and seven days. So at the least, you should be throwing it out and cleaning the pan every week.