Glass or plastic

Oil over a long shelf life

A nut butter sits against its container for months and it is mostly fat. Over that length of time the question is whether anything moves between the product and the container, and glass settles it by being inert. That is the same argument the oils property makes and it applies here with extra force because the contact time is longer.

Oxygen barrier

The main failure mode is oxidation, and materials differ in how much oxygen they let through over a year. On a product whose shelf life is set by that reaction, the barrier is part of the shelf life rather than a detail of the packaging.

Expectation is real

This category is bought in glass, and a premium product in a plastic jar reads as a cheaper product to most buyers whether or not that is fair. That is worth knowing as a commercial fact rather than arguing with.

What glass costs

Weight and breakage, and a nut butter is dense. A case of filled jars is heavy enough that freight is a line item rather than a rounding error, and breakage costs twice because of what it does to the rest of the case. Neither changes the answer for a retail product.

Where plastic genuinely answers

Food service, bulk formats and anything shipped individually to consumers, where a dropped jar is a routine event and the container is never displayed. That is a different line rather than a cheaper version of the retail one, and it is not what this shelf is for.

References