Despite our shared inclination to overlook the expiry date of pantry items, the reality for some of these foodstuffs, like peanut butter, is that they do go bad. This is largely due to their high fat content, which is part of what makes them so appealing in taste. The fat in peanut butter, unfortunately, will eventually turn, going rancid after a period of time. However, this process takes a considerable while. As per the guidelines set forth by the U.S. Department of Agriculture (USDA), a sealed store-bought jar of peanut butter may stay consumable for a span of six to nine months on your pantry shelf, and an opened one is safe for approximately two to three months. Additionally, these durations are endorsed by the National Peanut Butter Board.

Differently, natural peanut butter doesn't last as long because it lacks preservatives and stabilizers. The shelf life of natural peanut butter is cut short by three months compared to its commercial counterpart. Hence, storing it in the refrigerator-even before opening-can extend its shelf life to about three to four months.

Before eating, it's advised to conduct a sniff test. Rancid peanut butter often carries a metallic scent. It might also appear darker and show texture alterations, like difficulty in spreading, cracks, or hardness. If any of these indications arise, whether it's commercial or natural peanut butter, it's best to opt for a fresh jar.

However, don't be alarmed if you see oil separation, especially in natural peanut butter. This doesn’t signify spoilage as natural variants don't contain added stabilizers, leading to occasional oil separation. Quick stirring should help mix the oil back in and the peanut butter is good to use.

Well-known commercial peanut butter brands like Jif or Skippy are suited for pantry storage due to their ability to withstand varying conditions, including indirect sunlight and mild temperatures. Natural peanut butter can be stored in the pantry as well. However, to prolong its shelf life, especially once opened, it's recommended to keep it in the refrigerator instead.