Let’s cut to the chase. For store-bought, pasteurized eggnog (the stuff in the dairy aisle), your best friend is that little date stamped on the carton: the "sell-by" or "use-by" date. Generally speaking, you’ve got about 7 to 10 days past that printed date if the carton has never been opened and has been kept consistently cold (below 40°F).
But here’s the ironic kicker: that date is often a suggestion, not a magic switch. If you bought it two weeks before Christmas and it says "use by Dec 20," you’re probably fine sipping it on New Year’s Day. However—and this is a big however—do not push it past three weeks after that date unless you have a death wish or a truly iron stomach.
The "Sniff and Swirl" Method
I know, I know—you want a hard rule. But food safety is tricky, and eggnog is a dairy-egg combo that spoils like a diva. Before you even consider drinking it, do the sniff test. Unopened eggnog that’s gone bad will smell sour, like bad yogurt or gone-off milk. If it smells fine but looks chunky, toss it. Chunks mean the emulsion has broken, and that’s bacteria’s invitation to the party.
Another trick? Give it a gentle swirl. Fresh, unopened eggnog should pour like heavy cream—smooth and uniform. If you see any separation that doesn’t mix back in, or if the carton feels bloated (like it’s about to explode), that’s gas from fermentation. Do not drink that. Your toilet will thank you later.
