Every year, my family makes peanut brittle using an old family recipe (example recipe, slightly different from ours in quantities). A large portion of this recipe is Karo brand light corn syrup. The brittle is very popular with friends and family because of its foamy, crunchy texture. We achieve this texture by adding a bunch of baking soda at peak temperature, watching the brittle foam up, and dumping it on a tray to cool while it's still really foamy.
This year, we've made two batches, one using a bottle of corn syrup left over from last year, and one using a new bottle we just bought. And there's a difference. The one with the old bottle was properly foamy and held its air bubbles while hardening. The one from the new bottle foamed up, and then went flat before hardening, losing all its air and spreading out more than it usually does.
We'd assume that we made a mistake in our cooking process, except that my mother-in-law, using the exact same family recipe, had the exact same experience. Last year's syrup worked; this year's didn't.
This makes me conclude that something changed about Karo Light Corn Syrup. Maybe the moisture content, maybe the sugar chemistry, maybe something else. There's no published news, and Karo has not responded to our requests for information.
Does anyone know what might have changed about the syrup this year, preferably with citations?
If there are no citations, does anyone have a method by which we could determine how the syrup changed that doesn't require a full chemistry lab?
To forstall questions: no, we don't have both bottles. Also, we cook the sugar+corn syrup to dark amber.
Answering one more question: it was the exact same box of baking soda. And we're talking about batches less than a week apart. Further, my mother-in-law has had the same experience, so we've reproduced the change in behavior in two different kitchens. Absolutely every other variable is accounted for other than the change in corn syrup years.
Update: one more A/B test: we found a bottle of 3-year-old Karo, did a batch of peanut brittle, and it turned out fine.