I know caffeine doesn’t evaporate from coffee in its liquid state, but what about coffee grounds left out in the open? (I use that as a form of de-odorizing the house sometimes.)
I’m getting a headache/lightheadedness from leaving a lot of coffee out to air its smell in the house, and I’m wondering if it’s caffeine vapor.
Caffeine is a solid. It doesn’t evaporate.
Being a solid doesn’t mean something can’t evaporate, although the word is different, we call it sublimate; CO and Iodine are two examples of substances which sublimate visibly (in the case of Iodine, the vapors themselves are visible; for CO(s), what forms the mist is water from the air condensing on the cold just-released CO(g)). But in the case of caffeine no, it doesn’t have a noticeable vapor pressure. Whatever it is, it’s a different substance.
Coffee is full of volatiles. That’s why it should be stored in sealed containers, and why it’s got limited shelf life. But as already explained the caffeine isn’t one of them. It does have a flavour and contribute to coffee taste, but obviously isn’t the main player, or no one would drink decaffeinated.
I stored a ziploc bag of cookies next to a bag of coffee for a week. The cookies ended up tasting “burnt” from the amount of coffee that managed to seep out of the coffee bag and into the (sealed!) bag of cookies. Yes, ziploc bags can have things diffuse through them given enough time and a high enough concentration. I’m sure most of the pantry was covered with the coffee smell, but most things were in cans, which are far less permeable than ziploc bags.
I actually found out about the permeability of ziploc bags after making kielbasa and putting it in a freezer with a carton of ice cream. The cardboard ice cream container is also permeable somewhat, and I ended up with garlic flavored ice cream.