Does coffee that's been sitting around in the pot all day have less caffeine than freshly brewed coffee?

June 3, 2012 3:42 PM

Does coffee that's been sitting around in the pot all day have less caffeine than freshly brewed coffee?

If not, what factors affect the caffeine level of older coffee? Does refrigeration make a difference? Does a thermal carafe?

NOTE: This question is NOT in reference to whether coffee that's been sitting around all day tastes good, only whether the caffeine content is the same.

posted by Caviar to food & drink (12 answers total)

Coffee detective says the caffeine level remains the same or might increase as a percentage of the liquid because some water might evaporate.
posted by jessamyn at 3:54 PM on June 3, 2012

But that's really only discussion of whether it evaporates, not whether it breaks down. I ask because older coffee seems to have much less kick to it.
posted by Caviar at 4:20 PM on June 3, 2012

From Jessamyn's link:

To answer your first question, caffeine does not evaporate or otherwise disappear after brewing. There will be as much caffeine in your coffee after five hours as there is after five seconds.

How does that not answer the question at hand? The caffeine is not 'breaking down'. It's just sitting there.
posted by trip and a half at 4:40 PM on June 3, 2012

Ah okay then you might want this answer from the Stack Exchange cooking site

According to Sigma-Aldrich, pure caffeine has a shelf-life of four years at room temperature, or many years at 2-8°C.

A caffeine solution can be stable for months even at moderately high temperatures.

So, essentially, your day old coffee has still all its caffeine in it, although probably it does not taste that well, but that's caffeine unrelated.

As a side note, after drinking coffee/tea/Coke/etc. it will take ~1-2 hours for blood caffeine levels to peak. Caffeine half-life in the body is ~3-6 hours.

posted by jessamyn at 4:43 PM on June 3, 2012 [5 favorites]

I have often wondered this; thanks for asking. These links discuss room temp or colder coffee... I wonder if the caffeine remains if you take the room temp coffee and re-heat it?
posted by LobsterMitten at 4:54 PM on June 3, 2012

For example, this says that a pure caffeine solution is shelf stable for 3 days, but no info about whether it may react with any of the hundreds of other chemicals in a brewed cup of coffee.

http://cameochemicals.noaa.gov/chemical/19945

This seems inconclusively tested.
posted by Caviar at 4:56 PM on June 3, 2012

I doubt the other chemicals have a significant effect. They're all from the same source, the coffee bean, and the plant produces caffeine because it's a pesticide. Evolutionary pressures strongly suggest that plants that produce more caffeine that's stable for longer have a better chance of surviving.
posted by sbutler at 5:04 PM on June 3, 2012

Look you have to compare the evidence you have on hand.

On the one hand you have rigorously tested empirical data stating that caffeine in solution is very stable.

On the other hand you have a feeling that old coffee has less kick.

The former evidence outweighs the latter.
posted by kavasa at 5:10 PM on June 3, 2012 [5 favorites]

Caffeine is chemically stable up to the point at which it turns into a gas (which is higher than the boiling point of water). It doesn't react with anything in your cup of coffee.
posted by jessamyn at 5:12 PM on June 3, 2012 [1 favorite]

Old coffee seems to have less of a "kick" only because all the nice feelings you get from drinking a hot and tasty beverage are lacking.

Caffeine is important, but it's far from the only thing in your coffee.
posted by helicomatic at 5:33 PM on June 3, 2012 [4 favorites]

Speaking as an organic chemist, there's nothing in coffee that would give me the slightest concern about it reacting with caffeine, which is as stable a biological molecule as you're likely to run across. The acid is the only thing likely to cause any reaction, and caffeine requires much stronger acids than coffee to do anything. Isolating caffeine is a standard undergrad lab, and if they can't massacre the molecule, no amount of sitting around will.
posted by Dr.Enormous at 6:41 PM on June 3, 2012 [12 favorites]

On the one hand you have rigorously tested empirical data stating that caffeine in solution is very stable.

On the other hand you have a feeling that old coffee has less kick.

The former evidence outweighs the latter.

You're incorrect. The placebo effect, your expectation of what will happen when you drink a cup, certainly has a bearing on how you react to an old cup of coffee. If all we are concerned about is the caffeine in the cup, then the empirical data is paramount. If we're concerned with the reaction to the coffee, there are many things beyond the amount of caffeine that affect that.
posted by OmieWise at 5:22 AM on June 4, 2012