How long is the life of a shot of espresso?

This barista says no, you can enjoy your shot for a little while:

In reality, there are only a couple of things that happen to espresso over the course of a few minutes. First, the crema or foam that sits on top of the espresso reintegrates with the liquid. Crema, on its own, contains some of the best flavors and aromatic qualities of the espresso in high concentrations. Drinking it straight can be overwhelming but, it stands to reason, that having the crema reintegrate might actually be a good thing. Second, the espresso cools down. The temperature of espresso has a lot to do with how we taste the various flavors contained within it...

I am not an espresso fan myself--I like regular coffee, but not after it has cooled down, and never reheated. Many folks are perfectly content to microwave a cold cup and drink it.

I imagine that older, colder espresso is palatable to you to the extent that you are willing to tolerate it. A small shot of coffee--and lets face it, that is all espresso is, even if it is brewed in a fancy manner--is going to cool off much more rapidly than a full cup, or a full pot.

Shots die after only ten seconds of sitting. You can tell by the change in color. It goes from a nice pretty brown body with a layer of crema on top to a very dark brown/black color. If you have ever done the taste test and tasted both the dead shot and the good shot, especially if you're sensitive to bitter taste, you can absolutely tell the difference. That is why Starbucks stresses a barista not to allow your shot to sit out for longer than those ten seconds.

Barista

As I understand it, all brewing methods are subject to both oxidation and degradation of yummy acids and oils. I was first introduced to the 10-second rule for espresso as a customer at a Starbucks. According to the barista, if the coffee did not touch something (water, milk, syrup) within 10 seconds it would turn bitter and "burnt" tasting. I was highly skeptical of this claim, so the barista felt obliged to prove her point (which is easily testable, if you can stomach wasting a shot). She pulled a shot and immediately dropped in a teaspoon of cold water (so that I could drink it right away), then handed me the shot glass to try. Delicious. Then, she pulled another shot, we counted to 10 together, she added a teaspoon of cold water, and I drank. Bitter and burnt tasting. Not terrible, but nowhere near as complex and tasty as the first shot. The difference was marked. (Incidentally, she claimed that the temperature of the added water was irrelevant to stemming the bittering process.)

I have since tested this at home on my machine, with the same results. (And I've tested adding hot or cold water, both do seem to stem the degradation process, as she claimed.) If you are skeptical -- as you always should be -- test it (at least somewhat systematically) yourself.

Here is a site with more information about oxidation and degradation of acids and such:

• https://scienceandfooducla.wordpress.com/2014/08/19/coffee-brewing-chemistry-hot-brew-and-cold-brew/

I suspect that an email to the author could easily shed more light on the how and the why.

Espresso starts losing some of its flavour immediately so I'd say drink it within one minute. If made at the right temperature it should be cool enough to drink after a few seconds anyway and after a minute it will start getting too cold to enjoy. I'd also suggest stirring your espresso before drinking to mix the different layers and get a more homogenous drink.

For me, it is not bitterness or flavor, but temperature. When a shot gets cold, it is not good. So, I would say it could last a couple of minutes, but it is not a sipping drink anyhow. Pull it and drink it.

This is correct that coffee flavour alters depended on temperature. However this argument of better is hard to say as its a matter of preference.

For coffee tastings you should try the coffee had a range of temperatures as the flavours alter you may taste something different.