Does 2- day old coffee still have caffeine?

Yes, 2-day-old coffee still has caffeine, but the amount will be less than fresh coffee.

Here's why:

* Caffeine is stable: Caffeine doesn't readily degrade or break down in the coffee.

* Evaporation: Over time, some of the water in the coffee evaporates, concentrating the caffeine slightly.

* Oxidation: Exposure to air can cause some oxidation, which might reduce caffeine content a bit.

How much caffeine is left?

The exact amount of caffeine remaining is difficult to say without knowing the original coffee strength and brewing method. However, it's safe to assume that 2-day-old coffee will still have a significant amount of caffeine, although perhaps a bit less than freshly brewed.

Important Note: Taste and freshness are the main concerns with older coffee. The flavor deteriorates quickly, becoming stale and bitter.