Can I use leftover coffee instead of water when making a new pot?

by Ben
(Calgary AB)


Is it OK if I decide to use the leftover coffee to brew a new pot of coffee? I would have to add some water as well, so the old coffee would be watered down.

Would this be a problem for my coffee maker? Could it do any damage?

Would the new coffee have more caffeine than normal? I'm guessing taste would suffer, but in what ways?



I couldn’t help but smile at your question. 😁

How to make a coffee geek squirm!

I’ve never done what you’re suggesting. But in the summer I’ll sometimes keep leftover coffee in the fridge so I can use it to make iced coffee. (Not to be confused with cold-brew coffee.)

That said, I can’t think of a compelling reason why you shouldn’t “re-brew” some coffee from time to time.

It will make the secondary brew stronger, so long as you use the same amount of coffee as usual. And yes, a bit more caffeine.

Mess with the taste? Absolutely! If I were doing this, I’d only do it with a really ordinary coffee… and never with a really good gourmet coffee.

Will it damage your coffee maker? Probably not, so long as it’s just the coffee you’re re-brewing, and not with milk and or sugar!

One note of caution. It could become a bit of a health hazard over time.

When your brewer completes a cycle, there is still water left in the system, particularly in the pump.

If you’re re-brewing coffee, that means some coffee will be left sitting in the brewer for the next 24 hours at least. And guess what loves a warm, wet and dark environment? Bacteria! And yes, bacteria are happy to grow in coffee.

So… if you want to re-brew, maybe do it every other day. On the other days, use plain water to flush out the system and keep it clean.

That said… as a coffee lover… I never have and never would re-brew old coffee for myself. 🙂

Thanks for the unusual question!


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