Let’s say I poured my existing pot of coffee into the reservoir in my coffee maker where I’d ordinarily pour water. Would the resulting pot of coffee
[ul]
[li]Be undrinkable[/li][li]Be indistinguishable from coffee made with water[/li][li]Be awesome (if one likes strong coffee, that is)[/li][li]Blow up my coffee maker[/li][/ul]
?
Thanks!
I believe that is what percolaters do.
Exactly, only more so. So it’ll be worse than percolator coffee.
Boiling coffee produces new molecules. Most of which are not considered tasty by coffee fans.
Unlike many other questions on the SDMB (time travel, going faster than the speed of light, collecting all the sperm in the world in a swimming pool), there is no need to speculate, this is something anybody can try at home and report back after 20 minutes.
Unfortunately, I’m a tea drinker…
However, my guess would be that you get some really strong coffee.
Except I have no desire to risk blowing up my coffee maker. I don’t have $20 to buy another one. 
What about brewing coffee with milk instead of water?
A drip coffee pot doesn’t reach boiling, does it?
I swear we had a name for this in high school- maybe just “double brewing”? Anyway, it’s been done, but I can’t imagine the results are any good unless you are basically looking for liquid no-doze.
Ok so what we need is a system that simply drips the coffee through a second stage of brewing.
I would imagine trimming a filter down so as to have 2 filters each with a standard amount of coffee stacked on top of each other would basically be what the OP is asking for.
Sounds like whatever its going to be its gonna be rocket fuel…if thats good or bad I will leave to the drinker.
I think this would just eventually plug up your coffeemaker.
I vote for “awesome”. I’m brewing my next pot with vodka. 
I know someone who made coffee that way in an office coffee pot. He just stuffed two of those filter donuts into the coffee machine. Everyone loved it (except me, I won’t go near the stuff). Since it was my office and I was paying for the coffee I made them start contributing to the cost if they were going to do that.
You should be able to try it in a French press or similar method (like the pour-over-a-cone-of-coffee method, whatever it’s called.)
What actually happens is that volatile chemicals evaporate, which is why old coffee loses its flavor (saying this because apparently there is a myth that doing so makes it toxic, which is certainly believable if you have tasted it, and why wouldn’t the same toxic substances form when coffee is brewed?).
You’d start to have coffee residue build up in the coffee maker’s tank and hoses/pipes which will eventually lead to really bad tasting coffee and probably an eventually non-functional coffee maker.
Also, doesn’t the water have to be cold for the right convection currents to make it move in the proper direction, or is that just for big percolator urns?
A percolator makes really lousy coffee because it circulates the water over the coffee grounds many times, not because it circulates coffee over the coffee grounds. Roasted coffee beans contain a cocktail of stuff, and a neat way of understanding how to make good coffee is that the process consists of removing the stuff that tastes good, and leaving behind the stuff that tastes bad. Luckily the stuff that tastes bitter is harder to remove, and tends to get left behind. Unless you over-extract. Which is what a percolator does.
The flavour balance is a delicate thing, as Michael63129 notes, there are volatiles that are critical to the flavour balance, and when these are lost the what remains is pretty awful. If you are a fan of espresso you will know that a newly made coffee is blissful, but in two minutes will lose almost all of its allure. The crema atop the coffee contains many volatile aromatics and is critical to the flavour. One trick espresso freaks do is to extract coffee into a set of tiny cups over the period of an extraction, and to taste the different components - the initial drip versus the last taste very different, and none really nice - but combined they can be magnificent.
This is also a clue as to why instant coffee is just not even the same drink as real coffee.
If by “coffee maker” you mean an all on one drip coffee maker, you don’t want to use anything other than water in it. Many have a little steam generating chamber that forces the hot water up and into the filter. When the water runs out this boils dry. Using coffee instead of water will leave a residue of coffee in the chamber which will burn and stick, and eventually kill your machine.
Wait a moment. I jerk off a lot. And fast.
FWIW, consommé (beef, chicken, fish, game) is made precisely by simmering fresh food in the stock produced from that food to begin with.
You could try this with coffee, and we will eagerly await your report.
Measure coffee into pot, add hot water.
Bring mixture to rolling boil.
Reduce heat, cover and simmer for two hours.
Filter out the grounds.
For optional extra flavor:
Measure new coffee into pot with the filtered coffee from above.
Bring mixture to rolling boil again.
Add crushed No-Doz tablet for extra zest, if desired.
Reduce heat, cover and simmer for two more hours.
Filter out the grounds.
Enjoy. :eek:
Apropos, there was a fabulous Garfield strip some years ago. I wish I knew how to search for such things.
1st panel: Jon and Garfield each have a cup of coffee. Each takes a sip.
2nd through 5th panels: By stages, both Jon and Garfield morph into bug-eyed werewolves.
6th panel: Jon says: “Not half bad!” Garfield agrees: “Not half bad at all!”
At best, you will end up with really strong coffee, about as strong as if you just used twice as much coffee grounds. At worst, you will end up with really strong UNDRINKABLE coffee. And in both cases, you’ll need to clean out your coffee maker fairly regularly.
Simpler just to drink espresso.
So why is espresso so strong, oz. to oz.?