Like any food product, the quality goes down hill after the food is prepared. The better coffee shops I go to will brew directly into an air pot then put a timer on the pot. At one hour post brew, it is dumped down the drain and a new pot is made.
I have had coffee last all day in a sealed air pot but there is a marked down hill slide of quality as time goes on. How much loss of quality you can live with is a personal thing and only you can decide.
In real life, my name is Wayne P. Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!
Feed the newbs, starve the trolls and above all enjoy what you drink!
I think metal-filtered coffee is less stable when stored than paper-filtered coffee, but then again I rarely make the latter (or make more than I can drink quickly), so I don't feel confident in saying so. What's your take?
I think the key is exposure to heat - you need the heat to extract, but the heat will then go on to convert flavor components (probably chlorogenic acids) in the coffee to worse tasting compounds. I have a few friends that were wondering how to improve their thermos coffee, and I suggested they make it the night before and refrigerate it before putting it in the thermos. Then, when they want coffee, pour some out and microwave it. So far, there seems to be anecdotal consensus that this does in fact make a better cup the next morning and later into the day. Try it - you might like it.
So cooling it quickly and especially refrigerating it should allow brewed coffee to "keep" for some length of time, at least a day?
In general, refractive index of even very well-filtered or centrifuged coffee will creep up over time (meaning the measurement of %TDS will increase over time). This is true even if refrigerated. There are different explanations for this phenomenon depending on whom you consult - one thought was undissolved coffee continues to dissolve into solution, but I just don't buy this explanation. Filtering with a 0.2micron syringe filter, or doing so after 10 minutes centrifuge - there just CAN'T be enough there to continue to extract. Small particles are the first to fully dissolve to the core - there shouldn't be anything left to change the %TDS.
So my thinking is some compounds are changing over time to other compounds that affect the refractive index - but not the actual solute. I couldn't tell you if it's lipids, or low temperature pyrolysis, or trace oxidation. I'll probably never know for sure, but I know enough that the "continuing to extract" explanation doesn't explain extremely clarified coffee changing about the same amount over a period of 5-6 days. One would also expect a coffee that has fines (like from a metal filter or french press) to change more, because it has more fines. But my few checks show it changes about the same amount.
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