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.
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 have that impression as well. Could it be that the fines continue to extract leading to bitter notes?
In well-filtered coffee what breaks down over time? How long does it take? Does refrigeration help?
Would a % TDS measurement of freshly brewed, well-filtered coffee be noticibly different from one made after the coffee was stored in a sealed vial at room temperature for a week?
I find that refrigeration does help. Hot coffee turns quickly for me - maybe in 30 minutes or less there are taste differences, even if there is no change in %TDS. Hot metal-filtered coffee that is kept hot (as in press pot brew in a thermos) turns quicker.
However, I can brew an AeroPress at double strength or more into a room temp mug, then put plastic wrap on top, and immediately into the fridge. It will keep to morning for sure, and responds very well to hot water dilution and/or microwaving.
I also have great results putting a french press brew into a good old paper coffee cup and let it cool naturally. The fines settle to the bottom of the cup, the temperature by the time I'm reaching the fines is probably approaching 90°F but the taste can be outstanding.
The only difference here is what we do with the heat.
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.
jpender Said:
Would a % TDS measurement of freshly brewed, well-filtered coffee be noticibly different from one made after the coffee was stored in a sealed vial at room temperature for a week?
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.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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?
Netphilosopher Said:
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.
I think I posted some early stuff on the refractometer thread back when. Fresh AeroPress diluted coffee at ~1.17 may go up to 1.25% in 4 days. I'm going by memory, as I'm still in the process of assessing my backup state after my data loss incident. The strength/time charts may be one of the casualties.
I recall having a cup of Starbucks brewed (paper filtered) started out at like 1.44% (going by memory) and after 6 days seemed to stabilize at 1.53-4% or so. I recall also doing some evaporation measurements, with little change in the sample residual - but it looks like in my spare time I'll have to re-do this.
And you are correct - using a refractometer to measure stored samples over more than a day or two is not really accurate. Which makes me wonder - the old way of certifying SCAA gold cup was to brew coffee using the prescribed method (brewing control chart), then send a sample in for testing. I believe that if they were using dehydration, this may work. But if they are using correlated refractometry now (since it's become the de-facto strength measurement method) then the strength measurements may be artificially high by the time they receive samples.
The more we try and pin down this coffee thing, it's like Heisenberg Uncertainty Coffee... LOL
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
That's my experience. I think that's why Flash-brewed iced coffee works as well as it does. Brewing hot coffee (or even espresso) onto ice yields a drink that is nice and cool, with little time for much of the aromatics to escape AND retarding the degradation of good flavor compounds into bad flavor compounds.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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