Drink it fast, before it turns to sludge

April 27, 2006 7:15 AM

Why is freshly brewed coffee so much better than coffee that's been sitting around for awhile?

A mere half hour after brewing, my gourmet coffee has taken on a greyish hue and lost some of the potency of its flavor. Why? And why do I only notice this phenomenon with coffee and not tea or other beverages?

posted by junkbox to food & drink (32 comments total)

Does your coffee brewer use a hotplate?
posted by Jairus at 7:18 AM on April 27, 2006

I'm sure someone can get more science-y for you, but consider what gives coffee it's wonderful flavor: Oils. The longer your fresh pot sits there on the heating element, the more you're going to scald the brew. The oils dissipate and the acids and other nasties start to premiere in the flavor.

I could be off on this, but I really think it's the acids that start to show up when you let coffee sit. They make it taste "sour". There's certainly something to be said for naturally acidic coffee varietals, but that's another question
posted by GilloD at 7:19 AM on April 27, 2006

GilloD has it. Some good information here:

A given amount of coffee only contains so much of the flavorful and aromatic oils. After those oils have all been extracted, the water will extract acids and other bitter tasting elements. This is called over-extraction.

.

The problem essentially is that when you allow a coffee pot to sit over the hot burner, the heat accelarates the extraction of the oils. The longer it sits over heat, the more is extracted. For this reason, coffee hounds recommend that you pour your hot coffee off into a preheated carafe to extend its flavor life a litttle bit. Keeping it on the heat allows it to downgrade faster.
posted by Miko at 7:25 AM on April 27, 2006

I'm not sure on the chemistry here, but my coffeemaker puts the fresh coffee into a thermos carafe, which keeps it warm for a pretty long time. If I put it right into a really good thermos right after brewing, it's perfect drinking temperature eight to ten hours later. My wife and I agree that strong coffee seems to (emphasis on seems) taste better and "mellower" after a long sit. It seems like something acidic actually recedes. Anyone know if this could be true? Or is it just in our heads?

Of course, if you keep the coffee on a burner or hot plate after brewing, it gets burned pretty quickly, as has been said.
posted by BT at 7:28 AM on April 27, 2006

Is this really related to over-extraction, though? I thought extraction had to do with what happens when hot water hits ground coffee, and over-extraction resulted from moving too much water over too small a quantity of grounds. What happens after the coffee is brewed and the grounds are no longer in play may be a different phenomenon, no?
posted by staggernation at 7:30 AM on April 27, 2006

If the grounds aren't there there isn't any extraction going on.

In a sealed thermal carafe, all you're doing is losing heat. Exactly the same coffee, slightly colder. Whether or not you can feel that it's colder would be the thing at play in terms of whether or not it's worse.

In an open glass carafe on a hotplate, you're providing heat and losing water to evaporation. If you leave it long enough, you'll end up with coffee powder baked on. At all the points between "fresh-brewed" and "coffee powder baked on" there's less and less water to go with the oils and suspended particles that make coffee coffee.
posted by mendel at 7:35 AM on April 27, 2006

I think this clip will explain, but it will do so in Japanese.

Anyway, add salt to take away the bitter taste.
posted by Grangousier at 7:36 AM on April 27, 2006

Japanese television, is there anything you can't do?
posted by staggernation at 7:44 AM on April 27, 2006

I just keep a jug of the coffee around after it's made, and heat it in a water bath for the rest of the day if I want anymore. It works fine. Or I drink it cold, with ice, sugar and milk.
posted by jon_kill at 7:52 AM on April 27, 2006

Staggernation is right. Miko is answering a different question.

Oddly enough, this question is not answered in the coffee FAQ. My WAG is that the good stuff in coffee, the oils, are fairly volatile, and will either boil off of break down when the coffee sits on a hot plate.
posted by adamrice at 8:15 AM on April 27, 2006

The hotplates on all the coffeemakers I've seen are just too hot. They're usually just short of boiling, and as the level of coffee drops, they cook the coffee to an increasing degree.

I used to put a carafe of new coffee on a lab hotplate adjusted to keep it at drinkable heat (not near-boiling) The coffee stayed good much longer. Now I put it in a vacuum bottle.
posted by Kirth Gerson at 8:17 AM on April 27, 2006

I've been using the salt thing this week, and it does seem to work to make stale coffee less horrible.
posted by OmieWise at 8:18 AM on April 27, 2006

This is pretty much exactly why I get Americanos over brewed coffee. Always fresh. :) My brew machine at home hasn't been used since July 13, 2005 when my wife bought me a La Pavoni Europiccola for my 40th birthday. Of course, then you have to spend another $150 for an even remotely acceptable cone burr grinder.
posted by smallerdemon at 8:21 AM on April 27, 2006

adamrice: that's exactly what I was trying to say. Extraction became a red herring; it's the wrong word for what's happening on the hot plate.

It's the sitting on direct heat that causes the oils in the coffee to degrade faster, leaving the bitter acids behind to take flavor prominence. Putting the coffee into a preheated carafe helps it keep the full flavor a bit longer.
posted by Miko at 8:39 AM on April 27, 2006

The problem lies in the heating element in the machine that keeps the carafe hot. It literally burns the flavorful oils in the coffee which degrades the taste and adds considerable bitterness. (This is similar to why overcooked garlic tastes horribly bitter, even though raw and perfectly-cooked garlic does not taste bitter at all). And, since there is less flavor, it can also accentuate the sour acids inherent in coffee as there are less flavor notes to compete with it.
posted by 1024x768 at 9:00 AM on April 27, 2006

miko: Acids are sour.
posted by 1024x768 at 9:05 AM on April 27, 2006

Oy. You get what I'm saying. They don't taste good.
posted by Miko at 9:17 AM on April 27, 2006

Also, since we're literal today, by "preheated carafe" I mean a vacuum-style carafe that is not at all connected to any source of electricity, preheated with hot water so it does not cause the coffee to cool. I refer not to the carafe designed to sit on the coffeemaker burner.
posted by Miko at 9:18 AM on April 27, 2006

I'm not trying to be critical, I'm just feeling a bit anal-retentive today, sorry. :-/
posted by 1024x768 at 9:23 AM on April 27, 2006

So, coffee is an extremely chemically complex substance. It's much more complex than wine, for instance, but is generally not treated as delicately as wine is -- we leave it in pots on burners for hours, take it to work in a thermos, reheat it in the microwave. Fine. I'm a coffee snob, and I do this too. However, understand that coffee is fragile, and it's going to be affected by how it is treated.

My personal "best practices" procedure for freshness is to roast it, seal it overnight, then grind enough beans for the amount of coffee I expect to be drinking within the hour. When I just want caffeine, I'll brew up a pot of coffee in my auto-drip, but when I want something delicious, I'll grind up 1-2 cups worth of beans, then use my Swiss Gold to make a cup with nearly-boiling water from a kettle. Drink it immediately! Mmm mmm yum.

I know some "super-tasters" that won't drink coffee that's been sitting even for 10-15 minutes in a warmer, but for me, I don't really notice an important difference for about a half an hour either, so long as it hasn't cooled down. I'll certainly drink coffee that's been in the carafe for 1-2 hours, because sometimes (often) I just want some coffee-flavored caffeine.
posted by Hildago at 9:33 AM on April 27, 2006

Some hotplates are hotter than others. You can make your coffee last longer and taste better by 1) stirring (I learned this from coffeegeek.com and it does make a difference) and 2) removing the coffee from the hotplate now and then to keep the overall temperature down. But as said above, the best solution is to buy a vacuum thermos and pour your fresh brew straight into that.
posted by _sirmissalot_ at 9:43 AM on April 27, 2006

If you're interested in not leaving your coffee sitting around (i.e., brewing a cup at a time), look at Single Serve Coffee for some options.
posted by staggernation at 9:50 AM on April 27, 2006

I'm not trying to be critical, I'm just feeling a bit anal-retentive today, sorry. :-/

No prob. my contributions were a little sloppier than I generally try for.
posted by Miko at 9:58 AM on April 27, 2006

I was hesitant to contribute to the din because there were already 20-odd comments, but what the hell.

First, volatile oils. Coffee aroma is, well, aroma molecules escaping to the vapor phase. In some cases things can smell for hours, days, years, sometimes a smell is transient and fleeting.

If you are familiar with perfumery, they describe them with "top, middle, and base" notes. The top notes are the ephemeral, short lived smells. As the cologne wears over the course of a day, the base notes will become prominent. This is partly because your nose becomes attenuated so some smells, but also because these top notes sometime evaporate faster. Coffee has a number of volatile compounds, which dissipate over the course of standing.

Ester hydrolysis. This is more speculative, but coffee, like most things that smell, have some esters, among other things. These tend to be some of the more labile (reactive) molecules. Ester hydrolysis yields an alcohol (not only ethyl) and a carboxylic acid. I am not sure whether what we describe as acidity in old coffee is actually acidity, or something more like astringency.

I also found this. Furfuryl mercaptan is an odd duck. Mercaptans (organosulfurs) tend to stink. Bad. But furfuryl mercaptan is a pleasant, nutty coffee smelling compound (present in coffee). These people say it degrades pretty readily in the presence of iron ion.
posted by oxonium at 10:28 AM on April 27, 2006

I worked at Coffe Bean & Tea Leaf Co. and we had to take classes on exactly this kind of stuff.

Coffee bitterness can happen from one of three sources: the roasting process, the brewing process, or the aging process.

The roasting process can make coffee bitter, because the initial heat breaks down many of the chemicals in coffee. The oils degrade, and so does the caffeine. Somewhere along the line, Americans started to believe that dark-roast coffee was a good thing. Sure, it is, for espresso. Not so for drip. Lighter roasts are finally starting to make a comeback, and they not only have more aroma but also more caffeine!

The brewing process can ruin coffee if the water is too hot, the water is too cold, or if it brews for too long. This is why it's so easy to screw up coffee in a french press. Temperature is difficult to control properly and human judgement often lets it brew for far too long. The recommended temperature is about 215F and the time is a function of how much you're brewing at a time. These brewing times are still not long enough to reduce the caffeine by any noticable amount. Notice that temp is actually above boiling...it's mildly pressurized.

The aging process will make the coffee bad in two ways. It will continue to break down the oils that give it its flavor, and it will continue to break down the caffeine. Some of this happens due to heat, but some of it is set in motion simply by the coffee having been brewed. For this reason, it is generally recommended that you absolutely avoid coffee over 1 hour old, whether from CBTL (1 hour max is policy), Starbucks (have no clue), or Mr. Coffee (up to you to decide). Also, if you enjoy the aroma, don't let it go cold. The aroma is carried off by the coffee steaming, and the overall body needs to be at least 200 to effectively carry it into the air (although some will still be discernable even at lower temps). Once it is brewed, please don't put it on an above boiling surface or in the microwave, as these will obliterate the flavorful aromas in well under the hour pointed out above.

Oh yeah, if you grind coffee, it is best if you use the grinds within an hour of having done so or it will never be able to achieve full flavor potency when brewed due to air exposure.
posted by mystyk at 10:36 AM on April 27, 2006

Looks like I was closer than I thought. Something that's bouncing around my head that may or may not be true: It's best to use beans within two weeks of the roasting? Same logic here. Although, I've been drinking some beans that are maybe 2 months old (Eek!) and it's not too awful, but certainly not in the prime.
posted by GilloD at 11:00 AM on April 27, 2006

Americans started to believe that dark-roast coffee was a good thing. Sure, it is, for espresso. Not so for drip.

I feel like a broken record, but: this is a matter of taste. Some of us like both dark roast and lighter roasts; I myself have the former in the evening, when the lesser amount of caffeine is actually desirable. I have no objection to your liking coffee the way you like it; I'd appreciate the same courtesy.
posted by languagehat at 11:43 AM on April 27, 2006

Others have explained the problem -- the essential oils either dissipate, are scalded, or turn rancid, if not brewed optimally. Here is one solution: the Krups FMF5. It brews the coffee into a thermos. The oils do not dissipate and the coffee is not overbrewed. Just use freshly ground coffee and you're golden.

This is not perfect, unfortunately. It helps if you pour hot water into the thermos before brewing, otherwise the coffee cools down too much by losing heat into the cold steel thermos.
posted by Araucaria at 11:52 AM on April 27, 2006

Hmm, just found a lot of negative reviews for that coffee maker on Amazon. Maybe it's better to simply buy a separate thermos.
posted by Araucaria at 11:56 AM on April 27, 2006

Those K-cups are pretty disgusting, too. Not a great solution.
posted by Miko at 12:47 PM on April 27, 2006

They have a Krups at work (not the one Araucaria linked to) that brews into a vacuum carafe, and even though its devotees grind the beans immediately before brewing, the output is not impressive. I bring a thermos from home. (Can we call them dewars instead? Thermos is y'know - trademarked.)
posted by Kirth Gerson at 1:42 PM on April 27, 2006

Looks like I was closer than I thought. Something that's bouncing around my head that may or may not be true: It's best to use beans within two weeks of the roasting? Same logic here. Although, I've been drinking some beans that are maybe 2 months old (Eek!) and it's not too awful, but certainly not in the prime.

Oh man, yes. Coffee is best when it's consumed within a couple days of being roasted.

The reason is that air is bad for coffee. When the beans first get roasted, they release CO2, and as this leaks out, it keeps air from getting inside. But after about 12 hours the CO2 is gone, and air starts to get in. After a couple of days, you've lost a good deal of the flavor of the coffee. It's certainly still drinkable, but it's not "ideal". I'm not sure what it would taste like at the 2 month mark..
posted by Hildago at 5:14 PM on April 27, 2006