Coffee freshness bags and buttons and so forth- Science!

On America’s Test Kitchen they demonstrated how to tell the freshness of your coffee, and it had to do with determining the gas your coffee beans are giving off. If they can inflate a zip-locked bag, they are pretty fresh.

Okay… so what’s up with the vacuum-sealed bags of coffee? I’ve previously operated on the idea that oxygen = decay of pretty much everything, so the more of a “brick” the coffee, the better the vacuum, the less oxygen, the fresher. So if the bags are full of air, I pass them by.

On the other hand I didn’t really perceive that the coffee was actually better… in fact, it often seemed worse. So I stuck with cans when I could.

And now this whole “giving off gas” thing is messing with me. Judging by that standard, tight “bricks” are the worst possible coffee, because that must mean they are old enough to not give off gas and break expand the bag. So do I look for bags that seem to be on the bring of bursting? Because that means that the beans are pouring out gas? But haven’t they then given off all the gas they’re gonna? Couldn’t they be ancient, and their gas from months ago is trapped?

But this is all very science-y, so I ask the Dope. Una!? Calling Una! Do you know about the little bits of “coal” we grind and drink?

Help! I need to know how to find the freshest coffee!

We find that the freshest coffee comes from beans that are very oily. So fondle the coffee bags to determine if the beans are dry or oily (my wife does the buying, so I can’t give details on what to look for). Or go to Trader Joe’s. We find that their coffee beans are consistently fresher than e.g. Starbucks (in Michigan. May be different on the West coast.)

Freshly-roasted coffee is still giving off CO2 and various combustion-related compounds , not oxygen. Oxygen, as you surmise, is not good for coffee flavor. High-class coffee bags have little one-way valves in them to let gases (mostly CO2) out but not air in.

ETA: example of a coffee-bag valve

As for finding the freshest coffee, you can do the following, listed in order of freshyness:
a) roast your own (works best if you either live in a warm climate and can roast outdoors, or have access to a kick-ass ventilation hood, as it’s a smoky process)
b) find and patronize a local roaster
c) buy coffee with the date of roasting disclosed – the Whole Foods we used to go to in Austin posted the roast date on their bulk containers, for instance; I’ve also seen roasting date printed on bags for some brands
d) buy coffee pre-packaged in valve bags
e) buy coffee packaged in any kind of vacuum-sealed bag or can (cans are more often mass-produced than bags, which can be good or bad, depending on the QC of the producer)

As for how much freshness matters, it’s a matter of taste. Fresh but poorly roasted or badly brewed coffee sucks, while old but well-prepared coffee can be good.

But I still don’t understand what’s good/bad or happening…if the coffee in the bag is like a brick, does that mean the coffee is old and not giving off gas?

If the bag is puffy, is that good or bad or no way to tell?

And I have never noticed the valve working at all. you have to press it, don’t you? I’ve done that and nothing happened…

No, you don’t have to press the valve, it works all the time.

[ul]
[li]Puffy with valve = probably fresh (though it could just have a jammed valve).[/li][li]Brick with or without valve = probably roasted more than a day or two before being packed, but who knows how much more.[/li][li]Puffy with no valve and supposedly vacuum-packed = probably stale, but maybe very fresh, or maybe not noticeably either one. Four possibilities:[/ul][/li][ol]
[li]packed when very fresh, really too fresh for vacuum-packing, so the gas is CO2[/li][li]packed when very-to-somewhat fresh and still outgassing CO2, with faulty vacuum but tight seal, so the gas is a mixture that stabilized whenever outgassing stopped[/li][li]packed at some point after CO2 outgassing was over, with faulty vacuum but tight seal, so the gas is all the air originally packed with it[/li][li]packed at some point after CO2 outgassing was over, with a bad seal, so air has freely exchanged ever since packing[/li][/ol]
[ul]
[li]Taken out of original container of any kind, sealed into zip-loc bag, and later found to be puffy, as described on the show you mentioned = probably fresh and still outgassing CO2.[/li][/ul]

In short, while the zip-loc bag test may demonstrate that CO2 is still outgassing and therefore that the coffee is very fresh, this does not translate to reliable or useful information about other bags.

And no, you don’t necessarily have to press a coffee-bag valve for gas to escape it. The bag does not necessarily have to look inflated in order for there to be enough pressure to release gas. (This varies from bag to bag in my experience: some valves are looser and some are tighter.) If there *is *a valve and you press it and nothing happens, it only means that at that particular moment, there’s no gas to expel. On the other hand, if you have prolonged custody of a valve bag and it gets puffier over a day or two, the coffee is probably still outgassing.

However, all this about CO2 is mild hyperbole. In my experience, significant CO2 outgassing doesn’t last more than a day or two after roasting – and coffee roasted two days ago is still very fresh. Actually, if you roast your own, it’s recommended that you don’t use it until after it’s “rested” a day anyway. It’s best to use it within a couple of weeks, if time-since-roasting freshness is noticeable to you, though.

If your goal is better-tasting coffee, the four actions you can take for the highest ROI are:
[ul]
[li]figure out what kind of roast tastes best to you (e.g., I love a dark French roast, but many people think that tastes burnt)[/li][li]use a grind that matches your brewing method (e.g., you need a coarser grind for French Press than for filtered drip or percolated)[/li][li]use more coffee grounds per cup of water, up to a point[/li][li]make sure the water is only a few degrees cooler than boiling when it contacts the grounds (many automatic makers don’t get water hot enough)[/li][/ul]

Refinements you can make that may or may not make a difference you notice or care about:
[ul]
[li]minimize exposure to air and moisture after you buy it, whether the coffee’s already ground or not[/li][li]get more-recently *roasted *coffee[/li][li]get more-recently *ground *coffee[/li][li]drink more-recently *brewed *coffee (don’t let it sit or try to reheat it)[/li][li]if you grind your own beans, get a burr-grinder instead of a blade-grinder[/li][li]filter your water[/li][li]change brewing methods entirely[/li][li]switch from (cheap, usually mass-produced) Robusta beans to (more expensive) Arabica beans[/li][/ul]

If you use milk, cream, or sugar, those refinements are somewhat less likely to make a difference you notice.