[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.