The roast date on the bag is the most useful number printed on it. A bag's flavour changes more in its first month than at any other point in its life. Buying recent and storing it right is the cheapest upgrade you can make to your coffee.
The degassing curve
Roasted coffee releases CO₂ for weeks after the roast. The shape of the curve is roughly the same for every coffee, but the timing varies by roast level.
- Days 0–3 after roast: heavy degassing. Beans hiss audibly. The bloom over-foams. The cup tastes muddled and the recipe doesn't work — water and gas are fighting each other through the bed. Resting is non-optional. Don't open the bag.
- Days 4–7: usable but uneven. Light roasts often still aren't open; mediums start to land.
- Days 7–14: peak window for medium roasts. Sweetness and balance are loudest. The recipe behaves predictably.
- Days 10–21: peak window for light roasts. Density takes longer to "open up" — light roasts often taste closed in the first week and bloom into clarity at day 12+.
- Day 30+: aroma starts dropping. Acidity flattens first, then sweetness. Bitterness is the last to go.
- Day 60+: stale. Drinkable, not enjoyable.
The curve speeds up dramatically once the bag is opened. An unopened bag at day 14 can taste like a freshly opened one. That same bag, opened on day 4 and left unsealed, can be tired by day 14.
When to open the bag
For a single-origin light roast, target opening between days 7 and 10. For a medium roast, days 5–7. The bag needs to vent some CO₂ for the recipe to work, but you also want most of the peak window ahead of you.
If you got a bag at day 1 because you couldn't wait, you can brew it — just expect the first few cups to be inconsistent. Don't blame the recipe.
Storage, ranked
In rough order of how well they preserve coffee:
- Sealed in original bag with a one-way valve, kept cool and dark. The valve lets CO₂ out without letting oxygen in. This is the bag specialty roasters use, and it's better than most home alternatives. Just close it tight.
- Frozen in airtight portions. Single-day or single-week portions vacuum-sealed or in airtight jars in the freezer. The freezer halts staling almost completely. Take a portion out, let it warm before grinding (5–10 min on the counter to avoid condensation), brew. This is the cleanest long-term storage there is.
- Sealed glass or ceramic jar with a rubber gasket. Decent. Better than an open bag, worse than a valve bag. Keep it dark.
- The bag, open, clipped or rolled. Bad but very common. Two weeks like this and the coffee has lost most of its peak.
- In the fridge. Don't. Refrigerator humidity transfers into the bag and dulls aroma. The temperature isn't cold enough to actually halt staling.
The four enemies
Coffee stales because of:
- Oxygen: oxidises the lipids that carry aroma. Biggest factor.
- Moisture: accelerates oxidation and pulls aroma compounds out.
- Heat: speeds every reaction. A bag on the counter near a stove ages faster than one in a cupboard.
- Light: degrades aromatic compounds directly. Clear glass jars on a sunny shelf are the worst case.
Cool, dark, dry, sealed. Pick three out of four and you're fine. Pick zero and the coffee is tired by day 14 even if the roast was great.
Buying cadence
A 250g bag at one cup a day is roughly two weeks of brewing. If you can finish a bag in 10–14 days, buying weekly or fortnightly keeps you in the peak window without freezer logistics. If you brew less often, buy smaller bags or freeze portions.
The temptation to buy a kilo because it's cheaper per gram is real. The math stops being cheap when half the bag goes stale before you brew it.
How to tell if a bag is past its peak
Three signs:
- Bloom is flat. No bubbles, no rise. The CO₂ is already gone.
- Aroma in the cup is muted even at standard recipe. The coffee tastes like the brewer instead of itself.
- Acidity has dropped without anything replacing it. The cup is rounder but also duller.
If two of three are true, the bag is past peak. Brew it (it's still drinkable), but don't use it to dial in or to evaluate a new technique. Use a fresh bag for that.