Do I really have to grind coffee right before brewing it?

3 03 2010

Coffee people always say that you should grind your coffee immediately before brewing it, because once it’s ground there’s a lot more surface area, which allows the flavorful stuff in the coffee to oxidize. Is it just a subtle difference that only serious coffee snobs would notice, or is it noticeable by anyone? How long can you wait after grinding before it starts losing flavor? This calls for a taste test.

The coffee is a light roast Ethiopian Yirgacheffe from Metropolis, and it was roasted 15 days ago. Yesterday morning, I tested four batches, ground at different times.:

  • Freshly ground (a few minutes before brewing)
  • 9 hours ago
  • 24 hours ago
  • 7 days ago

Each batch was 16g (2 Aeropress scoops) of coffee, ground fine (not quite as fine as espresso) in my blade grinder, and was stored in a small airtight plastic container. This morning I brewed them all in the Aeropress. I preheated the Aeropress with hot water so that the first cup of coffee wouldn’t be made with colder water than the later cups.

I brewed the coffee with my standard Aeropress method: Fill the measuring cup up to the 2 mark, pour into the chamber with coffee, stir for 15 seconds, then press. The water was close to 185 degrees each time. Since the coffee that comes straight out of the Aeropress is pretty concentrated, I diluted with an equal amount of water (although this is actually a little bit more dilute than I usually have it). Finally, I added 1/3 teaspoon of sugar to each cup.

My observations (keep in mind that I’m almost completely uneducated in coffee tasting):

  • Freshly ground: brighter acidity, richest flavor. I’ll use this as the baseline of comparison.
  • 9 hours: very similar to the freshly-ground coffee, although a bit mellower; less “bright” notes.
  • 24 hours: some of the fruity flavors have faded; a bit less flavor in general.
  • 7 days: duller, significantly less flavor overall.

Surprisingly it’s hard for me to decide whether I preferred the freshly-ground coffee or the 9-hour coffee. The freshly ground coffee was slightly more flavorful and the acidity was sharper, but I did enjoy the mellowness of the 9-hour coffee. As the coffee cooled, it became difficult to tell the difference between the two.

The 24-hour coffee was different from the freshly-ground stuff, but not hugely so. Without a side-by-side comparison, I wouldn’t have been able to tell that it had been ground a day before — there’s probably more variability in my coffee day-to-day just because of different brewing parameters.

The 7-day coffee really wasn’t as good as the others, but it was still more flavorful from, say, a coffee from Starbucks. (I don’t mean to pick on Starbucks specifically — it’s just that they’re a consistent baseline to compare to.)

This test was far from perfect and there are many possible confounding variables; some of the differences in flavor could have been due to different-sized grinds, temperatures, and brewing times. But at least I’ve learned that grinding up to a day in advance doesn’t really make a big difference in the taste of this coffee. It’s possible that there would be larger differences for fresher coffee, or for better coffees — although this stuff is pretty darn good.

Update: I made coffee again today, and after a couple of sips, I thought, “this coffee tastes pretty dull and boring.” Then I remembered that it was coffee that I had ground two days ago, so it seems that the loss of flavor is definitely noticeable after two days.



One response

28 02 2012
Lee Laird

I’m curious if there are other factors that might mitigate the changes experienced between the coffees. What if you put the ground coffee immediately into a zip-lock bag, and placed it into the refrigerator. Would this retain more of the immediacy flavors?? I would be interested to know.



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