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

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

The density of ground vs. unground coffee

Does ground coffee take up more, less, or the same volume as whole bean coffee? If I want two scoops of ground coffee, how many scoops of whole beans should I put in the grinder?

To find out, I put two scoops* of coffee beans in my blade grinder and ground it fine. After putting it into a plastic container, I gently shook it to get the coffee to settle, as it would in a package of ground coffee.

The result: pretty darn close to the same volume.

Two scoops (16 grams) of coffee, whole and ground

* The scoop I used is from an Aeropress, and is somewhat larger than a typical coffee scoop. According to a scale, two scoops of coffee is just under 16 grams.

Re-roasting coffee beans

My brother recently sent me some coffee (Kenya Peaberry Thika Gethumbwini) that was supposed to be really good. For what it’s worth, it had a rating of 96 on coffeereview.com. I can’t vouch for the validity of those ratings, but surely the rating must mean something. Unfortunately, it turned out to be very sour, no matter what I did with the temperature and brewing time.

I’m not an expert in coffee flavors, but it also tasted kind of “planty” or “green” to me. From what I can find on the internet, this combination of factors suggests that the berries were possibly underripe when picked, and that perhaps they should have been roasted darker. I almost threw out the coffee, but then I had the bright idea of re-roasting them.

Supposedly the beans should get up to about 450-475 degrees inside, so I heated my cast iron dutch oven up to 500 degrees on the stove (an infrared thermometer was really handy here) and tossed in some beans. Then I turned the heat way down, covered, and stirred occasionally. I kept checking the temperature to make sure it didn’t get too hot. The beans occasionally crackled and jumped a little, and a bit of smoke came out every time I opened the lid. It smelled a little like burnt popcorn. The beans were on the stove for maybe 5-7 minutes, and at the end, I poured them into a collander and shook them around to cool. Here’s a shot of some beans before and after:

Coffee before and after second roasting