Bloom time: 30 seconds versus 60
Every pour-over recipe I have followed says to bloom the coffee for 30 to 45 seconds, and I had never questioned it. Then I read someone arguing that a longer bloom lets the grounds degas more fully and gives a more even extraction, so I spent a week brewing the same coffee two ways, alternating mornings, and tasting with as much honesty as I could manage before 8 a.m.
The constants: 15 g of a medium roast from a natural process Brazilian lot, 250 g of water at 94 degrees Celsius, the plastic cone dripper with a paper filter rinsed first, grind at the same setting on the hand grinder, and the same pouring pattern after the bloom: two pours of 100 g and 100 g with 45 seconds between them. Bloom water was 45 g both ways, enough to wet all the grounds with a little pooling.
The 30-second bloom: total brew time averaged 2 minutes 50 seconds over four brews. The bed was flat at the end, with a thin ring of fines on the paper. Taste was good, chocolatey, medium body, with a slight dryness on the finish that I have come to associate with this bean and did not think much about.
The 60-second bloom: total brew time averaged 3 minutes 15 seconds, and the difference was almost entirely the extra 30 seconds up front; drawdown after the last pour was only a few seconds longer. The bed looked the same. Taste was noticeably sweeter, with the dryness on the finish reduced, and a slightly heavier body. Two of the four mornings I would have called it clearly better. The other two I would have said it was the same cup.
I also tried 90 seconds once, out of curiosity. That one was a step back: softer, a bit flat, as though the water in the bloom had cooled too far before the main pours arrived. It probably had. So the longer bloom stays, at least for this roast. My guess is that the gain is bigger with fresher beans, which have more gas to release, and smaller with coffee that has been open for two weeks. I will check that when the next bag arrives. The cost is 30 seconds of standing in the kitchen, which I was going to do anyway.