The thirty seconds right after the water just covers the coffee bed are a highly informative moment in pour-over brewing. When fresh beans meet hot water, the bed rises evenly and fine bubbles appear on the surface, like a mushroom cloud slowly breathing; with beans that have been stored longer, the bed barely moves and there is hardly any foam. This stage, known as blooming, is in fact an on-the-spot report on the freshness of the beans.

The bubbles come from the carbon dioxide inside the coffee beans. After roasting ends, the beans keep releasing gas, especially vigorously in the first few days, then decreasing day by day. During blooming, hot water drives the remaining gas out, which is what creates the swelling and the foam. Beans roasted within three or four days produce lots of fast bubbles, enough to crack the bed open; after resting for one or two weeks, the bubbles become gentle and even; after one or two months, the bed is basically silent. By watching the density and rhythm of the foam, you can roughly tell what stage a bag of beans has reached.

For light-roasted pour-over beans, too vigorous degassing actually harms extraction. Carbon dioxide clinging to the surface of the grounds blocks water from contacting the coffee, and the blooming step, using a small amount of hot water to release gas first, is precisely meant to clear the way for the extraction that follows. It is generally recommended to rest beans for five to ten days after roasting before brewing pour-over; for Ethiopian natural beans such as the fruity profile of the Guji region, once fully rested the berry and floral notes come through cleaner and brighter; washed beans degas a little faster, so the resting period can be slightly shorter.

The blooming technique itself is not complicated. After grinding, level the bed, then pour in hot water at about twice the weight of the grounds, for example 30 g of water for 15 g of coffee, circling evenly to wet all the grounds, then let it sit for thirty to forty seconds. Too little water leaves some grounds dry, while too much starts extraction early. As you pour, pay attention to the color of the foam: fresh light-roasted beans give whiter, denser foam, and the darker the roast, the darker the foam.

Beyond the foam, there are two other practical signs for judging resting. A pungent aroma when the bag is opened, and gas collecting in the grinder's catch cup during grinding, both indicate freshness; a faint aroma and obvious clumping after grinding mean the degassing period has passed and the beans are best finished soon. Dividing a whole bag into single-use portions, sealing them and refrigerating them can also slow the loss of flavor; just remember to let them come back to room temperature before grinding, and the extraction will be more even.

Next time you brew, take an extra look at those thirty seconds of blooming. Whether the bed swells enthusiastically and whether the foam is dense, reading these signals will give you a better sense of the condition of the bag of beans in your hands than checking the roast date alone.