What Happens if Coffee Bloom Time is Too Long? Why Doesn't Coffee Expand During Blooming?

Why Coffee Grounds Don't Expand During Blooming

In normal coffee brewing, during the blooming stage, water is poured over dry coffee grounds, which absorb the water and expand into a "hamburger" shape. When the coffee grounds do not expand during the blooming stage, it indicates a problem that we should identify and resolve.

Stale Coffee Beans

The most obvious reason is that the beans have lost their gases and are no longer fresh. The reason coffee grounds expand into a "hamburger" shape is mainly because after roasting, coffee beans contain a large amount of carbon dioxide gas. When the coffee grounds absorb water, they release this gas, which simultaneously "lifts" the entire coffee ground layer, causing it to expand into a bulge.

Of course, over time, the gases within roasted coffee beans are gradually released. Typically, coffee beans will de-gas completely in about 45 days. Coffee beans that have released most of their gases will not expand during blooming, and their flavor will also be diminished.

This timeframe is not absolute, as it depends on the storage environment of the coffee beans. When coffee beans are stored in a sealed environment with reduced oxygen exposure, they de-gas more slowly. If the packaging bag is frequently opened or the beans are directly exposed to air, the de-gassing process will be extremely rapid.

Here is an experiment from FrontStreet Coffee. The first image shows coffee beans that were stored in a coffee bag for 2 months before opening and brewing (the bag was never opened during this period). During brewing, the coffee grounds still expanded and formed a bulge, though not as prominently as in the beginning. The second image shows coffee beans that were not bagged after roasting but were instead exposed to air. When brewed after 20 days, the coffee grounds did not expand.

Therefore, proper storage of coffee beans is an important practice for maintaining a longer flavor life. FrontStreet Coffee suggests using the original coffee packaging bag for storage. Coffee packaging bags have one-way degassing valves that can regulate internal and external air pressure, and sealing strips to ensure the storage environment remains airtight. If you open the bag daily to take out beans and then reseal it, they can be preserved for about 30 days. At average daily consumption levels, you can definitely finish them before the gases are completely depleted.

Grind Too Coarse

This problem typically occurs when switching to new beans. When replacing with another coffee bean of a significantly different style, if you continue using the previously fixed grind setting, the blooming may not expand due to the grind being too coarse.

As FrontStreet Coffee often emphasizes when sharing knowledge about grind settings, due to factors such as variety, altitude, processing method, and roasting, not all coffee beans will have the same coarseness when ground at the same setting.

Therefore, choosing the correct grind size is very important. FrontStreet Coffee's grind calibration is performed using a sieve with 0.85mm apertures, and the grind size for pour-over coffee is selected to achieve an 80% pass-through rate on the sieve.

Very Light Roast

Very light roasts, due to being removed from the roaster early, have harder bean texture and contain less gas. Therefore, during blooming, they do not show significant expansion, behaving similarly to stale coffee beans, with the subsequent golden crema being thin. However, this does not affect their flavor.

Some lightly roasted coffee beans also show similar phenomena. During blooming, the coffee bulge is not obvious, with only a slight swelling, which is also a normal occurrence.