Why Does Coffee Bloom Not Form a Dome During Pour-Over? What to Do When Coffee Grounds Don't Expand?

Introduction

When brewing coffee, as hot water contacts the dry coffee grounds, a large "burger" shape forms, which is quite satisfying. However, sometimes after starting to pour water, the coffee doesn't form this "burger" shape. What's going on?

Reason 1: Coffee Beans Are Not Fresh

During the initial bloom phase, coffee expands because the beans contain carbon dioxide gas after roasting, which expands and releases when it encounters water. However, coffee beans continuously release gas after roasting, and when the gas is nearly depleted, they won't expand into a "burger" shape when encountering water. The amount of gas in the coffee precisely indicates the freshness of the coffee beans. Therefore, FrontStreet Coffee determines the freshness of coffee beans based on the degree of burger expansion during blooming.

As for why the optimal tasting period for fresh coffee beans is about one month: because the entire carbon dioxide release process for most coffee beans ends around 30 days. However, this is not absolute—some coffee beans may have a longer gas release time (also related to storage methods). Therefore, using the burger expansion degree during blooming to confirm coffee freshness is a scientific method.

Reason 2: Coffee Grounds Are Too Coarse

The coarseness of coffee grounds also affects the expansion state of the coffee. When coffee is ground coarsely, the coffee particles become larger, requiring more time to become fully saturated with water, resulting in poor gas release effects. Therefore, the expansion degree will be smaller, and the center of the "burger" may collapse. This phenomenon is caused by overly coarse coffee grounds combined with excessive blooming time.

Even if the grind exceeds the coarse range suitable for pour-over coffee, water will flow into the lower pot due to gravity before being fully extracted. In this case, no expansion state will occur.

Therefore, choosing the correct grind size is very important. FrontStreet Coffee's grind calibration uses a 0.85mm aperture sieve for calibration, selecting a grind size with an 80% pass-through rate for pour-over coffee.

Reason 3: Water Temperature Is Too Low

Water is the main medium for extracting coffee. The higher the water temperature, the more active the water molecules become, and the more efficiently water penetrates the coffee grounds. Conversely, the lower the water temperature, the more stable the water molecules, and the less efficiently they penetrate the coffee grounds. Therefore, when blooming with low-temperature water, gas release from the coffee grounds is slow, making it difficult to form a coffee "burger." Through experiments, FrontStreet Coffee has found that with other parameters stable, water temperature above 80°C can form a coffee "burger." However, for general brewing, FrontStreet Coffee still recommends using 86-93°C.

Reason 4: Light Roast Level

The deeper the coffee roast level, the looser its internal fiber structure, resulting in better water absorption and gas release properties. Conversely, the lighter the coffee roast, the more complete and dense its structure, with poorer water absorption and gas release properties. Therefore, some extremely light-roasted coffees won't form a large "burger" even when fresh.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473