Reasons for Coffee Grounds Not Expanding in Pour-Over Brewing and How to Form a "Burger" Shape During Bloom

For more professional coffee knowledge, please follow FrontStreet Coffee

Often, friends ask FrontStreet Coffee why the bloom during pour-over coffee doesn't form a "hamburger" shape. Is it because the beans aren't fresh? FrontStreet Coffee provides freshly roasted coffee beans to customers, which need to rest for three to four days after purchase to achieve optimal flavor when brewed. While it's true that the freshness of the beans affects the bloom's "hamburger" formation, there are many other factors involved. Today, FrontStreet Coffee will discuss what factors affect the bloom "hamburger" in pour-over coffee.

Why Bloom?

Bloom, commonly referred to as "blooming" in English, is the preparatory step in the pour-over process where a small amount of hot water is evenly poured to wet the surface of the coffee grounds before the main infusion. The primary purpose of blooming is to release gases from the coffee particles, mainly carbon dioxide. Generally, the closer the coffee is to the roasting date, typically the more bubbling occurs during blooming. Darker roasted coffee beans contain less moisture and will release more gas during blooming than lighter roasted beans; once the coffee particles have expelled gas and can absorb water evenly, it allows for more uniform extraction in subsequent steps.

In short, during blooming, the air between coffee particles expands due to heat while releasing large amounts of carbon dioxide. The temporary gap layer that forms between coffee particles provides the necessary space for hot water to pass through the coffee bed during the main infusion.

Factors Affecting the Bloom "Hamburger"

FrontStreet Coffee will explore each factor: roast degree, freshness, grind size, water temperature, and technique.

1. Coffee Bean Roast Degree

The roast degree of coffee beans affects the "hamburger" shape during blooming. Generally, lighter roasted coffee beans don't form as attractive a "hamburger" as darker roasted beans, appearing relatively flat instead. This is because darker roasted beans contain more carbon dioxide and release gas more vigorously, making it easier to form the "hamburger" during blooming. Conversely, even very fresh light roast beans may not achieve the "puffy" hamburger effect you might expect.

FrontStreet Coffee blooming dark roasted coffee beans

2. Coffee Bean Freshness

As mentioned earlier, blooming is for degassing, so fresher coffee beans contain more gas (mainly carbon dioxide), naturally creating a more pronounced "hamburger" during blooming. If you don't see a continuously expanding "hamburger" during blooming, it indicates that the coffee may have been stored too long after roasting, causing the carbon dioxide within the coffee beans' cells to naturally dissipate, which of course indicates the beans are no longer fresh.

Whether it's beans from FrontStreet Coffee's physical stores or online shop, all are freshly roasted. When brewing fresh beans, they need to rest for three to four days to ensure their flavors develop properly.

3. Coffee Grind Size

If the coffee grind is too coarse, the surface area of water contact with coffee grounds decreases, naturally weakening the degassing effect. If the grind is particularly coarse, there will be no hamburger formation regardless of other factors. This is because water poured directly flows through the gaps between coffee particles without proper blooming, let alone forming a hamburger.

FrontStreet Coffee blooming coarsely ground coffee beans, no "hamburger" formation

If the grind is too fine, although the contact surface with water increases, the powder being too fine causes water to remain on the surface without penetrating properly, resulting in poor blooming. FrontStreet Coffee blooming finely ground coffee beans, no "hamburger" formation. FrontStreet Coffee determines grind size using a standard #20 sieve, with 80% pass-through for light roast coffee grounds and 70%-75% pass-through for dark roast coffee grounds.

FrontStreet Coffee blooming normally ground coffee beans, showing "hamburger" formation

4. Water Temperature

Water temperature is also an important factor affecting coffee blooming, as coffee grounds expand and release gas by absorbing heat. When water temperature is lower, coffee grounds haven't absorbed enough heat, and water cannot quickly penetrate the coffee particles to displace air, with excess water dripping directly into the lower pot.

FrontStreet Coffee using 60°C water for blooming, no "hamburger" formation

5. Technique

There are many blooming techniques: spiraling from inside to outside, from outside to inside, and center pouring with diffusion. None of these methods are absolutely right or wrong. Generally, spiraling from center outward during blooming more easily forms an attractive "hamburger."

Water flow rate also affects coffee blooming. Using a large water flow to achieve a perfect "hamburger shape" is more difficult and typically requires stable circular pouring movements. Small water flow is more suitable for beginners to achieve the perfect "hamburger shape."

FrontStreet Coffee blooming with large water flow, "hamburger" shape not obvious

FrontStreet Coffee blooming with small water flow, "hamburger" shape obvious

Pour-Over Coffee Steps and Techniques

When FrontStreet Coffee brews fresh coffee beans, the blooming water amount is twice the coffee grounds amount, blooming for 30 seconds. After blooming is complete, you can either pour all at once or use segmented pouring. FrontStreet Coffee will use sun-dried Yirgacheffe Red Cherry as an example to demonstrate the difference between single-pour and segmented pouring.

FrontStreet Coffee Yirgacheffe Red Cherry

Region: Yirgacheffe

Altitude: 2300 meters

Variety: Heirloom

Processing: Natural

Grade: G1

Flavor: Lemon, licorice, citrus, berries, sweet orange, with overall high sweetness, caramel and cream notes in the aftertaste, and black tea aroma in the finish

[FrontStreet Coffee Brewing Parameters and Technique]

FrontStreet Coffee's selected brewing parameters are: Hario V60, coffee-to-water ratio 1:15, water temperature 90°C, grind size BG#6S (80% pass-through rate with Chinese standard #20 sieve).

In terms of brewing technique, FrontStreet Coffee uses blooming water amount twice the coffee grounds amount, meaning 30g water for blooming, with blooming time of 30 seconds. With a coffee-to-water ratio of 1:15, the total water amount is 225g.

Single-pour (also called one-pour): After using 30g water for blooming, directly pour water to reach 225g, with total pouring time of 2 minutes (including blooming time).

Segmented pouring (also called three-stage pouring): After using 30g water for blooming, the second stage pours to 125g before pausing, finally pouring to 225g, with total pouring time of 2 minutes (including blooming time).

[Yirgacheffe Red Cherry Coffee Flavor Description]

Single-pour brewing flavor: Overall feeling is relatively gentle, with pronounced aroma, carrying lemon fragrance, floral notes, and mature orange aroma. Nutty flavors are evident upon entry, with citrus and plum acidity, and caramel and cocoa notes in the aftertaste.

Three-stage pouring brewing flavor: Overall mouthfeel shows distinct layers, with pronounced aroma carrying lemon fragrance, floral notes, and fermented wine aroma. Entry features rich juiciness, with citrus and lemon acidity, weaker nutty flavors, and honey notes in the aftertaste.

Single-pour results in faster extraction due to more water column agitation, producing more nutty flavors but with thinner layering. Segmented extraction has less water column agitation, and although there is soaking time, water quickly seeps through the filter paper, resulting in more balanced flavor extraction with distinct layers of aroma, mature fruit, and nutty flavors.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473