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

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Friends often ask FrontStreet Coffee why the bloom during pour-over coffee does not form a "hamburger" shape. Is it because the beans are not fresh? FrontStreet Coffee supplies customers with freshly roasted coffee beans, which need to rest for three to four days after purchase to reach their best flavor when brewed. It is true that bean freshness affects whether the bloom forms its "hamburger," but many other factors are involved. Today FrontStreet Coffee will look at what those factors are.

Why Bloom?

Bloom, commonly called "blooming," is the preparatory step in pour-over where a small amount of hot water is poured evenly to wet the surface of the coffee grounds before the main pour. Its main purpose is to release gases from the coffee particles, mainly carbon dioxide. Generally, the closer the coffee is to its roast date, the more bubbling occurs during the bloom. Darker roasted beans hold less moisture and release more gas during blooming than lighter roasts; once the particles have expelled their gas and can absorb water evenly, extraction in the following steps becomes more uniform.

In short, during blooming the air between coffee particles expands with heat while large amounts of carbon dioxide are released. The temporary gap layer that forms between particles provides the space hot water needs to pass through the coffee bed during the main pour.

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 the beans affects the "hamburger" shape during blooming. Generally, lighter roasted beans do not form as attractive a "hamburger" as darker roasted beans and appear relatively flat instead. This is because darker roasted beans contain more carbon dioxide and release gas more vigorously, making the "hamburger" easier to form during blooming. Conversely, even very fresh light roast beans may not achieve the puffy "hamburger" you expect.

FrontStreet Coffee blooming dark roasted coffee beans

2. Coffee Bean Freshness

As mentioned above, blooming is for degassing, so fresher beans contain more gas (mainly carbon dioxide) and naturally create a more pronounced "hamburger" during blooming. If you do not see a continuously expanding "hamburger" during the bloom, it indicates the coffee may have been stored too long after roasting, so the carbon dioxide inside the bean cells has dissipated naturally — which of course means the beans are no longer fresh.

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

3. Coffee Grind Size

If the grind is too coarse, the surface area of water contact with the coffee grounds decreases and the degassing effect weakens naturally. With a particularly coarse grind there will be no "hamburger" at all regardless of other factors, because water poured in flows straight through the gaps between particles without a proper bloom, let alone forming a "hamburger."

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

If the grind is too fine, the contact surface with water increases, but such fine powder lets water sit on the surface without penetrating properly, producing a poor bloom and again no "hamburger." FrontStreet Coffee determines grind size with a standard No. 20 sieve, targeting 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 another important factor in blooming, since coffee grounds expand and release gas by absorbing heat. When the water temperature is lower, the grounds have not absorbed enough heat, water cannot quickly penetrate the particles to displace the air, and excess water drips straight 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 them is absolutely right or wrong. Generally, spiraling from the center outward during the bloom forms an attractive "hamburger" more easily.

Water flow rate also affects the bloom. Achieving a perfect "hamburger" with a large flow is more difficult and usually requires stable circular pouring, so a small flow is more suitable for beginners trying to get the perfect "hamburger."

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 beans, the blooming water amount is twice the weight of the coffee grounds, blooming for 30 seconds. After the bloom you can either pour all at once or use segmented pouring. FrontStreet Coffee will use sun-dried Yirgacheffe Red Cherry as an example to show 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, overall high sweetness, caramel and cream in the aftertaste, 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 a Chinese standard No. 20 sieve).

For technique, FrontStreet Coffee uses a blooming water amount twice the weight of the coffee grounds — 30g of water for the bloom, with a 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 of water for the bloom, pour directly to 225g, with a total pouring time of 2 minutes (including blooming time).

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

[Yirgacheffe Red Cherry Coffee Flavor Description]

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

Three-stage pouring flavor: overall mouthfeel shows distinct layers, with pronounced aroma carrying lemon fragrance, floral notes and fermented wine aroma. The entry is rich and juicy, with citrus and lemon acidity, weaker nutty flavors and honey notes in the aftertaste.

Single-pour extracts faster because of more water-column agitation, producing more nutty flavor but thinner layering. Segmented extraction has less agitation, and although there is soaking time, water seeps through the filter paper quickly, giving a more balanced extraction with distinct layers of aroma, ripe fruit and nutty flavor.

FrontStreet Coffee Recommendation

A bloom that behaves well starts with the right dripper, and for most people that means the Hario V60. Hario was founded in Tokyo in 1921 as a maker of heat-resistant glassware for research institutions, and its heat-resistant server is a familiar companion to pour-over setups. In 2004 Hario redesigned the V60's prototype into the shape we know today, naming it for its distinctive 60° cone angle and "V" silhouette, and launched it a year later. The cone and 60° angle force the water to flow toward the center before dripping into the server, extending contact between water and coffee and drawing out more aroma and flavor, while the signature single large hole lets water move freely, so flow rate depends largely on the brewer's control — and shows up directly in the cup.

That fast, controllable extraction is why the V60 shines with the floral and fruity coffees of the third wave. FrontStreet Coffee usually points to its Washed Gordin Cooperative Yirgacheffe, whose classic Yirgacheffe citrus, lemon and jasmine profile loves a V60, or to FrontStreet Coffee's Flower Champion with its rich tropical fruit, FrontStreet Coffee's Strawberry Candy for a Geisha-style cup, and FrontStreet Coffee's Mozart with its raisin character. If you prefer a heavier cup, the V60 also handles medium-dark beans such as FrontStreet Coffee's PWN Indonesia Golden Mandheling, a deep roast with low acidity and a thick, lingering body full of herbal and dark chocolate aroma with a faint earthy note, or FrontStreet Coffee's Brazil Queen Estate, which is low in acidity and very balanced with pronounced nut and cocoa aroma and clear caramel sweetness — good for pour-over, espresso or a moka pot. FrontStreet Coffee prefers the resin Hario V60 above all: resin blocks heat loss effectively and, in standard industrial production, is the easiest material to mold with the smallest tolerances.

Whichever bean you choose, keep the bloom generous. FrontStreet Coffee's light-roast Ethiopian lots such as Gordin and Flower Champion sit well in a V60 with 15g of coffee, a 1:15 ratio and water in the 90-91°C range, while the medium-dark Golden Mandheling and Brazil Queen Estate prefer slightly cooler water around 88-89°C. Pour twice the coffee's weight in water for the bloom — 30g for 15g of grounds — and give it 30 seconds before the main pour.