Fellow Aiden Bloom Settings Explained: Duration, Temperature by Roast

Bloom is the most misunderstood setting on the Fellow Aiden. Most people treat it as a binary—either bloom or don’t bloom—when it’s actually one of the highest-leverage variables in the entire brew.

Get bloom right and everything downstream improves. Get it wrong and you’re fighting extraction problems that can’t be fixed by adjusting temperature or ratio later in the brew.

What Bloom Does Chemically

When hot water first hits coffee grounds, CO2 trapped inside the cell structure of the bean begins to degas rapidly. This CO2 creates a physical barrier between the water and the coffee’s soluble compounds. If you don’t allow time for that CO2 to escape before the main brew begins, you get uneven extraction: some grounds are fully saturated, others are still off-gassing and partially shielded from extraction.

The bloom phase exists to saturate all the grounds simultaneously and let the CO2 escape before extraction begins in earnest. The Aiden’s bloom feature dispenses a small amount of water (typically 2–3× the coffee dose by weight), holds for a set time, then proceeds with the main brew.

Two variables control bloom effectiveness:

• Temperature: Higher temperature drives faster CO2 release and begins extracting soluble compounds earlier
• Duration: Longer bloom allows more complete degassing and more even saturation

How Roast Level Affects Bloom

Roast level is the single biggest determinant of correct bloom settings because roasting temperature directly affects CO2 content.

Dark roasts produce the most CO2 during roasting. They also have lower density and more porous cell structure, which means CO2 escapes quickly when water is applied. Dark roasts need shorter bloom times and can tolerate higher bloom temperatures.

Light roasts produce less CO2 but have denser, less porous structure. The CO2 releases more slowly. Light roasts need longer bloom times to fully degas, and they’re more sensitive to high bloom temperatures because the delicate aromatic compounds are easily over-extracted.

Medium roasts fall in between, with moderate CO2 content and moderate cell porosity.

Recommended Bloom Settings by Roast Level

Roast Level	Bloom Temp (°F)	Bloom Duration	Notes
Light	196–200	40–50 seconds	Delicate aromatics; longer bloom for even saturation
Medium-Light	198–201	35–45 seconds	Most flexible; good starting range
Medium	200–203	30–40 seconds	Balanced extraction window
Medium-Dark	202–205	25–35 seconds	Faster degassing; watch for bitterness
Dark	203–206	20–30 seconds	Very porous; short bloom sufficient

These are starting ranges, not absolutes. Your specific roaster, origin, and age of the bag all matter.

How Days Since Roast Affects Bloom

Fresh coffee (under 7 days off roast) has the highest CO2 content. You’ll see visible blooming—the grounds puff up and form a dome. This coffee needs longer bloom times because there’s more CO2 to evacuate.

Coffee at peak window (7–21 days off roast for most light-medium roasts) has degassed somewhat but still has enough CO2 for a strong bloom. Standard bloom settings work well here.

Older coffee (30+ days off roast) has much lower CO2. The bloom phase still helps with even saturation, but the degassing benefit is minimal. You can reduce bloom time by 5–10 seconds for very aged coffee without affecting extraction quality.

A practical rule: if you don’t see the grounds rising during bloom, the coffee is old enough that you can trim bloom time. If the grounds form a pronounced dome, keep bloom time at the longer end of the range for your roast level.

The Interaction Between Bloom Temperature and Duration

Bloom temperature and duration aren’t independent variables—they interact.

A longer bloom at a lower temperature produces similar degassing to a shorter bloom at a higher temperature, but with different extraction effects. Higher temperature extracts more soluble compounds during bloom itself. For light roasts, this can be desirable (boosting extraction of bright, fruity notes). For dark roasts, it can cause over-extraction of bitter compounds.

The safest approach: set bloom temperature based on roast level (use the table above), then adjust bloom duration based on days since roast and the results you observe. Treat temperature as the course adjustment, duration as the fine adjustment.

Sample Profiles by Roast Level

The following profiles illustrate what well-calibrated bloom settings look like in practice. Use them as concrete reference points alongside the table above.

Fresh Light Roast (7 Days Off Roast)

A freshly roasted light roast has high CO2 and needs a long, low-temperature bloom to degas fully before the main extraction begins. Rushing this stage produces uneven saturation and a cup that tastes simultaneously bright and flat.

Bean:      Kenya AA Washed (Light Roast, 7 days)
Dose:      40g  |  Yield: 600g  |  Ratio: 1:15
─────────────────────────────────────────────
Bloom:     197°F × 48 seconds
SS Pulse 1: 200°F
SS Pulse 2: 202°F
SS Pulse 3: 203°F

Tasting notes at these settings: bright citric acidity, blackcurrant, clean finish. The 48-second bloom is long enough to fully saturate the dense light roast grounds and let the CO2 dome collapse completely before the first pulse begins.

Medium Roast at Peak Window (14 Days Off Roast)

At two weeks off roast, a medium roast is in its ideal extraction window. Bloom settings can be standard—no extension for freshness, no reduction for age.

Bean:      Colombia Huila Washed (Medium Roast, 14 days)
Dose:      42g  |  Yield: 655g  |  Ratio: 1:15.5
────────────────────────────────────────────────────
Bloom:     201°F × 35 seconds
SS Pulse 1: 202°F
SS Pulse 2: 204°F

Tasting notes: milk chocolate, caramel, mild citrus in the finish. A 35-second bloom is sufficient at this age—the CO2 dome rises and falls completely within the bloom window, indicating even saturation before the main brew.

Dark Roast (Any Age)

Dark roasts degas fast and need less bloom time regardless of bag age. Extending bloom on a dark roast leads to front-loaded, hollow cups where the best compounds extract during bloom and the main brew adds nothing but bitterness.

Bean:      Sumatra Mandheling (Dark Roast)
Dose:      45g  |  Yield: 720g  |  Ratio: 1:16
──────────────────────────────────────────────
Bloom:     204°F × 22 seconds
SS Pulse 1: 205°F
SS Pulse 2: 205°F

Tasting notes: dark chocolate, cedar, low acidity, full body. The short bloom keeps the dark roast from front-loading. If your dark roast cup tastes flat and drops off quickly, you’ve bloomed too long—reduce duration before adjusting temperature.

Using the Aiden Profile Generator for Bloom

The Aiden Profile Generator calculates bloom temperature and duration from your bean inputs. Enter roast level and days since roast and it applies these relationships to generate a starting profile.

The generator produces the same bloom settings a knowledgeable Aiden owner would dial in after a few experimental brews—use it as your starting point, then adjust based on what you observe in the cup.

Reading Bloom Results in the Cup

After changing bloom settings, the effects show up in specific ways:

Too little bloom (short duration or low temperature for fresh coffee): The cup often tastes uneven—some notes are bright and others are dull. You might taste both sour and bitter notes simultaneously, which is a sign of channeling during the main brew. Extend bloom duration by 5–10 seconds.

Too much bloom (very high temperature or very long duration for aged/dark coffee): The bloom itself over-extracts, creating a front-loaded cup that’s intense at first but hollow in the finish. Reduce bloom temperature by 2°F or trim duration.

Good bloom: The cup tastes coherent—bright and clean from start to finish, with the notes you’d expect from the coffee’s profile. Extraction feels balanced rather than front-loaded or hollow.

Community Reference

The community profiles are a useful reference for bloom settings because they represent real-world outcomes rather than calculated estimates. When browsing community profiles, look at bloom temperature and duration for coffees similar to yours—same roast level, similar origin—and use those as a sanity check against your own settings.

Most successful community profiles for light roasts cluster between 196–200°F bloom temperature and 38–45 second bloom duration. For dark roasts, the cluster is 202–205°F and 22–30 seconds. If your settings are far outside these ranges and you’re having trouble dialing in, returning to these ranges is a good reset point. The community data reflects many owners’ trial-and-error converging on what actually works—it’s more reliable than general batch brewer advice that isn’t Aiden-specific.