The Puzzle

During testing of the Simple Smart Coffee (SSC) Brewer - both before and during our small crowdfunding campaign - we kept hearing the same feedback: users were experiencing "less bitter coffee."

At first, we didn't make much of it. The sample size was small, taste is subjective, and without knowing what brewing methods people were comparing against, it would have been irrational to draw conclusions.

But the reports kept coming. And then we noticed something curious about the SSC Brewer's flow profile: the bulk of water flow occurs during the last third of brewing (see our flow profile analysis).

This seemed paradoxical. Traditional coffee wisdom says "bitter compounds extract late." So shouldn't a brewer with most flow happening late produce more bitter coffee, not less?

We had a puzzle that needed solving. Or at least, a viable explanation.

Confirming the Reports

With limited resources, we couldn't conduct a large-scale taste study across multiple brewing methods. Instead, we focused on two specific questions:

Does the SSC Brewer actually produce late-stage bitterness?
If not, is traditional wisdom wrong, or is something else going on?

We took inspiration from Onyx Coffee's 2020 video where they split a pour-over brew into three phases and tasted each separately. We did something similar, but split our brews into 30-second samples.

After testing many light, medium, and dark roast coffees, the results were consistent: we do not get late-stage bitterness with the SSC Brewer.

Samples from a 2:18 minute brew - dark roast (30 second samples and 18 second for last one)

In the image above you can see a typical example from one test of a dark roast coffee (a 2:18 minute brew split into five samples).

For medium and dark roasts, we used the recommended standard brewing method. For light roast we used the modified method.

Tasting notes by shown sample:

Quite sour/sweet, but not too unpleasant
Really sour, maybe slightly lingering and a touch astringent.
Moderately bitter with some complexity
Hint of bitterness
No real bitterness... slightly coffee-ish water

Notice that about 50% of the brew (by weight) came in the last 20% of brew time, yet the final sample showed virtually no bitterness. This pattern held across all our tests.

So question #1 was answered: There’s no late-stage bitterness in SSC Brewer coffee.

Question #2 turned out to be more nuanced - and the details depend on roast level.

Two Different Mechanisms of Bitter Extraction

Note: This is a simplified explanation of the extraction. A more detailed account will be available soon on our EPO Science page.

First, let's clarify what we're talking about: the undesirable late-extracting bitter compounds. Coffee needs some bitterness for balance and complexity. Compounds like caffeine and chlorogenic acid lactones (CGLs) contribute pleasant, desirable bitterness—and these extract easily and early in any brewing method. Another recently researched bitter compound, mozambioside, is also easily extracted regardless of brewing method.

Interestingly, the problem late extraction compounds are different for light versus dark roasts.

The Roasting Chemistry

During roasting, chlorogenic acids (which make up about 8% of green coffee beans) undergo thermal degradation:

Chlorogenic Acids → Chlorogenic Acid Lactones (CGLs) → Phenylindanes

This progression accelerates as roast level increases from light to dark.

Lactones typically give pleasant, rounded bitterness that adds complexity to coffee.

Phenylindanes give a strong, lingering bitterness with a metallic or ashy edge. Here's the kicker: they are tens to hundreds of times stronger than caffeine by taste threshold. Even in trace amounts, they create the sharp, lingering bitterness associated with over-roasted or over-extracted coffee.

Approximate indication of typical compound levels by % of soluble solids

Phenylindane concentration is negligible in light roasts but rises sharply in medium to dark roasts.

Light Roasts: The Hydrolysis Problem

Light roasts retain high levels of chlorogenic acids (CGAs) and chlorogenic acid lactones (CGLs) - sometimes 3-4 times more than dark roasts. This abundance of CGAs and CGLs is precisely why hydrolysis is a particular concern for light roast brewing.

Hydrolysis: In hot, slightly acidic water, CGAs/CGLs can break down into quinic and caffeic acids over time. This process accelerates with higher temperatures and more acidity. There are slightly divergent accounts of how quinic and caffeic acids affect the taste of coffee; some accounts describe them as bitter, others say they aren’t bitter in themselves, but they accentuate perceived bitterness. Either way, they make coffee appear to be more bitter tasting

In a typical 3-minute brew, hydrolysis doesn't produce enough of these acids to significantly impact bitterness. But if the brew stalls - usually due to fines migrating and clogging filters - the extended contact time allows substantial acid production, resulting in perceived harsh, bitter coffee.

The SSC Brewer prevents stalled brews associated with fines migration. The expanded coffee in the encapsulated bed holds most of the fines in place. Any that do wash through only affect the paper filter – which is downstream of the extraction taking place in the coffee bed (separated by several millimeters of air gap). The extraction process never stalls due to fines migration.

For light roasts: a mechanism for late bitterness exists, but it cannot occur in the SSC Brewer.

Dark Roasts: The "Loaded Water" Effect

Phenylindanes are always present in medium and dark roasts. But here's what makes them interesting: they don't dissolve easily in clean water.

Phenylindanes are small, hydrophobic aromatic dimers (two molecules bonded together). Their chemical structure makes them resist extraction into pure water.

Counter-intuitively, water that has already dissolved other compounds extracts phenylindanes better than clean water. Here's why:

Clean hot water is highly polar and dissolves polar compounds first - acids, caffeine, and sugars extract readily in early brewing. As these polar solutes accumulate in the water, they disrupt its hydrogen-bonding network, fundamentally changing the solution's chemistry.

This disruption creates a more favorable environment for hydrophobic compounds like phenylindanes. Once brewing water becomes loaded with polar solutes, it can more easily dissolve and stabilize these less-polar molecules.

This explains why phenylindanes extract disproportionately during late phases of traditional brewing methods - during long drawdowns - when the water is already saturated with other coffee compounds. The solution essentially becomes a better solvent for hydrophobic molecules as it becomes "dirtier."

Pure Percolation: Why SSC Brewer Avoids Phenylindanes

The SSC Brewer's "pure percolation" design is key here.

Unlike nearly all traditional pour-over methods, the SSC Brewer does not create a coffee slurry upstream of the percolation extraction that would allow significant polar solutes to dissolve into the standing water.

The water sitting above the coffee bed contains only easily dissolved acids and sugars that migrated upward through diffusion or CO₂ bubble movement. This water remains relatively clean compared to traditional methods.

Because only this relatively clean water percolates through the coffee bed, phenylindane extraction is inhibited throughout the entire brewing process - even during the high-flow final phase.

For dark roasts: phenylindanes need "loaded water" to extract, but the SSC Brewer keeps water clean.

Conclusion

The SSC Brewer's reduced bitterness isn't magic—it's chemistry and fluid dynamics working together.

For light roasts, the design prevents brew stalling and fines migration, eliminating the extended contact time needed for hydrolysis to produce harsh quinic and caffeic acids.

For dark roasts, the pure percolation design keeps brewing water clean, preventing the "loaded water effect" that enables phenylindane extraction in traditional methods.

Traditional coffee wisdom that "bitter compounds extract late" is not wrong - it's just an incomplete statement. Whether those compounds actually extract depends on the brewing environment. The SSC Brewer creates conditions that naturally inhibit extraction of the specific compounds responsible for unpleasant bitterness late in the brew, regardless of roast level.

So, we don’t have proof of this conclusion, but we are content with this reasonable explanation of what is going on. As the puzzle was simply ‘why are we getting better coffee than we might of expected’ there seems no practical need to investigate further … unless new facts come to light.

Why Doesn’t SSC Brewer Coffee Taste Bitter?