🅢 = Story: I Never Left 

 

Many people don’t know that I have a degree in chemistry and a doctorate in pharmacy. Fat Miilk may be my second career, but it feels like I never really left the science.

 

Coffee is fun, but it’s also incredibly technical. The deeper I get into this industry, the more I realize how much my career trajectories actually blend together. Coffee is a science game! I want to know why something tastes the way it does. What happens when we change the temperature? The ratio? The time? What’s actually happening inside the coffee when we roast it, and why can one small adjustment make such a big difference?

 

This way of thinking feels especially relevant with Robusta because there’s still so much we’re learning. There isn’t a playbook to follow, so we consistently get to experiment, observe, taste, adjust, and try again.

 

In pharmacy, I learned that dosing, timing, and interactions matter. There’s a window, either broad or narrow, where everything works the way it’s supposed to.

 

It’s wild how I may have changed industries and careers, but the scientist in me has followed me everywhere. 

 

— Lan Ho, Founder of Fat Miilk

 

🅘 = Insight: The Robusta Window

 

At Fat Miilk, we roast to order, which gives us an intimate understanding of the beans and the process. With 10+ years in the specialty coffee industry, working in quality control, sourcing, sample roasting, and now production, I’ve never been more excited to share what we’re discovering with Robusta. — Kim Nguyen, Head of Coffee Quality and Sourcing

 

After cupping and dialing in tens of thousands of coffees throughout my time as a coffee professional, I’ve come to realize that certain coffees have windows. By windows, I mean there is a certain amount of space (within time, temperature, and ratio) where a coffee will taste its best when brewing, roasting, and cupping. Chasing that window can be difficult, but so rewarding.

 

Robusta’s windows vary depending on the task. The cupping and brewing windows are different from the roasting window, and the challenge for me has always been determining just how wide or narrow each one seems to be.

 

The Cupping Window

 

When cupping Robusta, I’ve noticed that the window for getting a decent extraction and clarity in the cup is quite wide. Whether it’s at minute ten or twenty, the extraction is efficient and rarely under-extracted or watery. With Robusta’s higher solubility, there is a more forgiving window in which a cupping can be optimized with a smaller dose of coffee.

 

The chances of the cup becoming muddled are higher as the coffee continues to sit, though, so I would recommend completing two passes within 25 minutes. After that, the cup quality gets heavier and the flavors become more convoluted.

 

The Brewing Window

 

When brewing Robusta, it’s easy to get a great extraction, but without tasting the full range, it can be tricky to dial in. The window can be a little narrower depending on the brewing method.

 

With the higher chlorogenic acid content in Robusta, espresso can translate as more bitter and heavy. But with the proper dial-in, the sweetness comes to the forefront and balances out that bitterness.

 

Batch brewing mitigates some of that heaviness by allowing more water to pass through the ground coffee. At the same time, a tighter water-to-coffee ratio prevents the coffee from tasting watery and better highlights the sweetness inherent in Robusta.

 

When phin brewing, a medium-fine grind allows the water to move through the ground coffee slowly while still dripping through the bottom of the filter at a consistent rate, helping prevent over-extraction.

 

Depending on the brew method, the optimal window may be narrower or wider. The more sensory data you collect, and the more you taste each brew, the easier it becomes to understand exactly what that window looks like.

 

The Roasting Window

 

The narrowest window I’ve found by far is the roasting window of Robusta. The cellular structure of Robusta is decidedly denser, with thicker cell walls that make it more difficult for heat to penetrate the seed while it’s in the roasting drum.

 

When roasting Robusta, it can be easy to bake the coffee if there isn’t enough heat to get through those thick cell walls. Too little heat can result in an undeveloped interior with a bitter, overdeveloped exterior, something we in the industry describe as over/under.

 

Because of this, the greatest challenge for me as a roaster is figuring out the ideal window of time and temperature for Robusta. Lower and slower can result in a baked taste, while higher heat and faster roasting can still leave the inside underdeveloped.

 

I’ve been able to hit that narrow window with my roast approaches, but not without plenty of trial and error after roasting for almost a decade at this point.

 

🅟 = Pulse: Finding Equilibrium 

 

Robusta’s window starts inside the seed itself.

 

Coffee is a dense cellular matrix. During roasting, heat moves from the surface toward the center while water vapor and gases build pressure inside the cells. As that pressure increases, the structure expands and becomes increasingly porous, creating pathways that later influence how water moves through the coffee and soluble compounds are extracted.

 

Robusta’s dense cellular structure makes managing this transformation especially important. The goal is to deliver enough thermal energy for development to occur throughout the seed without pushing the exterior too far ahead of the interior.

 

So when we talk about finding Robusta's “window,” we're really talking about finding equilibrium between heat transfer, cellular structure, chemical transformation, porosity, and extraction.

 

The window may be narrow like Kim said, but understanding why it is narrow gives us a much better chance of finding it.