Thermal Shock Coffee: What It Is and Why I’m Excited About It

We just released our first-ever thermal shock coffees, and I am beyond excited for you to experience them.

They are each remarkable, and come from Néstor and Adrián Lasso of Finca El Diviso in Colombia: an Ombligon Thermal Shock Natural, a Sidra Thermal Shock Natural, and a Thermal Shock Geisha that is washed. All three are really, really special.  The Ombligon, in particular, is one of the most unusual coffees I have ever tasted.

Watermelon Jolly Rancher. Cinnamon candy. Strawberry. Mulled wine. Amaretto.

Those are some of our tasting notes. If you are wondering how that list has anything to do with coffee, you are asking a reasonable question.

A big part of the answer is what happens to the coffee after it is picked. And that brings us to a term you may never have heard before: thermal shock.

I am still learning about this myself. Kelly Combs, a member of our green coffee buying team, writes the notes that introduce each of our coffee releases to our baristas. She put together a wonderfully detailed explanation of these coffees and their processing, and I have been working my way through it. My goal here is to share enough that you can appreciate what these producers are doing without needing a degree in microbiology. We will see how I do.

The People Behind the Coffee

Néstor and Adrián are brothers working in the mountains near Pitalito, in Colombia’s Huila region. They come from a coffee farming family, but they have taken the work at Finca El Diviso in a remarkably experimental direction, exploring unusual varieties and carefully designed fermentation processes.

I first enjoyed Néstor’s coffees while traveling in Europe (first at Nomad Coffee in Barcelona and most recently at 7g Roasters in Porto specifically) and have been impressed by what he is doing ever since.  This past Summer I scoured the Internet to see who might be importing some of his coffees.  When I saw these three listed on an importer’s availability list (nope, not telling), I called them and offered to purchase their remaining inventory on the spot without even tasting them.  

That is how interested I was in getting these coffees here - and confident I would love them.

The best way I can describe their approach is that they think like winemakers. The variety matters. Where it grows matters. The ripeness of the fruit matters. Then come a whole series of decisions about fermentation, temperature, time, and drying that help shape what we eventually taste.

There is a little mad scientist energy to it all. But the more you look at the details, the more you see how deliberate the work is.

First, A Little Coffee Processing Background

The coffee bean is actually the seed of a fruit we call a coffee cherry. After harvest, producers have to get that seed out of the fruit and dry it before it can eventually be roasted.

How they do that has a significant effect on flavor.

In a natural process, the coffee dries inside the cherry. In a washed process, the skin and pulp are removed, and the sticky fruit layer surrounding the seed is broken down and washed away before drying. There are variations within both approaches, but that is enough background to get us started.

Fermentation is part of this story, too. Yeasts and bacteria use sugars in the coffee fruit, producing compounds that can influence the finished cup. Producers can guide that activity through decisions about time, temperature, oxygen, and sometimes the addition of selected yeasts.

If you enjoy wine, sourdough, or beer, you already enjoy the results of someone paying attention to fermentation.

So, What is Thermal Shock Processing?

At its simplest, thermal shock means deliberately changing the coffee’s temperature quickly as part of processing.

Often, descriptions involve a warm or hot treatment followed by rapid cooling. But the term covers different protocols. The timing, temperatures, and surrounding fermentation steps vary by producer and by coffee.

Temperature is one of the tools producers use to influence what is happening during processing. It can change microbial activity and the pace of fermentation. A rapid temperature change becomes part of a larger effort to guide flavor development.

You will sometimes hear this described as “locking in” flavor. That is a useful image, but the science behind the exact flavor effects is still being worked out. What we taste comes from the whole process, including the variety, fermentation, and drying.

Here is the part I find especially interesting: even our three coffees do not follow the same recipe. The Ombligon receives its thermal shock before a fermentation stage with brewer’s yeast. The Sidra and Geisha receive theirs later in the sequence.

These are individual coffees receiving individual attention.

Three Coffees with Very Different Personalities

Ombligon Thermal Shock Natural

The Ombligon makes quite a first impression.

Ombligon is an uncommon variety associated with Huila. Its name comes from the Spanish word for belly button, a reference to the distinctive little protrusion on the cherry.

For our lot, ripe cherries go through an initial fermentation stage, a thermal shock, and then an oxygen-free fermentation with a little brewer’s yeast before drying.

The resulting coffee is intense and complex, with a creamy body and flavors that remind us of watermelon Jolly Rancher, cinnamon candy, strawberry, mulled wine, and amaretto. I do not want to be hyperbolic, but I had not tasted anything quite like it.

This is a coffee to brew, sit down with, and pay attention to.

Sidra Thermal Shock Natural

I think the Sidra might be the sleeper of the bunch.

Geisha has the name recognition. Ombligon has the intrigue of being the unusual new kid on the block. Sidra is a name I suspect many of our customers have not encountered, and I would hate for it to get overlooked here.

There is a beautiful interplay of candied fruit, herbs, and botanicals in this coffee. As I tasted it, I kept going back and forth between watermelon candy and something that reminded me of a gin and tonic. Then there was mint, almost spearmint, and an aromatic quality that had me thinking about blanc vermouth.

That fresh, fragrant herb character alongside the sweetness of the fruit is what makes this coffee so fascinating to me.

The Sidra moves through several fermentation stages, including time submerged with recirculated juices from the coffee fruit. After its thermal shock, it dries gently in a temperature-controlled chamber.

Of the three, this might be the one that surprises people most once they spend a little time with it.

El Diviso Thermal Shock Geisha

This is the most floral Geisha I have ever tasted. To me, it is like drinking roses.

I want to be clear about that because we use the word “floral” quite a bit when describing certain coffees, and sometimes it means a delicate aroma you have to pay attention to find. Here, the fragrance is off the charts. It is intensely floral and botanical, and that has really impressed me.

There is beautiful fruit character, too: white peach, apricot, papaya, berries, and limeade. Our roaster Shannon particularly loves the combination of lime and rose. That pairing gives you a good sense of how complex and unusual this coffee is.

Our Geisha is a washed coffee, which is a good reminder that thermal shock can be used within different processing methods. After initial fermentation stages, the cherries are depulped. The coffee then goes through a 60-hour fermentation without oxygen, followed by thermal shock and carefully controlled drying.

But the thing I keep coming back to is that fragrance. Even knowing what Geisha can be, this one has expanded my expectations.

Why this feels like a taste of the future

I keep thinking about how we talk about wine.

We are comfortable with the idea that a winemaker’s decisions help shape the character of a wine. We seek out particular producers because we appreciate their judgment and their craft. I think more coffee drinkers are beginning to understand coffee in that same way.

That is what excites me about these coffees. They give you a chance to taste the work and imagination of the people who produced them. Néstor and Adrián are making decisions at the farm that we get to experience here in Newport, one cup at a time.

To me, this feels like a glimpse of where coffee can go. There is still so much to discover about what this fruit can become, and producers like the Lassos are giving us some pretty compelling reasons to stay curious.

If you have ever wanted to taste something that expands your idea of what coffee can be, these are exactly the kinds of coffees I would encourage you to seek out. I am excited to share them with you.

You do not need to remember the fermentation stages. Just make yourself a cup and give it a little time.

Happy Brewing!