Evaporation from Front to Back

BH Unlimited Update, Sep 17th 2022.

You know how bakers reckon they get better results and a nicer crust if they have a tray of hot water in the oven as they bake? The reasons why steam is beneficial to baking are manifold, but we only bring this up because when you look into the science of coffee roasting, you begin to realise that it is steam that’s responsible for a lot of the difficulties in managing a roast.

Bakers don’t have any issues with keeping the steam in their ovens, but with coffee roasters, the moisture that comes out of the beans just disappears right up the chimney (with the exception of certain recirculating air roasters like Loring). Then there’s the added complexity of a sudden arrival of steam during first crack — the probable cause of crashes in bean temp RoR; and then steam's sudden disappearance only seconds later — the probable cause of the ‘ flick of death ’ (a sudden acceleration in the bean RoR).

Just take a look at this data collected by James Davison , a chemical engineer and founder of Williamstown Roasters . These measurements were taken in a drum roaster, and show a distinct spike in moisture evaporation at first crack.

You’ve got to wonder whether adding some steam-injection capabilities onto a roaster might be a handy means of mitigating flicks. We’re hatching a plan on how to test that ATM — of course we’re expecting Prototype A will involve a steam wand.

So folks, we’ve put together a huge post for you on what happens to moisture during roasting. BH Unlimited subscribers who have been working through the Roasting Science online course will already be acquainted with the evaporation front . It’s a topic which has had very little direct study, so we go into plenty of depth there, too.

Roasting Science

In our Roasting Science course this week, we have begun looking at the physical changes that take place in coffee during roasting. Coffee beans lose mass and increase in size as water and carbon dioxide escape, becoming porous and less dense. These changes are essential in making it possible to grind and extract coffee beans.

The amount of mass loss is an important indicator of the degree of roast — and yet how the beans swell and lose mass during the roast depends on the kind of roaster being used, and the roasting conditions. A long, slow roast will never achieve the same mass loss as a fast, hot one, and this makes it very hard to compare results between different roasters. Even the variety of coffee plays a part: the cell wall structures of different varieties seem to break down at different rates.

There’s more than one kind of pore in a coffee bean. Different types of pore play different roles in a coffee bean

In this week’s lessons, we explore these conflicting results, and the role that the changes in the bean’s structure play in the final properties of the coffee, such as how quickly it goes stale, or how easy it is to grind.

BH Unlimited subscribers have advanced access to each new lesson as the course progresses.

The Coffee Buyer’s Guide to Colombia

In our Buyer’s Guide to Colombia , we look at two very different regions in the country that have each been recognised with Denominations of Origin (DO).

Santander was probably the site of the very first coffee plants grown in Colombia, but was in many ways a late bloomer. When Norte de Santander was in its heyday, Santander lagged behind and developed a reputation for poor-quality coffee — not helped by the fact that the only route to export was through Venezuela. In the last decade or so, however, Santander’s enterprising producers have overcome challenging growing conditions, and the DO is just one sign of how much things have changed.

The beautiful Camino Real, a pre-colonial road in the heart of Santander

The Sierra Nevada de Santa Marta, in the far north of Colombia, is the only growing region in the country that is not located in the Andes mountains. The Sierra Nevada is a separate mountain range that juts into the Caribbean sea, famed for its unique biodiversity. Culturally and geographically, this region is quite distinct from the other growing regions in the country, and the DO reflects this.

In this week’s lessons, we detail the dramatic changes in Santander’s coffee production over its history. Meanwhile, we explore how coffee growers in the Sierra Nevada de Santa Marta may play an important role in protecting the region’s ecosystem in the future.

Quick Links

Anyone lucky enough to be coming out to Melbourne for the Melbourne International Coffee Expo, aside from the WBC action, there’s a couple of side hustles going on which you should know about. Sub Zero , the original and still the best frozen coffee pop-up company, have announced an event to be held at Axil Coffee in the Melbourne CBD, for the two days immediately following MICE.

Don’t miss Scott Rao’s Melbourne roasting masterclass on the 1st of October at the St Ali Roastery. We can tell you from past experience visiting these fabulous workshops that Scott’s an early riser — class kicks off at 8am.

Also on the 1st of October, Samo Smrke is giving a talk on Espresso Grinding and Extraction Science at Victoria Arduino Australia, where he promises to present brand new data on — among other things — the role of fines in espresso extraction.

In case you actually are a home baker and wanted to check out a really good bread blogger on the subject of steam, check out this post by Maurizio Leo .

Cupping Bowls Back in Stock

Our beloved lightweight cupping bowls are back in stock at the Global Shop (shipping worldwide from Hong Kong). We also offer 40% off carton orders - perfect for a roastery or large scale cupping lab that needs no less than 192 bowls to get through the day.

An Ad-Free Learning Experience

At BH we never do ads for other company’s products on our website. There’s no product placement in any of our courses, newsletters or blog posts. Our only income comes from what you pay for your subscriptions. When you see machinery or coffee gear mentioned in any of our educational material, or featured in our course videos, we have chosen to use that equipment because we like using it, because we think it’s historically significant in the evolution of the espresso machine, or because it shows you something you need to see about modern coffee culture. It’s as simple as that.

Roasting Science

Bean Behaviour
RS 3.05 • Mass Loss
RS 3.06 • Swelling and Bean Structure

The Coffee Buyer’s Guide to Colombia

Growing Regions of Colombia
CBGC 1.18 • Santander
CBGC 1.19 • Sierra Nevada de Santa Marta

As always, we're just an email away if you have any queries! Have great weekends and we look forward to seeing you next time.

To the Boundaries of Coffee,
Team BH