The E61 Machine

BH Unlimited Update, July 31st 2021.

Do you notice a lot of machines these days have E61 group heads? You might even think it’s a bit retrograde to keep plugging away at technology from 1961. Maybe you’re trying to decide whether to buy one of these retro looking things, or if you should instead be getting into the flow profiling revolution and embracing the latest technology. Well one thing’s for sure, the latest technology is more temperature stable, but if it’s efficiency and durability you’re after, the E61 makes a lot of sense. It’s totally analog, totally elegant, and just about indestructible. But what makes the whole thing really magic is the concept of the thermosyphon.

Take a look at this very simple illustration from the originator of the E61, Ernesto Valente, which is taken from his original patent from 1960.

A thermosyphon helps to keep the espresso machine brew temperature stable by constantly cycling hot water through the group. But the true beauty of the system is in the way the system doesn’t need the machine’s pump to circulate the water around — that happens via convection.

In this machine, a heat exchanger (1 in the above illustration) passes through the middle of the steam boiler. The water inside the heat exchanger is rapidly heated above 100°C. The hot water is less dense than cooler water, so it rises and passes into the group head.

The E61’s group head is — believe it or not — designed to lose energy. It’s exposed, it’s not insulated, and it’s made of brass. Those three factors all help the water in the group to cool which helps avoid brewing with water that is ridiculously hot. Plus, when the machine sits idle, the cooler water in the group is more dense, so it sinks back to the bottom of the heat exchanger. This creates a circular movement, constantly supplying hot water to the group head.

That’s half the story — if you want to find out about the precise workings of the group head, and to find out what happens during brewing, BH Unlimited subscribers can head into Chapter 3 of The Espresso Machine online course and read our latest updates.


The Coffee Buyer’s Guide

This week in the Buyer’s Guide to Brazil we head to the coastal state of Espírito Santo. Espírito Santo is one of Brazil’s smaller states — about the same size as Estonia — but the second-biggest coffee producer in the country.

Around 75% of the coffee grown in the state is conilon, or Coffea canephora, grown on the low lying land closer to the coast. The highlands to the south and west of the state, however, produce some of Brazil's finest arabica coffees.

In the high peaks and cool climate of the mountains, coffee flowers late and matures slowly. As a result the harvest here begins in October, well after the main Brazil harvest hashas finished.


Double Grinding

Have you tried grinding your coffee on the coarsest grind setting, then grinding it again on your desired grind setting? Strange, surprising, and arguably very desirable things happen when you do.

The idea of adapting a multi-step grinding process for use in burr grinders has been around for a while. In the 2014 World Brewers Cup, the Czech champion Petra Střelecká was breaking open beans to remove chaff before grinding. The next year she parlayed this into a two-step grinding process, starting with a coarse grind and then regrinding at a finer setting.

At the 2017 World Barista Championship, the Japanese champion Miki Suzuki took the approach a step further; freezing the beans before each grinding step, in a deliberate attempt to increase the production of fines and to maximise the available surface area of her coffee. Since fines are the main contributors to extraction in espresso, increasing fines production can increase extraction — but overdoing it can cause flow through the puck to clog, causing channelling .

Here’s a new post (free access) on the BH Blog detailing our recent foray to the boundaries of grinding. One very surprising discovery for us was that you get way smaller bubbles in your crema after double grinding. Take a look for yourself:

Double grinding results in a thicker, more stable crema with smaller bubbles. On the left is crema from a standard shot, and on the right the crema from a double-ground shot. Both pictures were taken using a light microscope at 10x magnification.


The Espresso Machine

History, Form, and Function
EM 3.03 • The First Thermosyphons
EM 3.04 • How the E61 Thermosyphon Works


The Coffee Buyer’s Guide to Brazil

Growing Regions - Bahia, Espírito Santo, and Paraná
CBGB 3.05 • Introduction to Espírito Santo
CBGB 3.06 • Montanhas do Espírito Santo (DO)
CBGB 3.07 • Conilon Capixaba


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

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