The Group Head Express

Why do espressos from one group run faster than the other?

BH Unlimited Update, Feb 21st 2022.

Here’s an excerpt from this week’s blog post : You’ve dialled in perfectly. You are weighing every single dose, distributing carefully, tamping perfectly flat with a calibrated amount of force — and yet, your shot times aren’t the same. After a few shots you notice it’s always the same group that runs just a few seconds faster — or slower — than the others. Perhaps you start to avoid using that group, and somehow the problem gets worse and worse. You’re careful about cleaning your machine and backflushing regularly, so you know that’s not the problem. Maybe you even call out a technician, and they tell you there’s nothing wrong with the machine. Does this sound familiar?

There’s at least two handfuls of reasons why your groups might not be running the same. This new post walks you through them all. First, there’s the quick fixes like making sure your baskets and blocks are identical. Then there are the more complicated explanations such as needing to bleed your group head to ensure it’s fully saturated with water, or exploring how, and when, and if you should replace a flow restrictor.

If you sense there’s a problem, there probably is. We’ve designed this post to help you check if there really is a problem, pinpoint the cause of a problem if it turns out there is one, and perhaps avoid the expense of calling out a technician. If you do need to call a technician, then you can at least make sure that you know exactly what needs fixing, so they can get you back up and running as quickly as possible.

If you don’t currently have a BH Unlimited subscription, that’s okay, this post is free to read.

Roasting Science

This week in Roasting Science , we take a detailed look at the main features of a typical drum roaster and explain how the choice of drum and burner design affects the machine’s capabilities. A double-walled drum insulates the beans from the heat of the burner underneath the drum — but, paradoxically, this allows for faster roasting. Insulating the drum reduces the risk of burning the surface of the beans, making it possible to roast at higher temperatures.

We then explore the advantages and disadvantages of the classic drum roaster design. Some roasters claim that the conductive heat supplied by classic drum roasters allows them to produce coffees that are more full-bodied, but in general it is difficult to design controlled experiments to compare different styles of roasting machines. Even if an experimenter manages to produce an identical profile on two different roasters — no easy feat — the optimal roast profile for different kinds of roasting machines is likely quite different, making such comparisons meaningless.


On Thursday in Petrópolis, situated in the mountains north of Rio de Janeiro, the city experienced 258 mm of rainfall in less than three hours. This brought on flooding and mudslides in the district of Morro da Oficina that has claimed the lives of more than 100 people.

Our hearts go out to the people of this beautiful place.

Our Editorial Policy

At BH we never do ads for 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 or because it shows you something you need to see. It’s as simple as that.

Roasting Science

Roaster Types
RS 1.02 • Features of the Directly Heated Drum
RS 1.03 • Pros and Cons of Directly Heating the Roasting Drum

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