Nutation: An Apology
September 20, 2015
Back in the 2013 World Barista Championships, I used a tamping style called ‘nutation’ for all of my espressos. Many of you have been asking about this technique via email so this week I’m going to explain what it is, how to do it properly and why I don’t recommend it.
I’d also like to take this opportunity to apologise for doing it at all.
Truly, I am sorry. Let me explain.
What is it?
To nutate, one rotates the tamper around the vertical while applying moderate downward pressure on the grinds.
Nutation is a novel tamping technique that’s been around for longer than I’ve been in the coffee industry (7 years. I’d love to know who coined it! edit: First discussed by North Sullivan 13+ years ago.) It’s commonly used by home baristas to slow down their espresso when grind size is fixed or they’re using pre-ground coffee that’s too coarse.
A regular tamping technique will compress the grinds, removing most major air pockets and minimizing void space between grinds. It’s important to note the “most” part in there. There’s still empty space amongst the grinds. This empty space allows the water to flow through. The more space there is, the faster the flow.
Nutation moves the grinds around in more directions than a regular tamp. It forces them onto each other, twisting and turning them until they lock together. I like to think of it as a tessellation of the grinds. Their shape and size hasn’t changed, but their edges are now interlocking. The result is a more dense, cohesive mass of grinds. This means there’s a lot less empty space between grinds, restricting the flow of water.
The easiest way to observe how drastically nutation affects density is tamp some coffee normally and take note of the tamper depth; then nutate and check the depth again. It’ll have sunk into the basket quite noticeably.
How to do it properly:
One major problem with nutation is consistency. How do you rotate a tamper at an angle with any semblance of consistency?
Short answer: you can’t.
Long answer: Rely on muscle memory and shot times. Do it a lot. Develop a technique with a consistent number of turns at an angle that’s easy to replicate. Monitor shot times to coach yourself towards consistency. Eventually, you’ll be able to get pretty good at it. Then apply that to your team of baristas. (Good luck!)
I also advise reducing the vertical angle with each spin so you finish up with a level tamp at the last moment. This helps create a level bed and produces much more consistent shot times.
I don’t recommend it.
Nutation is a quick and dirty way to slow shots down. It gets the job done, but it’s not optimal.
Nutation (probably) doesn’t create an even density between the outer and inner basket, because there’s a lot more pressure on the outside edge of the grinds. This could lead to unevenness, but I have no way of proving it.
It’s possible to calibrate a team of Baristas to produce nutated shots with similar brew times, but it’s not possible to determine if they’re doing it in the same way.
In regards to nutating with traditional espresso grinders, it’s quite harmful to extraction evenness. Traditional grinders struggle to create a narrow particle distribution. It’s best to grind as fine as you can to reduce the number of boulders (large grinds) they produce. Nutation requires a coarser grind setting which extends the particle distribution even farther from ideal.
One thing for sure is that nutation raises more questions than it answers.
I recommend avoiding Nutation, if you can.
When using a grinder like the EK43 for espresso (like I did for WBC 2013), it can sometimes be difficult to slow the flow of espresso enough to hit 25-30 second shot times; even if you’re at the minimum grind setting. This isn’t necessarily the grinder’s fault, and can be fixed pretty easily
If you’re struggling to slow your shot down, here’s a list of things you might want to fix before looking to nutation.
1. Flow Rate: I’ve seen some unrestricted machines approaching 600ml per 30 seconds where it’s nearly impossible to grind fine enough. The ideal range for me is 150-250ml per 30 seconds. Reducing flow rate to these levels will improve any machine/grinder set up. Most baristas don’t have easy access to the restrictors in their espresso machine, but it’s absolutely worth hiring a technician to fit some smaller ones.
I measure flow rate with a pitcher under an exposed group head. Run the pump for 30 seconds and weigh the pitcher afterwards.
2. Burr Alignment: Make sure your burrs are seated on clean, debris-free metal. When tightening the screws, tighten them little by little rather than one at a time. Check the concentricity of the burrs visually by spinning the rotating burr and checking for an irregular rotation. This can involve a lot of trial and error, but is absolutely worth it.
3. Roast Development: I don’t want to harp on about this too often, but a lot of specialty roasters don’t evenly develop their roasts (aka the inside is less done than the outside). This drastically reduces the brittleness of the beans, resulting in a much coarser grind no matter the grind setting. If you’ve done everything else, and your shots are gushing, it might be time to have a chat with your roaster. If in doubt, buy some coffee from other roasters and see if it’s more amenable to grinding. Having to use drastically finer grind setting for a particular coffee is an almost surefire sign of roast underdevelopment.
4. Pump Pressure: Pressure and flow rate are kind of the same thing in espresso. Because the coffee doesn’t form a complete blockage, it’s safe to say it doesn’t really experience 9 bars of pressure (especially not the lowest grinds). If you can’t change the restrictors, reducing pump pressure is your next best bet. Have a play with your espresso machine’s pump, aiming to hit the 150-250ml/30sec mark. Go all the way down to 4 bars if necessary. Don’t fret; 4 bars is still a lot of pressure, and you’ll still get your precious cremaz.
During the WBC I wasn’t allowed to adjust the pump pressure or flow rate, so I was forced to nutate. Long story short, nutating works. But try to avoid it if you have control over alignment, roast and machine variables. I apologize for any other messages I may have sent.
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