I have been perplexed for a while by the use of the term "nutating" in espresso preparation. Nutation is defined in various ways here or here or even here.

It used to apparently be a fancy way of describing the nodding of the head.

In botany, it refers to the slight bend a plant may make as it grows.

In astronomy, it is the wobble in the oscillation of the precession of the axis of a rotating body.

None of these terms fully capture the idea of the motion I think we all assume we understand in our colloquial use is such phrases as "nutating tamp," but perhaps one of the reasons we do not get consistent results is because we are all doing our "nutating" tamp a bit differently.

In truth, to really be a true nutating motion when we tamp, we would have to wobble the tamper from side to side a bit while rotating. Okay, yes, that DOES probably happen, but not by intention, I don't think. Unless, I am wrong, most people are simply spinning or rotating the tamper while applying pressure. The major variables here are the amount of pressure applied and the amount of spinning/rotating done.

My personal experience is that any form of true nutation (i.e., wobble) is undesirable are it makes the puck uneven. I have also found that excessive pressure with the relatively asymmetric and dynamically changing forces of rotation can lead to channeling. So, what I tend to do is more akin to light polishing. Essentially I use only the weight of the tamper for my final "nutating" step and I simply rotate the tamper. This reveals any asymmetry because if the puck is not level, the tamper will wobble a bit as it rotates, which I suppose is actually the nutation.

So in fact I am really doing an anti-nutating step, I guess.

Anyway, I would be very interested to hear other people's thoughts about this topic, what they do, what their experience has been, and what the thoughts are on standardizing what is meant by nutating, which may not be nutation at all.

drdna wrote:In astronomy, it is the wobble in the oscillation of the precession of the axis of a rotating body.

Indeed...I think this description comes the closest to describe what is happening when I apply it to my tamp.
I grind straight into the basket, weigh for the amount I want. The grounds from my Macap are light and fluffy, no clumps...I give the basket a slight shake side to side to level the grounds. Then with the tamper and lightly contacting the grounds the "nutulating" occurs (with a slight rotation of the tamper) as it begins to compress the coffee. As I approach the point (determined by feel) of compression, the tamper is completely leveled out and the final tamp applied.

Basically it is moving the grounds to points that have "pockets" as you are lightly compressing...performing the distribution without all the other fuss.

For those who are scratching their heads after reading the above, here's a video:


From the Tamp and Dose Techniques Digest

PS: What's up with tapping the portafilter, Dave?

The motion on Dan's video is rather understated. Think of flipped coin that has landed on the ground, but not yet settled, as it wobbles along its edge.

You roll the tamper, so the top of the handle describes a circular motion above the basket. The bottom edge of the tamper presses down at one spot on the edge of the puck, and that spot rotates around the entire edge as the motion proceeds.

Here is a rough illustration:



When you are done, you've leveled the coffee, and sealed the edge of the puck. IMO, it's the fastest way to do this.

It is easier to to use a curved base tamper when doing this.

another_jim wrote:When you are done, you've leveled the coffee...

This is the key in my opinion, and this is why my motion is a very subtle one, as I said more akin to a simple rotation.

Clearly the motion being described, as I said, is not nutation, but in fact precession.

Um, if you say so.

But in actual mathematics, precession is 2D physics, the simple rotation of the axes of an elliptical orbit; while nutation is 3D analytical geometry, the motion of a tilted annulus touching a plane at one point and having its axis describe a circle parallel to that plane. This motion will inscribe a circle on said plane whose radius is the cosine of the tilt angle times the radius of the annulus.

I picked the word nutation, since that is the word for the motion I was describing. I never realized that it would give people trouble. If I had, I'd have called it the "coin flip tamp."

When I 'nutate', I first tamp the coffee in a straight down fashion to establish a fairly firm bed, then I gently press along the circumference in an effort to seal the edge.

I do not use the full weight of the tamper, rather a light touch. My goal is to prevent edge channeling without altering the even distribution (in theory) of grounds. Too much pressure will shift grounds/distribution.

After the nutation, I finish with a second straight tamp (and twist).

Once I began using this method, my pours became much longer, and I then had to adjust to a coarser grind. The espressos then became much better and more consistent. I believe this is largely due to a reduction in edge channeling.

• Baskets don't have an edge as shown above
• This whole 'seal the edge' strikes me as utter nonsense
• It's freaking near impossible with a close fit tamper

If the tamper is canted, it is not pressing the coffee at the basket side. As the tamper goes around the basket it is moving coffee away from the basket side.



A water molecule is around 0.2nm. The finest fines are, what, on the order of 1µm. If the puck were made of nothing but fines, there would still be space for 100's of water molecules side by side to slide between the basket and the coffee.

At best, nutation may work by shifting the coffee back and forth, filling some voids or 'locking' the coffee into the perforated bottom, as a line of defence against channeling.

A gentle side to side shake and light rap have equal or better efficacy.

drdna wrote:So in fact I am really doing an anti-nutating step, I guess.

Mathematical explanations and diagrams aside, I never gave nutating much of a chance, until I evaluated the Dalla Corte Mini. It was proving to be fussier about dose and distribution than expected. Jim suggested nutating tamp; it definitely improved the evenness of the extraction and lengthened the time before blonding. Intuitively I would expect it to make a bad situation worse, but in this particular case, it was an unmistakable improvement.

That said, nutating is not a regular part of my barista routine, though I do enjoy saying the word.

drdna wrote:Unless, I am wrong, most people are simply spinning or rotating the tamper while applying pressure.

I am doing a "wobbling" rotating tamp similar to the video, (after paying attention to this mornings shots, I edited this to show I am doing)less wobble maybe, but quite similar to the video. Just let it settle in, and check the level around the edges - making sure the tamper is level all way round compared to the edge of the portafilter, probably not even five pounds of pressure - this is on the Vivaldi.

An S1 vivaldi owner suggested that I use a nutating motion.I do have a convex base tamper for the Vivaldi. seems to give a more consistent distribution of the coffee in the PF, cuts down on spritzers, channeling.

I don't however do the nutation on the Cremina - flat based tamper, doesn't seem to need it.

ETA - I got the convex tamper because that was what Chris Coffee recommended for the Vivaldi. With the screw hanging down from the dispersion screen, I suspect that the convex base may benefit by distancing the puck from the screw. I also suspect that the "nutating" may work better with the convex base tamper.

Nutating the flat based tamper with the Cremina certainly is no improvement and may well be detrimental.

If were going ascribe a benefit to nutation over any another distribution, we should collect some data on basket geometry, tamper face diameter and profile, dose, etc. I don't think I can ever recall seeing a pro do it.

We've all had times when everything was pear-shaped and then miraculously ship-shape with no [conscious] change on our part. [ Or more often the reverse ] Ascribing a benefit when the result may have been self healing is witchcraft.

cafeIKE wrote:If the tamper is canted, it is not pressing the coffee at the basket side. As the tamper goes around the basket it is moving coffee away from the basket side.

That is so with a flat based tamper. Not so with a convex base.

another_jim wrote:It is easier to to use a curved base tamper when doing this.

I think the legendary Illy glass portafilter would be able to help with the geometry via direct observation.

Failing that, tamping into a transparent cylinder of the appropriate size might prove interesting.

My tampers are all flat and I haven't tried a nutating tamp, though I have used the Staub or NSEW tamp.

-Chris

cafeIKE wrote:If were going ascribe a benefit to nutation over any another distribution, we should collect some data on basket geometry, tamper face diameter and profile, dose, etc.

For those cases where it matters, I believe the difference is enough that any impartial observer/taster would not doubt the results. My guess is that this method will only benefit espresso machines that for whatever reason are prone to side-channeling as evidenced by "donut extractions" at the onset of the pour. Some espresso machines are like that. As I documented in Pressure profiles, preinfusion and the forgiveness factor, I accept that sometimes there aren't simple explanations why. *shrug*

Cafe Ike's diagram also presumes a basket with straight perpendicular sides, as opposed to a subtle slope. Sorry, but for whatever reason, it works for me....it isn't nonsense.

I don't need to collect a batch of data for an analysis. I just suggest to give it a try. Depending on your machine, basket, tamper, and technique, it might improve your shots. One size does not fit all.

SwingT wrote:That is so with a flat based tamper. Not so with a convex base.

Um...



A 57mm convex tamper with a 1mm rocker raises the center above the rim at about 4° and if this angle is exceeded, it's still moving coffee away from the edge of the basket. 4° is about 6mm displacement from the center on a 90mm tall tamper.

weasel wrote:Cafe Ike's diagram also presumes a basket with straight perpendicular sides, as opposed to a subtle slope.

The subtle slope on a basket wall is a degree or less. When the tamper is canted, the corner is moved away from the wall. It's quite difficult to maintain the downward force perpendicular to the basket bottom as the top of the tamper gyrates. If the force is not perpendicular, coffee is moved away from the wall, even if the tamper rim could be maintained in contact with the basket wall. Bye-bye 'seal.'

A properly shaped nutation tamper would have the sides cut back so the rim could maintain contact with the basket wall and compress the coffee there. An additional enhancement would have a spring loaded lip to roll around the basket rim to maintain symmetry. When the vertical tamp is applied, the lip would help maintain perpendicular tamp.

FWIW, I've seen some pros move the coffee back and forth with their hands on grossly updosed shots. Perhaps on updosed shots on some basket shapes, there is some benefit to moving the coffee back and forth to force coffee into the basket corner. If nutation accomplishes that, so be it. It may just as well be done by shaking, tapping before tamping, dental vibrator... but 'sealed edge' just doesn't hold water

weasel wrote:I just suggest to give it a try.

BTDT. Nutating with 57-58.5mm flat, C-Flat, 1mm & 2mm convex at a precision probably not considered by most proponents vs. K.I.S.S. show no improvement as has with every other 30#, tap, twirl and voodoo rain-dance.

HB wrote:I accept that sometimes there aren't simple explanations why

That's how we got Climategate, ignoring the science

I hate to argue Ian's ultra-precise reasoning about this form of tamping. After all, ground coffee has perfect geometric precision and transmits tamping force with the accuracy of a well-machined gun barrel.

So I won't dare to contend that a few pounds weight applied at a single contact point near the rim is more likely to close up any faults beneath it at the edge of the puck than 30, or even 100 pounds, applied to the whole tamper bottom. After all, in my ignorance, I thought that a powder would transmit force somewhat sloppily, so that the exact shape of the rim or basket edge or angle of attack would be irrelevant.

False assumptions don't equal science. '1 degree or less'? Hardly, my Rancilio basket has way more than 1 degree. Are all baskets the same? And you've measured them? What is your source for the 1 degree?

What Pro's do doesn't matter. Time is a major consideration for them. What machine are they using? Doubtless not my Silvia. Different techniques may work on different machines, etc. Is their way the only way? I'm sure it works best for their situation, not necessarily mine.....or others.

Voodoo rain dance? Bad analogy aside, it seems some very competent people here have found it useful. Is it possible they know something you don't Ian? I apologize for being personal.

Sincerely, please show a little respect for the opinions of others, even if you disagree.

weasel wrote:Sincerely, please show a little respect for the opinions of others, even if you disagree.

+1.

For what it's worth, whenever I read about this in the past, I chuckled about it's value (sorry Jim). It fundamentally seemed like a bad idea, plain and simple. That was my opinion until I ran across some espresso machines where it demonstrated a clear, unmistakable improvement. It doesn't surprise me that some, like Ian, say it's voodoo/poppycock/baloney because that was indeed my own experience with a wide range of equipment. Again, in my experience, the main benefactors are espresso machines with a propensity to side-channel.

For those following this thread, my recommendation is that the next time you see a "donut extraction", give it a try. If your espresso extractions are already orderly, I doubt you'll see an improvement in the cup. That said, apart from some of the snippy comments above, I'm glad Adrian raised the subject. This thread has piqued my curiosity and I will try to remember to retry it with less fussy equipment.

I'm still somewhat puzzled how nutating is supposed to waste time. I spend less than 3 seconds going from the loosely filled basket to ready to pull. I'm not aware of any faster method for distributing and leveling the puck; the various barista competition moves like stockfleth's or intelly chops, etc, are slower.