Whole Latte Love recently posted the following video concerning two identical Rocket machines with the only difference being the pump type. The conclusion (SPOILER ALERT, ha!) is that the rotary pump produces a better tasting, more consistent espresso. Judging by the comments, many are not sure this was a fair video.
Does anyone on here have experience with both types of pumps and care to comment on any variance in the taste in the cup? I had always thought the major difference between vibration and rotary was the noise level and ability to be plumbed in.

I think Jim S. and Ken Fox did a better comparison a while back.

Who ya gonna call? (vibe vs. rotary pumps)

No offense to WLL, but their informational videos are sincerely lacking credibility and support. Almost as much so as SCG (eek).

Thanks for the thread! Vibration machines have only gotten quieter since 2006. I'm 'new' to the espresso world (this year) but I'm learning as much as I can, quickly.

RyanJE wrote:
No offense to WLL, but their informational videos are sincerely lacking credibility and support. Almost as much so as SCG (eek).

You don't like Gail?

Zero. Zilch. Nada. Nix. In all these "debates" you have to ultimately ask "What's happening at the coffee/water interface?" Given 2 identical E-61 machines with the only difference being the pump type, I was never able to establish any sort of consistent difference. The water has a lot of travel before it meets the coffee, through the HX or dedicated boiler, then the gicleur and group. You'd be more likely to get taste variation with different showerscreens than different pumps.

Alan

I agree with Alan. It's like asking if you can taste the difference between a slow grind and a slightly faster grind. Nothing to see here.

The main difference the coffee sees is the ramp up in pressure; with rotary pumps ramping up a lot faster. On a manual E61, the dwell time will be a few seconds shorter (Dan switched between two pumps on the same machine about 8 years ago and observed this). Ken's pair of Juniors, one vibe and one rotary, were equipped with two different size gicleurs to compensate -- so we obviously could taste no difference. However Dan didn't taste anything obvious either. Ken and I didn't know about the ramp up difference at the time we experimented. If we had, we may have played mix and match with the gicleurs as well.

Looking at the recent investigations from people who can change dwell time with pressure profiling pumps, there is a subtle difference in the extraction, with longer dwell times increasing subsequent flow rates and extraction levels. Figuring out exactly how this affects the taste is another question; but all in all, with lighter roasts now the fashion, machine builders have been tuning or longer dwell times.

Has anyone considered installing a needle valve on the discharge line from the brew boiler to the group head on a DB/rotary machine?
One could easily adjust the flow rates and observe their effects.
Would be an easy install.
The one change I am still adapting to on my switch from a vibe pump/HX machine to a DB machine is the rapid pressure ramp up.

another_jim wrote:Looking at the recent investigations from people who can change dwell time with pressure profiling pumps, there is a subtle difference in the extraction, with longer dwell times increasing subsequent flow rates and extraction levels. Figuring out exactly how this affects the taste is another question; but all in all, with lighter roasts now the fashion, machine builders have been tuning or longer dwell times.

I agree that the effect on taste from manufacturers extending the dwell time, say with smaller flow restrictors, is subtle. Most likely the greatest benefit is to make the machine more forgiving of distribution flaws.

But the effect from very long and slow PI by using needle valves or variable speed gear pumps, and the much finer grind required, is often dramatic. I'm talking about 10-20 seconds or more for PI, which can allow grind settings that would otherwise choke the machine (on the order of 4-8 setting marks on my K10 and Monolith Flat.)

With a very light roast or a brew roast, the technique can make the difference between an undrinkable sour shot and a balanced shot. And for many coffees the flavors "pop" much more than with traditional extraction parameters. It's not like the subtle effects you get from using pressure profiling to slow down the ramp up pressure or introduce a slow ramp down at the end of the shot.

Yukonista wrote:Has anyone considered installing a needle valve on the discharge line from the brew boiler to the group head on a DB/rotary machine?
One could easily adjust the flow rates and observe their effects.
Would be an easy install.

Some of our members have installed needle valves for Slayer-like flow profiling, but putting them between the brew boiler and group head often isn't feasible due to the architecture of the machine.

For example, the group head on my GS/3 is welded to the brew boiler -- i.e., it's one piece. There's a tube inside the neck of the group that routes boiler water to the 3-way valve via a gicleur, which in turn routes the water to the puck. No way to insert a needle valve in there. It has to be added before the brew boiler, and even that can be a tricky modification depending the amount of room available.

And if you want to do more than experiment with flow rates, you need a way to bypass the needle valve -- usually a solenoid valve. That and the associated tubing and fittings, which have to withstand high pressure, can take up a lot of room that often isn't available in tightly packed single-group machines designed for home counters.