Sunday, August 26, 2007

   from AndyS

Why do espresso grinders suck? "Part Deux"


After two phone conversations with a certain well-known espresso engineer, a few things become clearer. I'm not going to use his name, because I may not be relating what he said accurately...but I'll do my best.

It may turn out that commercial grinders don't require special cooling mechanisms if they are carefully designed in the first place. According to The Engineer Who Shall Not Be Named, the grinding process actually heats coffee a lot hotter than the 85-90F that I measured. He says they've seen exit temperatures directly out of the burrs of at least 120F.

And he says that the main solution to the grinder heating problem is pretty simple: GET THOSE HOT GROUNDS OUT OF THE GRINDER IMMEDIATELY, WITHOUT LETTING THEM TOUCH ANYTHING: NOT CHAMBER, NOT SWEEPER, NOT CHUTE.

If you get the grounds out before they transfer a significant portion of their heat to the grinding chamber and chute, the burrs themselves don't get very hot. The grinder will stay much, much cooler. And a cooler grinder doesn't cook the lovingly roasted and stored beans that are waiting for their chance to be ground.

This minimum-contact coffee handling procedure becomes pretty easy with the straight path coffee grinders introduced by Versalab a while back and soon to be introduced by La Marzocco. So instead of flinging the grounds around an accumulation chamber and jamming them through a narrow chute, it looks like straight path designs are gonna become THE NEXT BIG THING.

Sunday, August 19, 2007

   from AndyS

Why do espresso grinders suck?

So I was visiting Ninth Street Espresso, and Ken Nye was telling me that all the equipment for his newest location had been selected, EXCEPT FOR THE ESPRESSO GRINDERS. And the reason the grinders were unselected was because (from the point of view of heat buildup in a high-volume location) the available grinders SUCK: they get so hot that the beans are literally cooked as they sit in the hopper waiting to be ground. In the ensuing discussion I inadvertently went into LECTURE MODE, and I hope poor Ken, Bob and Nick didn't get their minds blown with my impromptu blabbering on the thermodynamics of grinding coffee.

And now I'm thinking, there's probably four or five of you out there that are actually interested in this kind of stuff, so why not toss it out into cyberspace? And I'm hoping talking about this will hasten the day when grinders for high-volume locations DON'T suck.

Please note: I'm going to propose some numbers which are guesses or approximations. They may not be perfect, but they'll be close enough for our purposes. People who are allergic to math and to numbers can skip to the last paragraph (or more likely, skip this post entirely).

There are TWO sources of heat in an espresso grinder:
1. the electric motor, and
2. friction from the grinding process itself.

Electric motors are never perfectly efficient. Typically, for every unit of electrical energy you put in them, only 65-90% comes out as mechanical energy. The other 10-35% is wasted as heat. Particularly in shops that grind each shot to order, the constant start-stop-start-stop cycles make grinder motors particularly inefficient, probably hovering around 70%.

My Robur draws about 900 watts and grinds an 18 gram dose in about 3.5 seconds. Other grinders are similar in their energy consumption. For shops putting out one shot a minute during a morning rush, this corresponds to an average continuous current draw of about 52 watts.

That means the heat generated by the motor would be 30% x 52 watts = 16 watts, and the mechanical energy transferred to the grinding chamber would be 70% x 52 watts = 36 watts.

The kicker here is that the motor is only generating 30% of the heat. So various ingenious designs that cool only the motor are solving only 30% of the problem.

We can estimate that the 36 watts of average mechanical energy fed into the grinding chamber is used in several ways:
1. About 4 watts is absorbed by the coffee, heating it up 15-20 degrees F
2. About 3 watts is used to mechanically eject the coffee from the burrset
3. Perhaps 4 watts is used to overcome bearing, belt or gearbox friction.

This leaves an estimated 25 watts of mechanical energy that turns into heat through friction as the bean particles are dragged through the burrset and crushed against each other. This 25 watts heats up the burrs big time! It is the reason why, after a short time in a morning rush, the grinder adjustment dial on a grinder can be too hot to touch.

Here's an analogy for what's going on: have you ever burned yourself by grabbing an incandescent light bulb that had been on for a while? Well, if you somehow buried a 25 watt incandescent light bulb into your grinder's working parts, and left the bulb on for an hour or two, you can imagine that the grinder would end up getting REALLY HOT: 25 watts of continuous heat is a lot in an enclosed chamber. And this is pretty much what's going on inside the grinding chamber of any high-quality espresso grinder during a morning rush.

Of course grinder manufacturers know this, and try to arrange for convection or conduction to carry away some of the heat. But it's not enough. I hear that some folks have tried to use computer cooling systems to accomplish the same thing. Perhaps this approach will work out in the long run.

But the bottom line is, it's not enough to remove the electric motor's heat from your espresso grinder. In a high volume shop, you've got to find a way to remove heat directly from the grinding chamber. When we learn to do this, our grinder heating problem will finally be solved.

Sunday, August 05, 2007

   from AndyS

VIVE LA REVOLUCION!

About the WBC 2007 results:

First, big, big congratulations to Heather Perry. Your silver medal at the Worlds is a remarkable accomplishment. You should be very proud, and I hope your dad has stopped crying. :-)

In addition, Heather, I bought some of your Coffee Klatch USBC blend last month, and I thought it was simply great, one of the most delicious espresso coffees I tasted all year. You guys did a terrific job with it.

And now...James Hoffmann!

You really rocked the house, man. What a poised, natural, killer performance (thanks Katie and Zachary for the chance to see it)! And what truly blows my mind is how you WON THE WBC using Single Origin Coffees for your espressos and cappas.

At the 2003 SCAA Boston show I remember hearing a couple of bigwig SCAA lecturers stridently complain that the new-found popularity of espresso, with its emphasis on proprietary, unidentified blends, was RUINING the market for good estate coffees. Their point was not without merit, but it remained mostly unanswered at the time.

Soon after, some barista competitors (Billy Wilson and others) valiantly took up the challenge and did battle with various SO coffees.

But damn, you and your crew (Anette, Stephen, Jenny, and others I don't know) are obviously brilliant in selecting, roasting, and brewing your SO coffees. To win the World Championship with two SO espresso coffees is revolutionary, and my hat is off to you folks.

Vive la revolucion!

[edit] Peter Lynaugh (Terroir) reminds me that Troels won the 2005 WBC with their single origin espresso from Daterra. Apologies for my ignorance, and no slight intended towards any of the parties involved.

Friday, August 03, 2007

   from Nick

WBC 2007, Tokyo, Japan

By now, you've seen the amazing WBC 2007 coverage on zacharyzachary.com.
Stay tuned to Portafilter.net for the first play-by-play commentary on a WBC Finals video.  Each finalist, with PF.net color commentary by Jay Caragay and Nick Cho.  To be uploaded soon.