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.
I have to believe that a grinder set up this way would still be transferring some heat to the surrounding areas ,no?
ReplyDeleteThermal conductivity of steel (burrs, and maybe shaft)) is roughly 46, Aluminum threaded housing a bit faster up around 250, and maybe some brass in there somewhere at about 109. Seems like heat will store up a little slower in the burrs, and transfer a little quicker throughout the chamber throat, which seems like the same end result- busy bar, and after a short while the hopper is slowly cooking the awaiting beans.
I'm just thinking out loud here, I say all this cuz' I was suprised to feel how hot the grounds coming out of the La Marzocco "S" were. I see this in my prototype 83mm conical grinder too, but I don't store the beans on the throat.
Anyway, it would be interesting to see a TC probe put just above the burrs in that LM grinder to see if it does heat up the beans, and if so how much?
Andy, maybe you know someone??
John, that's you, right?
ReplyDeleteI agree, it sure seems like a good straight through design would still still heat up significantly. So I made another call to Deep Throat, who just happens to work for La Marzocco. He repeated that the prototype "S" grinder did NOT get particularly hot, although it is still being worked on before it's ready for Prime Time.
You mentioned how surprised you were that the grounds were coming out hot from the "S". That's interesting for a couple reasons:
1. It shows that the LM approach is valid in the sense that every BTU of heat that comes out of the grinder in the form of hot grounds is a BTU that doesn't heat up the grinder itself
2. It suggests that traditional grinders producing cooler grounds do so mostly by absorbing heat into their structure.
I've put a TC into the grinder chute. Gets into the 100-110+*F range way too quickly, and it doesn't cool down for a long time.
ReplyDeleteAs mentioned, the grinder burr area doesn't dissipate heat away... it retains it. There needs to be a heat sink of some kind.
I am not convinced that the traditional grinder-doser system is as bad as people believe. "Deep Throat" knows very well that the direct-feed (grind directly into the portafilter) designs create their own problems. I'm interested in what they've come up with to overcome the "spray-distribution problem."
I'll take a Mazzer Robur with an active cooling mechanism, designed to maintain a good burr temperature while not overcooling the burrs, which would create condensation and possibly frost (if you go way overboard with the cooling).
That, or the simple addition of a heat sink to the bottom of the spinning burr carrier might mitigate much of the problem. The thermal conductivity of the burrs themselves would also need to be addressed, as Anonymous/"John that's you, right?" mentioned.
I'd also like to see a doser-design that is focused on good, consistent dosing; designed for the way that we, the grind-to-order baristas use them.
We use the dosers in a way they were never intended to be used. Fill the dosing chamber, and one or two pulls--that's the way those are supposed to be used. Our "flap-flap-flap!" isn't normal. There's gotta be a better doser design.
Maybe a grind doser/delivery system that actually integrates some "appropriate" amount of grind waste is the answer?
> I'll take a Mazzer Robur with an active cooling mechanism
ReplyDeleteSo will we all.
> I'd also like to see a doser-design that is focused on good, consistent
> dosing; designed for the way that we, the grind-to-order baristas use them.
I thought the Anfim was supposed to be this doser.
Quick question; is there actually any solid data out there that quantifies the effect of grinder heat in high volume locations? Has anyone actually set up two identical grinders side by side, used one for a few hours whilst letting the other sit and then done a few triangle tastings with 'spro pulled from both grinders?
ReplyDeletethis is an interesting discussion. when the first roburs came out i used to stick a big fan in the base and set it up to a thermostat, this usually meant a stable temp, if it got hot and and cold all the time the grind would wonder around like mad. we also used to machine the gearbox and burr housing to resemble an air cooled motorbike cylinder and head. lots of surface area to get rid of heat. wouldnt getting the coffee out asap as per the LM theory just mean hot ground coffee instead, would it not be better to use the burrs to remove the generated heat, in effect to maintain a stable temp on the coffee from bean to ground.
ReplyDeletehmm. justin
luca: I haven't seen any solid data. Like much of what goes on in coffee, in this case we just assume that the grinder heat adversely affects the beans waiting to be ground. Maybe we assume wrong....
ReplyDeletejustin: I believe the LM theory is that the hot ground coffee is immediately made into espresso, minimizing heat-related damage. This is supposed to be better than cooling the coffee by jamming (compacting) it through the grinding chamber and chute. Or at least that's the way I understand the theory.
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