Titan Grinder Project - Page 30

by **gscace** on Sat Jan 26, 2008 5:14 pm

AndyS wrote:John, I'm not saying that temperature plays a major role in grind quality. But it is possible that, as Greg says, temperature plays a role in grind adjustment. And it is also possible that grind chamber temperature plays a role in drying out the partially ground dose that sits in the grinder between shots. Both of these mechanisms might help explain why the bigger grinders seem to need less frequent adjustments than the smaller grinders.

I think you'll agree that comparing the cutting surface length of conical grinders vs. planar grinders may explain differences in grind quality, but does not explain differences in grind repeatability.

Also, you make a good point that any inadvertent "heat treatment" in the grinder pales compared to what the coffee has already experienced in the roasting process. But in roasting, the beans are whole. There is a HUGE difference between what happens with whole beans (miniature pressure capsules) and with ground beans (finely subdivided with cellular structure partially destroyed). I bet if we compared the result of roasting whole beans vs finely ground green beans using the same input temperature profile, the differences would be profound. It is similar to the shelf life comparison of whole roasted beans (10-14 days) vs ground roasted beans (10-60 minutes?)

In the first instance I was talking about heat produced by burrsets. In the second instance I began to think about changes in ambient temperature possibley having an affect. Your quick little table is quite interesting. I'll have to look at it some more.

At the WBC machine trials, i had intended to install thermocouple probes just above the burrsets, just downstream of the burrsets, on the housings near the burrset adjustment threads, and one in the air nearby (ambient). I wanted to see how much things changed relative to ambient conditions when the grinders were used more or less heavily. Unfortunately we were so busy that I never got to do it. It would have been interesting to me because I think that thermal expansion of materials prolly plays a big part in stability of grinder adjustment, or lack of it.

-Greg

by **AndyS** on Sat Jan 26, 2008 5:42 pm

gscace wrote:Your quick little table is quite interesting. I'll have to look at it some more.

Uh-oh. I'm in trouble now. :-)

by **Matthew Brinski** on Sat Jan 26, 2008 9:12 pm

Andy,

I just got home and finally had a chance to look at your chart. I think I pretty much understand how everything correlates except the (sp ht). Is that the specific heat gain of the grind chamber? where does the 0.09 come from? I'm an idiot.

by **AndyS** on Sat Jan 26, 2008 9:23 pm

Matthew Brinski wrote:I just got home and finally had a chance to look at your chart. I think I pretty much understand how everything correlates except the (sp ht). Is that the specific heat gain of the grind chamber? where does the 0.09 come from?

0.09 is the approx. specific heat of brass. So it takes 0.09 btu to raise the temp of 1 lb of brass 1 degree F.

by **gscace** on Sun Jan 27, 2008 12:30 am

AndyS wrote:0.09 is the approx. specific heat of brass. So it takes 0.09 btu to raise the temp of 1 lb of brass 1 degree F.

It's prolly not the brass that is so interesting. It's the aluminum housings, which expand / contract much more with changes in temperature.

-Greg

by **AndyS** on Sun Jan 27, 2008 1:30 am

gscace wrote:It's prolly not the brass that is so interesting. It's the aluminum housings, which expand / contract much more with changes in temperature.

I just put in a bid on an eBay Handbook of Chemistry and Physics so I can look up specific heats and coefficients of expansion and all that stuff.

by **Nick** on Sun Jan 27, 2008 1:53 am

Andy, your recent posts in this thread make some sense, except for one thing: In a busy coffeebar setting Roburs get really hot too. REALLY hot!

But when they do heat up, they still don't require as much adjusting as a flat-burr grinder. For your theory to hold water, Roburs should, once they heat up, suffer from the same sort of symptoms... but they don't.

I still go back to a simple fact: Roburs grind coarser than Super Jollys. Look at the grinds. Feel them. It's right there.

by **Nick** on Sun Jan 27, 2008 1:56 am

gscace wrote:It's prolly not the brass that is so interesting. It's the aluminum housings, which expand / contract much more with changes in temperature.

But if it were indeed the aluminum burr carrier that was expanding and contracting, heat should cause the grinder to grind finer, as it heats up... which means you'd need to adjust it to grind coarser.

On a Robur, in my experience, once it heats up, you actually need to adjust it to grind finer to maintain flow rates. The obvious reason, which may or may not be true, is that the coffee is a little dry-er coming out of a hot burr set.

I really have a hard time believing that metal expansion has anything to do with anything.

by **AndyS** on Sun Jan 27, 2008 9:05 pm

Nick wrote:I still go back to a simple fact: Roburs grind coarser than Super Jollys. Look at the grinds. Feel them. It's right there.

Nick, if you adjust a Robur and an SJ to give approximately the same flow rate with the same coffee, it'll be easy to see that the Robur grind contains more coarse particles? That's really surprising to me, even given the results of John's laser particle-sizing experiment. His data seemed to indicate that the differences were real, but that they'd be very difficult to see with the naked eye (but not, perhaps, with the naked portafilter).

by **gscace** on Sun Jan 27, 2008 9:08 pm

Nick wrote:But if it were indeed the aluminum burr carrier that was expanding and contracting, heat should cause the grinder to grind finer, as it heats up... which means you'd need to adjust it to grind coarser.

On a Robur, in my experience, once it heats up, you actually need to adjust it to grind finer to maintain flow rates. The obvious reason, which may or may not be true, is that the coffee is a little dry-er coming out of a hot burr set.

I really have a hard time believing that metal expansion has anything to do with anything.

My thinking is that the housing grows more than the motor and motor shaft with increasing temperature, so the upper burr carrier moves away from the lower burr. Your observation supports that assumption.

-Greg


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