Burr grinder heat transfer?

[altoCalgary]

Thanks, Dan, for your thorough evaluation of these grinders. After reading your investigations, I bought the Mazzer E Mini B.

Since my purchase, I have ground on it about 100 pounds of light/medium roast beans. The Mini documentation suggests that little heat should be transferred to the grounds. Recently, out of curiosity, I placed a thermocouple probe in the front of the chute and ground about 9 grams that flowed around it. The probe heated up from 66.5 to 76 F in about a minute. (But, I was grinding for a lot less time than a minute!) Is this typical for a Mini E? If the burrs were worn, what would the rise in temperature be?

Ron

[HB]

A hundred pounds is a lot for Rocky, but the Mazzer's burrs will only be getting started. The Mazzer Mini's owner manual (link) says its burrs are good for 300 kilos and 400 for the Super Jolly, which has the same burr set at the Mini E. You've got three hundred pounds to go even with a conservative replacement at less than half their rated life. Nonetheless it's a good habit to carefully run your nail over the burrs when you're cleaning the grinder; you should replace them long before they lose their edge. Other wear indicators include coffee overheating and clumping, having to grind finer and finer, shot volume decreasing before blonding and grind time increasing.

Heat transfer is a serious problem for commercial grinders. The motor is directly below the burrs where heat has nowhere to go but up. The direct-drive motor also transfers heat to the burrs. Schomer wrote about his attempts to address the problem:

I located a belt driven grinder to eliminate motor heat from being conducted up the metal drive shaft into the burrs. To handle convected heat I fitted each grinder with a computer type silent running vent fan.

From On the Table #4

Your grinder has a big warning not to overdo it:


The rest time is for heat dissipation

If used as recommended, the heat transmitted to the grinds should be minimal.

[altoCalgary]

Thanks, Dan.

I unscrewed the hold-down ring (Wow, what easy access!) and ran my thumb nail over the burr edges. On most edges, I left behind a small bit of my nail. However, while doing this, I did notice some edges had nicks. I will be picking up a new burr set next weekend. It will be interesting to see if there is any noticeable difference between old and new burrs in terms of coffee heating and clumping, grind fineness, shot volume before blonding and grind time. I really appreciate your help.

Cheers,

Ron

[HB]

Interesting, would you post pictures of these nicks? I've heard of screws and other what-nots making their way into a grinder, but thankfully it's never happened to mine.

[altoCalgary]

Dan

Sorry this has taken so long. For a while, I felt like I was in my dentist's chair watching him take pictures of my tooth with a crack that he and I could both see, but did not come out in the insurance photo. Hopefully, you can see two small nicks, one shiny dot to the left of the screw and a larger, but fuzzier dot to the right of the screw head. Each are approximately in the middle of the grinder face. On the other hand, you may be feeling like my dental insurance company.

Ron

[cannonfodder]

Wow, that cutting edge is most definitely blunted. I wonder if someone smacked the edge with their driver while installing the screw. I also remember a rather lengthy thread about some questionable Mazzer burr sets making it to market some time ago.