Titan Grinder Project: Does burr heating coffee grounds negatively affect taste of espresso? - Page 2

Grinders are one of the keys to exceptional espresso. Discuss them here.
User avatar
cannonfodder
Team HB

#11: Post by cannonfodder » Jun 09, 2007, 10:59 pm

I think it would be very safe to assume that there is more heat in the burrs than in the grind discharge chute. Friction generates heat and I am sure there is plenty of friction going on between those burrs. If someone has a way of actually measuring that, then by all means speak up. I am sure I am not the first guy to stick a thermocouple in a grinder to measure temperature.

While my statement may be incorrect (it has happened once or twice) it still stands based on my limited resources and results. Part of the reason we put most all of our data out in the forum is to generate discussion. I would be more than happy to have someone disprove me by taking the idea to the next level and doing more testing.

To date I think the project has been successful. A lot of questions have been raised and a lot of questions have been answered as we slowly move forward. How many times have you seen a coffee webpage use a scanning electron microscope and laser diffractometer in a review? That alone proves we are committed to the project, or we should just be committed. Not sure which quite yet.
Dave Stephens

User avatar
peacecup

#12: Post by peacecup » Jun 10, 2007, 1:01 am

One simple way to test for taste effects of increased temperature on grinds: grind enough beans for two shots, put one in an oven at 100 F for one minute (or whatever you suppose to be the maximum heat x time the grind might be exposed to in X grinder), then do a blind taste test between the heated and unheated. Repeat for sufficient replication. If this level of heat is not a problem, I can't imagine a few seconds in contact with burrs would be.

If one wanted to get a good idea of the maximum heat the grinds were exposed to they could grind beans for several minutes, then immediately measure the temperature of the burr surface.

Keep up the good work!

PC
LMWDP #049
Hand-ground, hand-pulled: "hands down.."

User avatar
RapidCoffee
Team HB

#13: Post by RapidCoffee » replying to peacecup » Jun 10, 2007, 2:32 am

Unfortunately this does not come close to replicating actual grinding conditions. It only takes ~10 seconds to grind a double shot on the SJ. The Kony takes longer but the temperature rise is slower.

At this point we really don't know how much heat the beans are exposed to during grinding, or how much flavor degradation occurs as a consequence. To date, I'm only aware of one significant temperature measurement: the 10F temperature rise measured by Dave during 10 seconds of grinding. This is not compelling evidence of degradation, especially when you consider that beans are subjected to temperatures of 450F during the roasting process.

When and if further data is brought forward, I'll be happy to revise my opinions on this subject.
John

User avatar
Jacob

#14: Post by Jacob » Jun 10, 2007, 6:16 am

cannonfodder wrote:I think it would be very safe to assume that there is more heat in the burrs than in the grind discharge chute. Friction generates heat and I am sure there is plenty of friction going on between those burrs. If someone has a way of actually measuring that, then by all means speak up. I am sure I am not the first guy to stick a thermocouple in a grinder to measure temperature.
FWIW:
Something like 8 weeks ago I bought an used single-phase Robur (labeled "Magister" :wink: ), installed a new set of burrs and put it into action.
4 or 5 weeks ago I would confirm I'm not having any heat issues at my 'home setting' so I emptied the hopper (grinding 6-7 singles in one go), removed the hopper and put my fingers down there where they do not belong. Air is a nice isolator so I expected any heat to be transferred from the burrs to the housing.
The burrs were more or less at room temperature (just as expected), but the air (just where the next shot of beans would sit) were surprisingly hot.
What happens could be that allot of the released heat from the grinding process ends up in the air, not the burrs?

When loading per shot I don't think we have any heat issues in a typical home setting, but the problem is that the robur makes the 'nicest' job then the hopper contains a fair amount of beans. My theory is that we need to look at means to replace the hot air in the throat with some fresh cool air before looking into ways of cooling down burrs.

User avatar
Walter

#15: Post by Walter » Jun 10, 2007, 6:38 am

RapidCoffee wrote:Do you believe the detrimental effect is caused by heating of the grinds? I doubt that a 10F rise in temperature (measured by Dave) has an impact on taste. But it's certainly possible that microenvironments created during grinding will subject the grinds to much more heat, enough to degrade volatile flavor components in the coffee. Any detrimental effect must be dramatic enough to operate within a very short time frame, since the beans are only in contact with the burrs for a few seconds. I'm not sure how you'd go about testing for this. Perhaps an IR thermometer?

EDIT: It occurs to me that there is a low-tech way to test for grinder-based heat degradation. Dave's temperature graph shows the grind temperature rising for the first 70 seconds. It's reasonable to assume that heat degradation, if present, gets worse with increased grinding time. Grind a hopper full of beans for at least a couple of minutes, dosing as you grind. Pull shots and see if you can taste any change between the extractions.
Yes, I do believe the detrimental effect is caused by heating of the grinds. In the "microenvironment" this heat must be due to two effects: friction and fraction. The former occurs in the later stage of the grinding and the latter in the earliest stage. But I would suppose - as an unproven supposition as Ken might call it - that fraction, meaning the breaking up of the cellular matrix after a heavy bending, has the even greater effect. Also I should like to think - another unproven supposition - that in the microenvironment, the local temperature gradient is at least one order of magnitude higher than the observed 10F.

An IR thermometer in a proper position might be able to throw some more light at the issue, maybe deep-freezing of the beans (i.e. with liquid nitrogen) and grinding in a non-humid - maybe eventually under protective atmosphere could contribute also to a little more insight.

But anyhow, Dave's method is measuring the environment temperature rather than the particle temperature as both air and grinds are pretty good thermal isolators. Trying to calculate the temperature within the particles from such a measurement appears nect to impossible to me. But it should be obvious that grinding the beans in an environment 10F hotter is an entirely different story...

Also the comparison with the roasting is somehow lacking, insofar as the chemical substances which seem mostly responsible for the particular taste of roasted coffee, namely caramellized sugars, Maillard derived aromas and other volatile or "sensitive" chemical substances are created in the last stage of the roasting process and their degradation begins immediately after the end of the roasting process. IMHO any form of grinding speeds up this degradation, but - alas, as Javaman rightfully hints at - we cannot brew the unground beans, and the best grinder is probably the one that has the least detrimental effect by internal heating (I'm still referring to microenvironments) while at the same time provides the particle size distribution which is best suited for making espresso.

User avatar
Jepy

#16: Post by Jepy » Jun 11, 2007, 10:39 am

Could it be that a small increase in temp when grinding a good thing? What I mean is, if we are trying to heat this up in the machine to a target temp anyway, this small amount may help it get there faster.
I know we've been hearing about the grinder heat problem for a while, and in the commercial environment I believe it's a bad thing, since the hopper is slowly cooking the waiting beans. Get the storage away from the burrs, and heat problem would no longer be an issue in the commercial application(in theory). I guess this would still depend somewhat on the retention in the exit chute

User avatar
jesawdy

#17: Post by jesawdy » Jun 11, 2007, 11:38 am

While we have no idea what happens to temperature "in the small", nor just how bad heating the beans in the grinder really is; the most important thing that I note from Dave's little experiment is not the temperature rise itself, but just how small the difference is between the Kony and Super Jolly.

My take away is that while heat may in fact be an issue, the difference between the Kony and Super Jolly is so small that heat generation alone would not account for taste differences when comparing the two grinders.
Jeff Sawdy

User avatar
RegulatorJohnson

#18: Post by RegulatorJohnson » Jun 11, 2007, 1:12 pm

IMO. IF preheating the beans by grinding them did affect it negatively, we would dose into cold baskets, and take other precautions to keep the beans as cool as possible before we put the ~200° water on them.

it seems like it would have to be a lot hotter than 94° to make a difference, like say a 200° PF basket, or 212° water.

i think the only difference it would probably could make a difference from heating would be that this extra heat would evaporate a bit of the water from the beans a bit quicker.

similar to grinding and leaving the beans for 45 minutes before you dose. they would dry out quicker then at a lower temp. but we dont let them sit. so i bet this evaporation is minimal as best. after a few minutes at 94° i bet there would be a detectable difference.

i think that heat from grinding is only going to accelerate the beans staling after the grind. this affects the cup. not the heat itself but the result of the extra heat, and the drier beans.

grinding before dosing is the way to combat this staling/drying after the grind. we already do this, yes? are we already using a solution?

jon
jon stovall
--
coffeetoolsapp.com

User avatar
danblev

#19: Post by danblev » Jun 11, 2007, 4:52 pm

Hi,
I want to take a different approach to particle magnitude and that is their mass. The particles from the bigger distribution group are 400-500 microns across. Also since they are very small the ratio between their mass and their circumference is very small or let's put it the other way around, they have a huge area for their mass. Also the great pictures that Rapid produced from the SEM show that they are quite porous and mostly irregular. Ignoring the irregularity and assuming that the particles are a true sphere and if my calculations are right then they weigh each about 5.5 micro-grams and have a ratio of surface area/weight of about 140.
Looking at the particle dimension, it looks that even if the particles get very hot they will ultimately cool down almost immediately.
On the larger scale, as the coffee is not ground in single particles but as a bunch, cooling down 20 grams of coffee is a different story but the pile starts after each particle has had a nice share of air to travel through so once it is a pile, then the heat loss rate is slowed quite a lot.
It is enough that the mass of the air that moved with the coffee grinds during the grind is large enough to keep the cooling going and reduce the heat of the grounds significantly.

A factor of the grinder that does affect the amount of heat generated during the beans shredding process is the speed of the burr or actually the speed of the edge of the burr that shreds the beans.
For instance, in metal cutting (e.g. with a lathe) the speed of the cutting knife against the metal is an important factor in the temperature that the cutting knife reaches during the cutting process. There, the temperature around the knifes' edge may be well above 300 C and the chips (even though they are much larger) cool down considerably very fast.
If bean grinding has any similarity (and I don't know that it does or doesn't) then the speed of the burrs does affect the cutting temperature and that may indeed affect the taste.
--
Danny

User avatar
matadero210

#20: Post by matadero210 » Aug 13, 2007, 10:01 pm

How about a very simple follow on:

1. Grind a dozen samples on the same grinder.
2. Expose each to 1min of some raised temp (a preheated oven or hotplate) (1 min chosen as a typical shot grind time--shorter may be more appropriate).
3. Taste the results for a variety of temps.

This has the advantage of constancy of grind.

raj
LMWDP 117