Real-time roasting by weight loss - Sweet Maria's prototype popper [VIDEO] - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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#11: Post by btreichel »

I'd say its crazy, But that is Tom (Thompson) Owens from S.M.; so I wouldn't discount it.

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#12: Post by rmongiovi »

Doesn't the weight loss depend on both the roast and the starting water content of the green beans? Without that starting point I'm not clear how a particular weight loss amount could guide a roast.

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#13: Post by baldheadracing (original poster) replying to rmongiovi »

There is no difference from how weight loss is used now; the difference is in addition to measuring weight loss post-roast, one can estimate weight loss during a roast, and thus use that estimate to assist determining when to drop.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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#14: Post by rmongiovi »

Determining when to drop seems fundamentally different from adjusting mid roast to me. The former is a decision about when to stop a roast whose parameters are based on other factors and the latter involves somehow translating a weight loss of X grams at a particular point in the roast into turn the heat up or down decisions. To do that wouldn't you have to know what amount of loss to expect for each phase of the roast and how that translates into the profile you're looking for? How do you know that?

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#15: Post by randytsuch »

Tried it over the weekend.

My SCTO weighs a little over 3kg, and I have a 5kg etekcity kitchen scale, ... 6640&psc=1

It also turn out the etekcity scale has the sensors in its feet, which I think makes it easier. And with the display off to the side, I can read it ok under the SCTO.

I had to make a big hole in a piece of wood, then I could put my SCTO on the wood, on the scale. The hole was for a big round bump in the bottom of the SCTO base.

First time, I messed up and tared after putting the beans in. You can't do this because at that point the weight will go down, and this scale doesn't go negative.

2nd time, put in 270g of beans, tared, added, and scale showed 269g, so pretty close.

This was a bean where I"ve had trouble hearing first, and couldn't hear it today.

So I aimed for 238g end of roast. Stopped at 238g, and final weight after roast was 232.2g.
Obviously lower than I wanted. Without the scale, maybe I would have stopped a little sooner.

2nd roast with scale, scale showed 270g at start, stopped at 239g and final weight was 231.9

Did a couple more roasts the next day. The first roast, after adding the beans the scale showed 250g after adding in 270g, so I didn't trust or use the weight.

2nd roast, it showed 273g. I ended this roast at 242, and final weight was 237.4g.

So I'm not sure why the Sunday data was different from Sat? Considering the resolution of the scale is grams, and I did some research into % error of load cells, and the one I looked at was a 0.05%. This sounds small, but its 1.65g at 3.3kg. SCTO+beans will be around 3.3kg. So that might be a factor here.

At my consumption rate, I don't need to roast again for a few weeks, so no more data for a while.
Next time, I may log weights as the roast progress. Maybe a delta weight from some point during the roast until I drop will give better results.
I also need to pay attention to how the ac power cords hang down, I think this is why I see the different starting weights.

But even though the data doesn't look as good as I had hoped, its very early, and I think this is worthwhile to help decide when to end a roast. I plan to use it as another tool to decide when to drop.


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#16: Post by mikelipino »

Thanks for doing the test! Interesting to say the least. Question on your trials, did you by chance notice if it were hot under the roaster by the scale? Load cells hate heat, they work by changes in tension and resistance at the top and bottom of the cell, and the tension will relax as they heat up. Since roasting is heat, this might be somewhat of a lost cause. Hoping for the best though!

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#17: Post by randytsuch replying to mikelipino »

Good point, but no, I didn't check.

I had hoped the wood block I added for spacing would also help isolate the roaster's heat from the scale, but I should check and see.
If I need to, I could either use thicker wood, or add some insulation to help keep the heat away from the scale.