Coffee "zits"

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Coffee "zits"

Postby MDixon » Tue Jul 03, 2007 11:28 am

I was roasting some Mexican beans yesterday and at about the second crack mark the beans started popping circular "zits" off the back and sides of the beans. Anyone know what this is called and/or what causes it?

This is not the first time I have seen this phenomena, but it is the first time in a long time. The action of the pop was violent enough to send one of the small zits out of the BM and it landed on my back. Here's a picture of the beans and the zits...
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Postby cooldaddybeck » Tue Jul 03, 2007 3:32 pm

That means they are ready to be "refried"

(never seen it, so no real help from me)
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Postby MDixon » Tue Jul 03, 2007 5:00 pm

I've never kept roasting notes and we've tried probably 20-30 bean varieties over the years, but roasting a larger quantity brought it to mind. The amount of chaff on this batch was pretty low and the "zits" did not form with any vigor until around 2nd crack.

It almost has to be trapped moisture finding it's way out, but surely it has a name...Coffee Casey???
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Postby Bigbrews » Tue Jul 03, 2007 8:46 pm

That usually happens when the transistion from first crack to second crack happens too quickly. I used to have that happen all the time with the popper I started out with and then somewhat with the Cafe Rosto. I am now using the Gene Cafe and can control the transistion from first to second better and do not get the zits. With the Gene Cafe I am about 2.5 to 3 minutes from end of first crack to the start of second.

If you have a way to throttle your heat, try backing it down a bit as you get to the end of the first crack.

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Postby MDixon » Wed Jul 04, 2007 6:14 am

I noticed this morning in a commercial roasted whole bean -Rainforest from Costco - that some zits were in the package.

As fas as the picture above, I did not time it that closely, but was close to the profile of
390F-425F 2min
425F-445F 4min

Since 1st is around 400F and 2nd is around 445F and this has only happened occasionally in my roasting experience (maybe 2 or 3 times in 6 or 7 years) the explanation just doesn't seem to fit. It is something to do with 2nd crack for sure, but a few zits were visible at City roast. I'm thinking it is more of a bean phenomena than a procedural issue...
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Postby Bigbrews » Wed Jul 04, 2007 10:31 am

Do a Google search on Coffee Roast Divots" and judge for yourself.
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Postby MDixon » Wed Jul 04, 2007 12:59 pm

Thanks! At least I now know what they are called. Doing as was suggested and using google ended up with three basic schools of thought (in no order):
-Beans got too hot on the outside
-Beans heated up too quickly
-It simply happens with some beans and not with others

I did find a source that said they are caused by rapid outgassing which is entirely believable and probably the case. As far as too quickly, that wasn't the case here and too hot probably wasn't either since the air temp just above the beans was around 350F and the temp in the beans was spot on. In a few weeks I should be back to that bean again and it will be interesting to see if the phenomena is isolated to that bean as opposed to the other 3 I have been roasting lately.
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Postby Beach Brewer » Thu Jul 05, 2007 12:37 pm

I get the coffee roast divots on about 50% of all the bean varieties I've roasted. I've roasted about 12 variates so far. Anyway, I'm currently roasting Kona and Panama Boquete and am getting the divots on both. I actually was about to start a thread on this very topic but you beat me to it.

I'll try lowering the temperature of the 3rd stage in my IRoast2 and see if that helps prevent the divots. I did notice that the time between first crack and second crack was very short with the beans that divot so hopefully dialing down the temperature a little will solve the problem. I'll roast a batch later today and let you know how it went.
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Postby Beach Brewer » Fri Jul 06, 2007 3:19 pm

So I roasted a batch today that have previously given me lots of coffee bean divots. The only difference was I dropped the temperature of my third stage of roasting down 25F. Before dropping the temperature I'd say I was getting about 40% of the beans with divots. After dropping the temperature I got about 5% of beans with divots. I roasted both batches to the same roast, 10 seconds into 2nd crack. So it definitely made a difference to lower the temperature of the last stage. Next I will lower it even more and if that doesn't solve the problem I'll lower the 2nd roasting stage too.

I think bean divots are definitely caused by external bean temperature and it happens during 2nd crack. So my thinking is if the temperature is lowered enough before the bean reaches 2nd crack you won't be getting those divots.
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Postby MDixon » Thu Jul 12, 2007 1:17 pm

I roasted another variety this week and found about 4 shards of coffee that fell out as I shook the beans over the fan for cooling. These did not appear to be divots as in the pics. Since I didn't really change anything about the roasting methods it's starting to point toward a bean specific issue...I'll keep roasting and checking to be sure...
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Postby Bigbrews » Fri Jul 13, 2007 8:01 pm

Keep us informed on what you are able to determine. All I can relate to you is my results for the last six years of home roasting, most of those with high heat roasters ( poppers and Cafe Rosto). With those, a roast was usually about 8-12 minutes to second crack. Almost all of the second crack roasts had divots. With the Gene Cafe I now use, roast times are slower, 15-18 minutes to second crack. I have not experienced any divots with a slower roast. I must admit though, that I do not let the roast get to far into the second crack anymore. My tastes have changed and I tend to like the results better if the roast is stopped before second crack.

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Re: Coffee "zits"

Postby msav » Wed Jun 23, 2010 2:19 pm

I had the same problem with the divots. I found the problem to be the thermal cut off in my popcorn pumper. seems the element cutting out when it reached a certain temp and kicking back on again was causing this. Once I opened up the unit and removed the little metal disk out of the thermal cutoff device, I never saw another divot.

I have not other proof that this is what stooped the divots except that it has not happened again since I did the modification.

Mark
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Re: Coffee "zits"

Postby swede sd » Sat Jun 26, 2010 6:39 am

All beans are not dried down to the same moisture content. (close, but not the same) The beans with the higher moisture content will tend to "divit" more than those with lower moisture. As in popcorn, if the corn is dried down to far it will not pop as well as the corn with the correct moisture content. Its the moistued escaping that causes the explosion that makes the "zits". I have never noticed a problem with the taste of the beans that 'divit', so I just don't worry about it. In any case, the coffee you are roasting is so much better than the crap you buy at the grocery, that a few 'divits' just don't matter. Now the next question is, what is the correct moisture content for green coffee beans? I don't know the answer to that question, but I would guess it would be about the same as most feed grains. Just dry enough that it won't spoil in storage, but not so dry that it will reduce the weight too much. (its all sold by weight, the more it weighs in relation to its volume, the more its worth, dry it down too far, and the weight goes down, the weight goes down so does its worth).------------Roats on Dudes
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