Why did second crack happen at a lower temperature?

#1: Post by **Joejoe** » October 19th, 2012, 1:13 am

I am working on roast profiles with my newly built corretto.

I did my first roast with a thermocouple temp probe, here is what happened.

Roasting 1lb of Ethiopian green

I wanted a slow drying so i figured out my rate of rise, it went just a little slower than I planned but in about 7 minutes the temp got to 300f or so and my beans where pale yellow, pretty perfect.

Then I cranked it up and got to first crack in 3:15 more and at a temp of 405f, and at 410f it started rolling and after 1:15 more and at 425f it stopped, now I was real happy, my set up was working perfect and was on a nice slow finish pace.

So then as I was shooting for a slow finish and had a nice steady slow rise and at 2 minutes after FC my probe said 445 and all of a sudden there was an increase in smoke and the beans were to rolling pretty fast into second crack. (it happened real quick, by the time I shut it down I was at 445 and was just at the beginning of rolling second crack) It was about 20 degrees lower than I thought according to sweet marias information.

So what happened, why did second crack happen at a lower temp?

October 19th, 2012, 8:18 am

2nd doesn't start at any specific temperature.

October 19th, 2012, 9:58 am

It does seem that there is a lot of variance even in information as to when second crack happens.

So the question is, are there any ways to predict when it will happen, like does it crack earlier on slow roasts and later on fast roasts or earier on soft beans and later on hard?

Also how does this effect the finished roast. If say Full City is 445f and at 445f you are starting rolling second crack is it full city or vienna?

#4: Post by **another_jim** » October 19th, 2012, 12:17 pm

The slower the roast, the lower the temperature of the second crack. You are hearing the breakdown of the bean's cellulose matrix, and this is a result of the total heat exposure, not just the current temperature.

In fast roasts, you will get a distinct gap between the end of the first crack and start of the second. the slower the roast, the more they will overlap. While a majority of people prefer faster roasts now; but there are still lots of roasters who do espresso slow enough to run the cracks together.

October 19th, 2012, 2:31 pm

Thanks, I tasted the roast and it rested less than 24 hours but it definitely has a vienna taste so I think I answered answer my question then.

According to wiki on coffee roasting my temps were right on the money. It seems like SM info was a little high compared to wiki and also compared to what I observed.

I am pretty excited over the level of control I am getting. Never thought I would be profiling roasts like this 2 two years ago when I started with my heat gun and a dog bowl. The coffee I am roasting now is SOOOOO much better. The corretto is amazing and i got a breadman that has a hour and a half continous knead cycle for 8.99 at goodwill (no hacking needed).