I'm trying to get a better understanding of this. Did a bit of a google search but couldn't find much for details. I noticed it was mentioned in the brewing of beer too but not sure if there is any relationship. Generally, I know it can happen from poor flavor development post start of 1st crack. Too fast in finishing a light roast. Assuming this would mean the outside is progressing more than the inside of the bean? In general I try to slow the progress of the roast about 10 degrees before first being careful not to stall the progress. What else should be understood or be done?
Ed

I can now stop roasts at 410F - 415F, halfway through the first crack, without grassiness. I need around three minutes from the time the first crack starts, but not more. The key for me is a proper drying of the bean below 300F. With that right, it seems I can go as light as I like.

I'm not sure how that translates to a drum, but my guess now would be to lower the drop in if the roast is grassy.

Jim
So your drying a bit more than you would with a med. or darker roast, by slightly extending the leg to 300f. I assume the goal being to have just enough moisture to develop the light roast but not so much as to limit/bog down the inner bean flavor development. Can I also assume that if you doing a darker roast you would do the opposite with the drying phase maintaining a bit more moisture to keep the roast from accelerating too much at the very end? I've noticed that it seems like light roasted grassy coffees seem to have a larger difference between external and ground Agtron readings. I must say that my roasts have really improved by the detailed discussions we've had on this forum! I'm getting a chance to do some roasting with a classic Gothot that should be interesting in comparing roaster dynamics with my hybrid.
Ed

I either add a minute to the drying time or cut the dose (more air per bean means faster drying). Never thought about dark roasts, but you're clearly right, keep as much of the moisture for as long as you can.

I can second Jim's observations on extending drying period.

In our bigger roaster, depending on bean type (and a gazillion other things) our drying period (to 300F or yellowing) will change between 3:30 and 8:00 minutes. The longer drying times are for softer beans (brazils specifically) and lighter roasts on medium to harder density beans.

Interesting thread. I've experience the grassiness as well over the years, and especially recently with my trying to bring out different character from my recent bach of Ethiopian Misto Valley. I thought I stalled the roast, so I was working to address it from that end.

What indications are you using to determine when the drying time is sufficient? Also, can you expound a bit on what about extending the drying time does to prevent the grassiness? I'm just trying ot build a better intuitive understanding of it all.

Chad
I'll try from what I understand. 1st crack is a moisture release. After that a certain amount of moisture is still needed to allow the rest of the chemical reactions to occur. Too much moisture will slow the process and too little will accelerate the roast. When lighter roasting, too much moisture will limit the roasting of the center of the bean and when dumped early the center will still basically be under roasted/raw giving the grassy taste. A little extra drying will allow the internal temp. of the bean to rise more easily giving a lighter roast more balance. I think adjustment in the drying phase is done with practice and experience. Jim or others might have some thoughts if anything can be monitored by the visible tanning or rates of bean temp. rise.
Ed

Thanks Ed, that's helpful and that makes sense. I'll give this some more thought and see if I can factor it into my profiles. I really like the character I get with a light Ethiopian.

The drop in and drying time calibration are hugely roaster specific. It might be seven or eight minutes in some unventilated drums, and two to three on some air roasters.

I started by getting all the beans fully bright yellow by the time I'd hit 300F. It took around 5 to 6 minutes for most beans. This turned out to be the big breakthough in roasting for me, I could get a non-grassy, sweet, well developed roast even at the classic New England, cinnamon, cupping roast llightness.

Since then, I've speeded up by about a minute on light roasts and two minutes on dark ones. This hasn't made the same huge difference of having a proper drying period, but it has improved the aroma a little and reduced astringency and ashiness on some of the more heat sensitive beans.

So, to beginners, I'd say start with the beans fully yellowed by 300F and then back off carefully. But the people posting here have already done all this, so they are in the tweaking phase, where it's all "local knowledge,'" i.e. learning the tricks of your specific setup.

Great thread.

I just had an espresso from SM ophiolite. My 3rd roast on the hottop B, and it was delicious. (exactly per SM description) Only reason for such a short curve really is the information on here.

First roasts were too grassy - the trick on the 3rd roast seems to have been cutting the heat after it hit first crack, to extend the time to second crack noticeably. Ran the fan on full all the way.

Obviously this is about darker roasts than the OP, but thought I'd throw it in as a data point