popeye wrote:I also don't agree that drying time doesn't matter. My argument that it does is fairly simple: if you look how incredibly complex roasting coffee is, how can you say that the first five minutes don't matter?

Water does seem to be an incredibly important variable in coffee roasting.

You could say the first 5 minutes don't matter because no chemical changes are occurring during that period. If true, a drying period of, say, 3 minutes or 8 minutes should not affect taste assuming moisture content of the beans also doesn't change significantly. another_jim's proposed experiment to weigh beans at end of drying with different drying times seems like a good way to understand what is happening to moisture in the beans compared to drying time.

How does one separate out "drying time" from the total roast? Does one keep the profile afterwards the same? (i.e. a 3 minute dry and a 10 minute total roast turns into a 5 minute dry and a 12 minute total roast) or does one compensate to keep the total roast time the same (i.e. a 12 minute roast regardless of how long the dry time). In either case, it's impossible to break the roast down, correct?

what about the following experiment?
Charge your roaster. Roast until the beans hit 300 degrees. Dump and cool. Re-roast the same beans. If drying time doesn't matter at all, then the second roast should be identical to a "normal roast". If it matters somewhat, what is the longest the beans can be "pre-roasted" for without differing from a "normal roast." Is this a valid experiment?

Honestly, I haven't tried this. But it seems so impossible that the roast would not be affected that I have no desire to waste the beans. So, I'm open to hear how this experiment is invalid or that someone else has done this and the second roast came out normal?

In my opinion (which matters a lot to me, but rightfully very little to others) 30 seconds less drying time results in a significant increase in water (steam) available during first crack. This can often result in a stall as the ROR in my roaster can get down to 5-7 dpm instead of 8-10 where i like to keep it.

I understand that this can be conflated by other factors, notably that I roast with less airflow throughout the roast than i suspect many other people do. I like to keep the damper around 30-35% for most of the roast.

One final question. What causes the beans to turn yellow? Is that a chemical reaction (it would seem to be so). If it is, it does seem that different shades of yellow are achieved with different dry times. That would seem to be direct evidence that the chemical reactions the beans are undergoing are affected by how long the beans spend below 300 degrees.

popeye wrote: what about the following experiment?
Charge your roaster. Roast until the beans hit 300 degrees. Dump and cool. Re-roast the same beans. If drying time doesn't matter at all, then the second roast should be identical to a "normal roast". If it matters somewhat, what is the longest the beans can be "pre-roasted" for without differing from a "normal roast." Is this a valid experiment?

Honestly, I haven't tried this. But it seems so impossible that the roast would not be affected that I have no desire to waste the beans. So, I'm open to hear how this experiment is invalid or that someone else has done this and the second roast came out normal?

Double roasting is a thing that people have experimented with, myself included. I actually had very positive results with a washed Ethiopian coffee from the Roast & Learn a few months back. I had horrendous results with a Peruvian coffee.

Drying can affect the rest of the roast in two ways, off the top of my head:
(1) by affecting heat application; our heat supply is not infinite and the start of ramp / MAI is affected by the end of dry in terms of ET/MET
(2) Variance in moisture content affects pressure inside the bean (increased pressure reduces the rate of Maillard reactions, that's from Hoos' book); also variance in moisture content affects Maillard reactions.

popeye wrote: One final question. What causes the beans to turn yellow? Is that a chemical reaction (it would seem to be so). If it is, it does seem that different shades of yellow are achieved with different dry times. That would seem to be direct evidence that the chemical reactions the beans are undergoing are affected by how long the beans spend below 300 degrees.

Yellowing is caused by Maillard reactions.

popeye wrote:Charge your roaster. Roast until the beans hit 300 degrees. Dump the roast and cool. Are the beans the same? If you charge with the same beans, and roast, will the roast be "normal?"

Honestly, I haven't tried this. But it seems so impossible that the roast would not be affected that I have no desire to waste the beans. So, I'm open to hear how this argument is invalid or that someone else has done this and the second roast came out normal?

If I charge my roaster, roast until the beans reach 300F, dump the roast and cool, will the beans be different, chemically or in moisture content, if getting to 300F took X minutes vs Y minutes? I haven't tried it either. N3Roaster did (see video reference in #6 above), and did blind cupping to test whether a difference in taste could be detected. It wasn't. Clearly, if the difference between X minutes and Y minutes is large enough, even a lame palette like mine will detect the impact on taste. If the difference between X and Y is reasonably small (perhaps up to several minutes?), maybe not, at least, according to N3Roaster and Robert Hoos.

Interestingly, a few weeks ago, I did double-roast some beans (Panama Elida Estate Ntrl) to 300F, drop them (at 7:29), reheat the roaster to normal charge temperature and finish the roast. I did it when TomC proposed this experiment Roasting Experiments. The re-roast proceeded in a surprisingly normal manner. First crack was as vigorous as usual for this bean. The re-roast didn't taste much different from a normal roast of that bean with the same ramp and development time.

Dregs wrote:Interestingly, a few weeks ago, I did double-roast some beans (Panama Elida Estate Ntrl) to 300F, drop them (at 7:29), reheat the roaster to normal charge temperature and finish the roast. I did it when TomC proposed this experiment Roasting Experiments. The re-roast proceeded in a surprisingly normal manner. First crack was as vigorous as usual for this bean. The re-roast didn't taste much different from a normal roast of that bean with the same ramp and development time.

Alright, alright, I'll have to try it. But Panama Elida? You risked that coffee on an experiment? That's one of my all time favorites. You could even say its...bananas.

I thought I tasted bananas in that cup!

Panama Elida Estate Ntrl is one of my favorites, too. I used it for the roasting experiment because I know it so well. I was fairly confident the experiment would yield drinkable coffee at worst, and maybe something special at best.

"Though this be madness, yet there is method in't."

Of course drying time affects flavor, otherwise you would just charge at 600 and skip it. There is x amount of moisture in each bean, and you have to keep some of it so all the chemical reactions can happen, but not so much that it impedes the internals of the seed from roasting. And even if you wernt losing moisture in the drying phase(which you are), it wouldn't matter. Because you are setting up the Delta between the inside and outside of the bean, which will inherently affect the end delta(and of course the flavor). So yes, drying time absolutely affects flavor.

In January I had the pleasure of roasting for a few days with Joe at Cafe Imports. One thing he really tried to drill into my head was that, in regards to inner bean development, it's not just about the time it takes to get to 300, but more importantly how you get there.

For example, roast A blasts the heat in the beginning, high airflow; probe reads 300 at 5 min. Roast B puts on the heat more slowly, uses no fan; probe reads 300 at five minutes. Which roast will have more consistent development throughout the bean from outside to center? Joe would say roast B, and here's why: water is a conductor of heat. Roast B preserves that water, and uses it to drive heat to the center of the seed. On the other hand, roast A, with fast heat and fan, dries out the surface of the seed, and no longer has the help of water to act as a conductor and deliver the heat. Thus, while roast A may read 300 at 5min, it's a bit of a misnomer because it's only a measurement of the surface temp of that bean; the interior is likely well below that, and not yet "dry."

Another note about airflow and evaporation in the dry phase: using low to no fan during dry phase creates pressure in the drum; water boils at higher temps under higher pressure. Therefore, the longer you wait to turn on the fan, the more water you preserve in the seed, which you need.

I'm sure a lot of us already do this--wait about a minute after charge before applying heat, keep the fan low or off until near 300--but just thought I'd talk about it since it seems counter intuitive and might not be obvious to all home roasters. Also, this post is a super non scientific translation of what is actually going on inside a coffee seed during dry phase. Not meant to be definitive in any way.

Soliloquy wrote: Another note about airflow and evaporation in the dry phase: using low to no fan during dry phase creates pressure in the drum; water boils at higher temps under higher pressure. Therefore, the longer you wait to turn on the fan, the more water you preserve in the seed, which you need.

While I pretty much agree with everything you said, I have to take issue with the increased pressure claim, at least in the drum. Any pressure increase is likely just a more normal atmospheric pressure versus a very, very slight dip in pressure, but even that would quickly equilibrate in an unsealed environment . The system of a roaster isn't sealed. The gap in front of the drum to faceplate and rear is perforated. You can't build massive amounts of positive/negative pressure without containment or restriction (at least with the size and types of blowers we use in coffee roasting). I think it's more a matter of not stripping moisture out of the area around the beans by the fan drafting it away, as quickly. So the pressure gradient is more of the bean internals. If the moisture is too quickly pulled away from the bean surface, the heat transfer gradient drops. I'd have to crack open Hoos' book again, but I think he describes this pretty well, as does Joe Marocco in the excellent video.

PS, I'd love to hear your thoughts on your roaster! Share some pictures!

Hmm.... this sounds like theoretical coffee. Which is something I have a personal vendetta against. Ive run roasts that were as identical as I could get them with different fan settings(to test the whole more fan equals more drying). The results were the weight loss was the same on every roast. I have a feeling if I ran the same time and temp to 300 the beans would have the same amount of weight loss regardless of what the damper was set too. I do think more or less fan will adjust how deep the heat penetrates, but not how much moisture is lost.

....Turn on roaster to conduct said experiment.