Interesting professional roasters' discussion - Page 4

#31: Post by **Frost** » August 26th, 2008, 11:41 pm

Alot of issues at work here to sort out & a couple I would like to get some discussion and opinion about concerning humidity and air flow. I have recently had problems with a fast light roast profile that went sour (and harsh) when humidity dropped below 18%. (side note on relative humidity, it seems we should be measuring dewpoint as absolute measure of moisture content(?)

Schenker discusses the effects of moisture in the heat transfer to the beans, and the advantage of re-circ roasters that retain moisture from the beans in the roaster. Air roasters that use fresh air will be more affected by changes in ambient humidity. I have assumed that the effect of lower humidity was only to reduce efficiency of heat transfer to the beans but I still suspect there may be more at work here.

Jim had mentioned about the management of moisture in the bean during the roast cycle, the competition for moisture in the various roast reactions and the importance of getting the right level of drying in the early roast while preserving enough for roast development by not taking too long a ramp to first crack.

The other issue that Schenker mentions that somewhat ties into the humidity/moisture issue concerns the use of air flow to bean mass and the problem of 'stripping' aromatics from the bean during the roast. (The discussion of the 'micro-environment' for the bean in the roaster ...some speculation on his part here too)

I am wondering if the moisture content in the roaster air flow would have a significant effect on the moisture retained by the bean for these chemical process later in the roast. I realize the 'free' moisture in the air is not available to the chemical processes, but that a too dry air flow would 'strip' too much moisture from the bean and inhibit optimum flavor development.

The issue of air flow is related.... But I have never adjusted that on my roaster (P1) until now that I have a MET probe in there, I am able to make adjustments and know the effect on temperature. ... So now have the second Variac on the fan control (Like Ed, I run with manual analog knobs to control the roaster and yes, it can be a handful to keep track! I don't have as many knobs as you Ed.)

My understanding is the air flow is a knob to adjust STE, heat transfer efficiency. (please correct if I'm mistaken) During the ramp phase and early heating, it would seem to maximise heat into the bean and minimise the ET, to keep the flow relatively high. As the beans approach (or enter) first crack, they need much less heat pumped into the bean to get from here to the completed roast, so dropping the air flow rate would make sense here ( during the final 'soak'). Also, as the bean temps rise into the roast phase, the volatiles are more mobile and likely to be stripped from the bean by the excess air flow. Slow the air flow here to create a better 'micro-environment' for the bean. (minding the humidity/moisture level during this phase as well.)

Obviously a 'fluid bed' roaster has limited ability to limit air flow as it depends on this for bean agitation... I'm already stirring for the first half the roast.... I will need to stir the second half, or maybe it's time to get some form of mechanical agitation.

Please feel free to poke holes in these ideas, I'm thinking of some experiments to run (some done and not yet tasted). I'm just thinking out loud here, Thanks.

#32: Post by **farmroast** » August 27th, 2008, 12:58 am

Frost
Was the first question I had to consider for design of my homebuilt. To go drum or fluidbed or something in between. Introduced air or closed system and what effects each might that have on the roast. As you mention, large amounts of introduced air on the beans would seem to cause negative effects. With my mostly closed system I get quite a bit of steam that comes out the sniff hole in the chaff canister. My thought/guess was some but not all moisture should leave the roast chamber. I've been ramping up the convection and agitation speeds till mid 300s BT then ramping down from there. Again, just another guess but seems to help keep the ET lower.
Hope to hear more science on this.
Ed

#33: Post by **another_jim** » August 27th, 2008, 2:40 am

I can't recall where, the Illy chapter maybe, but I did read that using recirculated air, varying humidity content, even CO2 and oxygen content, made no difference to the cup quality of a roast. Unfortunately, my chemistry never got the the moles and grams stage, so I have no idea what quantities of moisture are required in the air to make a difference in the roast.

I like the statement about airflow being a control on heat transfer efficiency. Again, my engineering knowledge on thsi is totally inadequate, but I think this too is nonlinear. If I do a 125 gram roast on my P1, I can use lower supply air temperatures for the same bean profile than on a 175 gram roast, even though i'm moving the beans at exactly the same speed. In any case, varying air speed, bean charge, even the degree of insulation would allow one to profile both environmentla temepratures and the bean profile.

But how would one use this perhaps excessive wealth of possibilities?

I've done cuppings for 535 MET versus 465 MET roasts and confirmed Staub's observations, the lower temperature was better for every coffee and brewing method (these happened to be the METs for my roast chamber uninsulated and insulated). However, I've made profile changes since I did this, and I've never done an exhaustive set of cuppings comparing, say, 480 to 450 MET, both for brewing versus espresso, or both for coffees that are fruity versus ones that are chocolatey, etc etc. It would be nice to be able to relate the reasonable range of MET temperatures one can use to changes in taste before sinking a lot into a dual profiling roasting system

#34: Post by **wookie** » August 27th, 2008, 3:32 am

another_jim wrote:I may be wrong, but it's hard to see this as anything except dealing with the coffee beans as a lowest common denominator raw material, then creating some brandable product from them.

I think that you are spot on. If one assumes that they view profit as a lot more important than roast quality, then it makes sense that they would be looking for ways to derive something drinkable from poor quality beans. In retrospect there were clues to this as well, such as emphasizing methylmercaptan ("fresh roast smell") levels. Still it was interesting enough that I will try the roast profile at least once. I did forget to include a link to the patent in case anyone cared to read more.

Here are quick summaries for two of the roast profiles for those who don't want to wade through the patent:

Example #5
1500 g of Brazil arabica was convection roasted. Environmental temperature set to 365F & 308 ACFM airflow. After 9 minutes, the bean mass temperature reaches 350F. The ET is then raised to 664F & 504 ACFM airlow for 1 minute at which time the bean mass temperature is 450F & the roast is ended with a water quench.

Example #6
1500 g of Brazil arabica was convection roasted. Environmental temperature set to 347F & 301 ACFM airflow. After 13 minutes, the bean mass temperature reaches 334F. The ET is then raised to 637F & 492 ACFM airflow for 1 minute at which time the bean mass temperature is 432F & the roast is ended with a water quench.

#35: Post by **farmroast** » August 27th, 2008, 10:02 am

another_jim wrote: But how would one use this perhaps excessive wealth of possibilities?

I've done cuppings for 535 MET versus 465 MET roasts and confirmed Staub's observations, the lower temperature was better for every coffee and brewing method (these happened to be the METs for my roast chamber uninsulated and insulated). However, I've made profile changes since I did this, and I've never done an exhaustive set of cuppings comparing, say, 480 to 450 MET, both for brewing versus espresso, or both for coffees that are fruity versus ones that are chocolatey, etc etc. It would be nice to be able to relate the reasonable range of MET temperatures one can use to changes in taste before sinking a lot into a dual profiling roasting system

These are the key questions. Can a fine degree of control in a dual profiling approach allow one to effect specific characteristics in the cup. I've been working on refining the measurement abilities of my controls to hopefully be able to test some of these possibilities. The measurement I don't presently have is environmental humidity which I guess would be possible but not sure the best way to measure it. I see these as most important with the emerging extreme quality coffees. Once you have a coffee that George Howell is satisfied with in terms of a clean cup(if that's possible

) How does one key on the best characteristics within the bean and could this be better achieved with a dual or tri profile system.

#36: Post by **Frost** » August 28th, 2008, 1:02 am

Some of the issues (& speculation) raised by Schenker concerning air to bean ratio, fliuid bed roasting, appear based on sensory (ie. taste) evaluation between his lab roasts and the industrial roasts (using the same green bean) I would say that there are other issues with his (isothermic) lab roasts unrelated to fluid bed roasting in general that are much more at issue here. These speculations may be based on good science but some bad data. (....for those who may skip ahead to the 'conclusion' section.... it is rare that I have heard a fluid bed roast described as 'bland, dull and flat') It should not be hard to approximate his lab results with a controlled air popper.

With a choice of higher air flow or higher MET, I will take the higher air flow every time. Everything I've tried is in agreement with your results Jim. (My finish MET is in this same range 460-465F Full City, and 445-450F for City range roasts. I have also insulated my P1 Chamber with a sandwich blanket of aluminum-fiberglass-aluminum) I don't have data yet but I suspect much lower ambient temps would cause these METs to be higher. Convection heating seems to be the best way to accomplish this low MET while quickly heating the beans. My thought on lowering air flow for the finish was to maintain the same finish MET. I can't think of much else to do with the fan control knob at this point: it would be to test for any noticable effect in stripping volitile aromas. Clearly, higher MET would have a negative effect here as well!

For the humidity issue, I have little hard data. I have a Davis weather station that logs weather data 24/7 for the last few years. I have paid no attention to humidity during roasting until I noted a bad batch that just happened on a day of extremely low humidity (dewpoint 5-10F). This was a bean that had been a consistent roast until then. I spent some time to see if there were any other roast dates that happened with such low humidity. In spite of fairly wide swings in relative humidity, it is rare for dewpoints to be outside a range of 35-60F. I have 2 suspect results that could be related to extremely low humidity. It may be a result that is only related to heat capacity, or has an extremely low threshold of extremely dry air but beyond that not much effect. At roast temperatures, the air has capacity to hold far more moisture than that carried by the ambient humidity so this dial has the potential to be turned up a long way.

#37: Post by **another_jim** » August 28th, 2008, 11:56 am

I once did a series of roasts where I either soaked the beans or put a shallow tray of water on the pottery disk of the P1 (below the roast chamber). This didn't work in terms of taste, giving the beans a fermented, hot dog stand taste. I'm guessing it over moistened the beans early in the roast. If there is any gain to raising moisture levels, it will need to be done with a lot more finesse.

#38: Post by **Frost** » August 28th, 2008, 12:16 pm

wookie wrote:.................
Here are quick summaries for two of the roast profiles for those who don't want to wade through the patent:

Example #5
1500 g of Brazil arabica was convection roasted. Environmental temperature set to 365F & 308 ACFM airflow. After 9 minutes, the bean mass temperature reaches 350F. The ET is then raised to 664F & 504 ACFM airlow for 1 minute at which time the bean mass temperature is 450F & the roast is ended with a water quench.

Example #6
1500 g of Brazil arabica was convection roasted. Environmental temperature set to 347F & 301 ACFM airflow. After 13 minutes, the bean mass temperature reaches 334F. The ET is then raised to 637F & 492 ACFM airflow for 1 minute at which time the bean mass temperature is 432F & the roast is ended with a water quench.

These profiles are interesting (to me) mostly because they are so extreme 'slow start fast (and hot!) finish'.
The time period from around start of first crack to finish seems immutable on my roaster. Do a series of roasts adjusting this time. (you can't go from 1 to 5 minutes here to the same degree of roast!, try 2-4 minutes or 1-3 etc..) Also interesting about moisture is the tremendous amount of water they dump into the roaster (over last 15-30 seconds) to 'quench' the roast. (edit: around 2oz/lb!)It makes a nice built in fire extinguisher should the need arise. Some of their profiles look to be hard to duplicate in a home roaster. (I'll get started on the water quencher right away!)

#39: Post by **rama** » May 23rd, 2010, 6:46 pm

Sorry to resurrect- this conversation is all new to me as I've been reading backwards through the H-B archives. Highly recommended thread for any others who may have missed it the first time around..

John P wrote:Jim,

when roasting Pacamara, charge your drum at 215-225F, and have a more gradual roast--about 6 degrees per minute on your bean temp-- until you hit first crack (375... give or take a few degrees) increase to about 9-10 degrees per minute (bean temp) after hitting first crack... level out your temp after about two minutes ....and you should finish in about 30 seconds to 1 1/2 minutes max after that.

Pacamara and Margogype are not as dense as your typical SHB and if you roast at the same rate as your typical roast the inside of the bean will overheat. This will kill a lot of the flavors.

6F/min from 225F to 375F means 25 minutes until first crack. And this produces drinkable results?

#40: Post by **endlesscycles** » May 24th, 2010, 3:04 pm

Absolutely, spending extended time in the low 300's will produce bland results. Going too fast will be lacking complexity as well. Roast, record, sample, repeat. Reiterate enough times and you'll spot hogwash when you see it.