Higher Delta BT

[nickthorpie]

Hey all,
I've switched from a solid to a perforated drum and I've yet to have a good chance to cup the two side by side.

The biggest difference I notice is how much lower my max DeltaBT is. On the Perf I can get it easily up to 40ºF/min, where as on the solid drum I struggle to break the 27º Mark.
I use a charge weight of 350g, and charge temp of around 400.

what do you do to get your dBT up higher? (What fan speed, should the vents at the bottom be opened or closed, etc)

[edtbjon]

Even though the perforated drum is a very different beast , the basic principles for roasting is the same. I.e. use low fan settings in the beginning of the roast.
Now, the airflow is the most "different" part in the two setups, so using "similar" air settings doesn't mean similar results. Just a little bit extra fan in the beginning will drastically change the efficiency of the burner. You just have to experiment a little bit.

[SusanJoM]

I have never paid any attention to the rate at which ROR begins to decline, so I am curious what the issue is. 

Why is 'higher delta BT' an objective?   Since it's a rate and not a temperature I don't quite get it.

[nickthorpie]

Hey Susan,
I roast through the constraints provided by Scott Rao's Roasting Philosophy. A focal point of this style of roasting is a constantly declining RoR. This presents a few challenges:
1. RoR can hit zero before you reach your desired development
2. Your roast can extend out much longer than you anticipate
3. It is much harder to hit your time targets for EoD and Fc.

These are all alleviated with a low turning point and high RoR at the start

I've included 2 pictures, one with the perf drum where I was able to get my RoR up high, and one with a low initial RoR.

High RoR: You can see pretty easily that I'm able to get a longer drying time, shorter maillard time, and a good long development while letting my AUC stay pretty low.
This was one of my favourite roasts I've enjoyed during a blind cup(The only one I enjoyed more than this one I forgot to save the graph )

Low RoR: Fortunately a higher TP than usual allowed me to keep my drying phase from extending long, but that was the only notable upside to this roast. You'll see that the mallard  phase extended very long as a result of the RoR being low; Fc Started 2 min later than I aim for, and I had to drop the roast before getting enough development in because my RoR ran out of room (I don't like it hitting less than 5, and it was about to hit rock bottom). This roast still cupped well, had some good tasting notes, but smelled a bit like honey nut Cheerios and was quite weak.

Thus is my quest to find a high RoR.

[nickthorpie]

Also: I just finished my 25th roast with this new Solid Drum, and I'm getting a better grasp of the higher RoR

I already knew that the speed of the fan has a direct and intense impact on the RoR curve (Fast fan= increased RoR).

So my current method is charge with the fan at about 25-33%, and as the RoR begins to rise, increase the fan along with it so that I set it to full right before it begins to flatten out.

[SusanJoM]

Okay.
I agree that the roast should ROR downwards, but it never occurred to me to manipulate it at the front end.
Very interesting point.

[Joey]

I recently learned about the "target" RoRs of 30/20/10 for each phase and noticed that a lot of my roasts were below target. In order to hit 30 on my perf drum I needed to up my initial fan speed a bit. I've started to use 45V-55V on my variac instead of my prior 25V setting. I drop down to 25V after about 3 minutes in order to keep things on track.

Attached a recent profile and definitely interested in learning more about these targets and how they affect flavors.

[edtbjon]

There's a lot in the subject title "Higher DeltaBT". First is how to achieve it and still be within a reasonable time frame with the various sections of the roast.
Since day one I've adhered to the Scott Rao "commandment" of a steadily dropping RoR, simply because it makes sense to me. When I started out with the Huky, there wern't much info on various approaches to how to control and adjust the roast profile with this roaster. (Now we have lots of discussions, approaches etc on this forum...) Anyhow, I usually tried to get a decent looking profile with a TP around 100C/212F, but this approach gave me rather quick drying times around the 4 minute mark. I also found myself using rather low power (burner) settings, so that the roast wouldn't run away from me. Another factor was me using a 30mBar regulator, which is the standard BBQ type cheap regulator here in Sweden. But, in short, my roasts were a bit hard to control and usually didn't taste that good either.
Next, after watching the MillCityRoasters video where Joe Marrocco demonstrates his Huky using no airflow during his startup and drying phase, I tried that approach and soon realized that I really needed more "uumph". I bought an adjustable prograde regulator and used it at around 50mBar, which gave better results, but still slow and just consuming more gas. I found out that even just a whiff of air would make the burner much more effective, so I made some more efforts to find a good "low air" setting which would make the burner effective without sucking all the moisture out of the beans prematurely.
The next step was when I started to charge lower, so that my TP would come at or even well below 80C/175F which really unlocked the whole roasting process for me. (A key element here is to realize that the length of drying process really is the least important mile stone of the roast. 4 or 6 minutes to DE doesn't make much difference in the cup (while e.g. a 60 seconds difference in the Maillard phase makes for a totally different cup...)) It was all of a sudden easy to get the burner really cooking and still be in control of the roast in all the phases, which kind of translates into "more energy to the beans". I.e I was able to have a little conductive heat in the beginning and could focus on more convective heat throughout the rest of the roast, without being punished by having to counteract on the conductive heat from a too hot roaster to begin with. The most important thing is that (at least I think) my coffee does taste very good.
I do feel pretty confident in being able to adjust my Maillard and development phases in say 15 seconds increments. I also feel confident in being able to replicate a roast, which is important. If I cannot replicate a roast, I will probably not be able to tweak it with control either.
So, to conclude, "Higher DeltaBT" was a key ingredient for my style of roasting, making it easy for me to be in the control of the roaster and produce good coffee.

Now... When are we to discuss AOC (Area Under Curve) ?

[nickthorpie]

Hey, that is super interesting that you don't find a difference between times in drying phase. In cupping I find greater sweetness in roasts with longer drying times, but less intense aroma.

Especially with the perforated drum, I find that the area under the curve is directly representative of the degree of roast. I like it because it allows me to consistently quantify how dark the beans are without eyeballing it. This lets me drop the beans at exactly 15°F•min every time, which in turn lets me compare more in depth differences between roast than just roast colour.

[edtbjon]

Hey, that is super interesting that you don't find a difference between times in drying phase. In cupping I find greater sweetness in roasts with longer drying times, but less intense aroma.

Especially with the perforated drum, I find that the area under the curve is directly representative of the degree of roast. I like it because it allows me to consistently quantify how dark the beans are without eyeballing it. This lets me drop the beans at exactly 15°F•min every time, which in turn lets me compare more in depth differences between roast than just roast colour.

Hmm I didn't say "don't find a difference". I was trying to say that the drying phase is the least significant part of the roast, as there's really no chemical processes going on. OTOH, I do build pressure in the beans during that part, so it's important that I get it right, giving it a good amount of energy.
A short drying phase usually indicates a high charge temp and unless I have very good control of the roaster, I find myself having to strangle the gas early on, using very little energy during most of the roast.

[nickthorpie]

Hey, that is super interesting that you don't find a difference between times in drying phase. In cupping I find greater sweetness in roasts with longer drying times, but less intense aroma.

Especially with the perforated drum, I find that the area under the curve is directly representative of the degree of roast. I like it because it allows me to consistently quantify how dark the beans are without eyeballing it. This lets me drop the beans at exactly 15°F•min every time, which in turn lets me compare more in depth differences between roast than just roast colour.

Hmm I didn't say "don't find a difference". I was trying to say that the drying phase is the least significant part of the roast, as there's really no chemical processes going on. OTOH, I do build pressure in the beans during that part, so it's important that I get it right, giving it a good amount of energy.
A short drying phase usually indicates a high charge temp and unless I have very good control of the roaster, I find myself having to strangle the gas early on, using very little energy during most of the roast.

Cool! I have read that drier beans going into maillard allows more of the reactions later down the roast to occur

[hankua]

Now... When are we to discuss AOC (Area Under Curve) ?

Quoted from Artisan Roasterscope Blogspot:

The AUC value of a roast profile as currently implemented in Artisan is not an absolute value, but depends on the given arguments for the start event and base temperature parameter. So only if those configurations are equal, the resulting AUC values can be compared between roast profiles.
If one selects a visual marker, like the yellow point (DRY) as start point and also to define the base temperature, the AUC readings should be comparable across machines, even if the probe of one machines generally reads lower than the other. This is because even if probes vary absolutely due their dimension or different placement, they often show a similar temperature increases.
While the AUC is for sure correlated with the total energy supplied to the beans, it cannot account for all those complex physics that are involved in the energy transfer during the roast. Time will show how useful this measure is to decide when to drop a roast or to improve consistency in roasting.