Forum > Roasting

Higher Delta BT

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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.

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