Soak, Charge Temperature, and Gas at Charge

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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LBIespresso
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#1: Post by LBIespresso »

It seems that there are many ways to skin a cat and just as many ways to get to DE when roasting.

I have heard that the least important part of a roast is the first phase. Maye that is why there are so many approaches. I am asking my question (I'll get there) with the Cormorant or other nimble roasters (read, not a lot of thermal mass) in mind but it should apply to all roasters.

What do you more experienced people out there think about when picking your plan of attack with respect to charge temp, gas at charge, and soak time if you soak at all?

In my 200 or so roasts I have most recently been charging with gas at 10, charge temp of 360-390, and soaking for 1 minute then gas up to 42mbar.

Here's why I chose those:

The soak: Honestly, I think I do it because someone told me to try it and it should reduce the potential for some roast defects. But with my charge temp range and my diffuser closed (meaning flame not directly on the drum) I think that I could reduce or eliminate it.

Charge temp: Again, seems like a good place to start but don't ask me to defend my choice. I use the lower end for decaf and the Gesha from Dave B and I use the higher end for denser high grown coffees. I am washed only at this point. No naturals or honey yet.

Gas at charge: OK, here is where I have an opinion but I am far from stubborn. I charge at 10 because it makes it very easy to be consistent roast to roast. I feel like approaching charge temp is way more predictable with a lower gas setting especially with such a responsive roaster.

So now what? I think I will reduce soak to 30 seconds and see how it goes. Maybe ditch it all together after that. I am happy with my charge temps but ignorance is bliss. I think I will increase gas at charge to 25mbar and see how that goes.

So there you have it, the ramblings of a novice. My next roast is at least 4 or 5 days away so let's see what I learn from this thread.
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CarefreeBuzzBuzz

#2: Post by CarefreeBuzzBuzz »

A number of recent posts remind Cormorant users that their roaster doesn't have much thermal mass so skip the soak. Also you can try charging hotter and see what impact it has; faster time to DE but is that in a good range for you, and so long as there are no defect such as scorching or tipping?
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srosemer

#3: Post by srosemer »

IMHO, I don't consider the first phase as less important as it sets the stage for how I manage the entire roast cycle. That is, if I want to have a constant decreasing RoR, the maximum RoR I set at the early stages of the roast will really determine how much and how quickly I need to back off the power as you approach the end of the drying phase. On my first roast I generally soak my roaster at about 475 degree Fahrenheit at the bean probe with no beans in the hopper for a good 30 minutes, then bring the temperature down to my charge temperature for about 10 minutes before cutting the power and dropping the beans in. Then 30 seconds in, I apply power pretty aggressively ( up to 1 kPa NG for a 2.5 lb roast).

I've been experimenting with shorter roasts, with charge temperatures around 415 and targeting a RoR Max at ~20 degrees/30 sec (Fahrenheit), then start backing off the power starting at 5 minutes (and that's my target for end of drying phase). This approach provides enough momentum to manage a smooth decline in RoR without stalling the roasting during development (to avoid baking the beans).

All this being said, I don't have as many roasts under my belt as you and my roaster setup maybe different enough that any advice I'm giving may be of limited use (I'm using a 1.6 kg NG double-walled drum roaster).

Steve

Marcelnl
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#4: Post by Marcelnl »

I've posted it previously in a Huky oriented thread yet it indeed should apply to most low thermal mass drum roasters.
Now my drum is perforated, so not everything translates 1-1 to solid drums...

I preheat to 275'C (yes that is high yet in my case the BT probes measures direct IR to some extent so I do not expect it to reflect the actual temp)
after preheat (20min or so at 1KPa)
I charge with air at 30% (very arbitrarily chosen percentage as there is no scale or measurement, but it's found with the lighter trick) and gas at full blast, 4.5 Kpa.
No soak
Gas steady at 4.5Kpa until 3min 20sec
steady decreases of 0.5KPa every 30 or so seconds (I play a bit with the interval based on weather -at the start of the roast- and type of beans -at the end of the roast- but 30 sec is kept for most decreases)

This takes me to Dry end at around 4 minutes, First crack at around 7-8 min and to my target of dropping at around 207'C some 1:45 after FC, no tipping no scorching, no sourness, full bodied roasts.
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bshaw3852

#5: Post by bshaw3852 »

I was just thinking about the same thing on one of my last roast sessions (on a Cormorant as well).

I tried a couple of changes to see how things played out.

Here is the difference with 10 mbar or 25 mbar at the start of the roast, closed diffuser. As expected, at 25 mbar, DE and first crack occurred earlier. With cupping 6 days post roast I much preferred the second one at 25 mbar.





Here is the difference between closed and open diffuser. The open diffuser run went much faster and was took on heat much easier. The closed diffuser run tasted much better with cupping 6 days post roast, full Ethiopian flavor with tropical/berry fruit (I stopped it earlier though).


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mkane
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#6: Post by mkane »

Looking at the profiles I would use less gas after DE. This might let you spend more time in dev.and get rid of the crash.

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JohnB.
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#7: Post by JohnB. »

I played around with lower gas settings & soaks at charge but have found that I prefer the shorter roasts I get with my current (last 6 months?) methods. As I posted previously I use 25 mbar for preheat as Johan suggested. Take it up to 420°F BT, shut the gas off to cool & back on at 25 mBar around 360-370°F BT. Charge 454g at 380-390° & turn up the gas to 35-40 mBar depending on the bean & how fast I want to get through drying. Usually that's below 4:30. Fan is below 7 throughout the roast. Drum speed on 2/max. Diffuser open, I seldom close it. I've had zero issues with scorching & tipping using this method.
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LBIespresso (original poster)
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#8: Post by LBIespresso (original poster) »

JohnB. wrote:I played around with lower gas settings & soaks at charge but have found that I prefer the shorter roasts I get with my current (last 6 months?) methods. As I posted previously I use 25 mbar for preheat as Johan suggested. Take it up to 420°F BT, shut the gas off to cool & back on at 25 mBar around 360-370°F BT. Charge 454g at 380-390° & turn up the gas to 35-40 mBar depending on the bean & how fast I want to get through drying. Usually that's below 4:30. Fan is below 7 throughout the roast. Drum speed on 2/max. Diffuser open, I seldom close it. I've had zero issues with scorching & tipping using this method.
This looks like the plan I intend to follow. It took me a while to get there but that's pretty close to my next roast plan. Only major diff is I keep air at 8. For me the lighter test with an empty drum air at 7 was the same as a full drum and air at 8. Vent shape and length might explain our different settings though.
bshaw3852 wrote:
Here is the difference between closed and open diffuser. The open diffuser run went much faster and was took on heat much easier. The closed diffuser run tasted much better with cupping 6 days post roast, full Ethiopian flavor with tropical/berry fruit (I stopped it earlier though).
I too did a bunch of A/B testing a while back and got the same result. Now I only roast with the diffuser closed.
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