Determining the roast degree: Temperature or development time?

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
coffee_plXR

Postby coffee_plXR » Mar 15, 2019, 9:05 pm

Hi guys:)

I'm back with couple of great question marks on my mind.

March was a very special month for me because I could intensively experiment coffee roasting with many variables.
This definitely incurred me kilos of green beans to the trash bin, now I'm so much hesitating to find out what the reason was for spoiling the roast.

I strongly believe that there are many that have same questions as I do.

1. How SHOULD I determine the roast degree?

I recently started to doubt whether "drop temperature" REALLY says where we should drop out at a specific point.
Normally drop temperature is explained by temperature probe, but I now believe THAT number doesn't always identify the point of drop.

Since this probe sensing engages so much with surrounding environment, I often find out the roast color differs even on the same temperature based on bean structure, room temperature, charge temperature, roasting time, etc.
Its difference goes a lot more stiffer when I apply strong heat on it : roasting time goes shorter, but with that same indication, the beans are much underdeveloped., I guess that's because heat capacity differs in bean & probe material.

That means it does not fully represent the bean state.

The seriousness of this matter is, if I should still use temperature as my benchmark, how can I make it more meaningful?
How can I make beans well-roasted while leaving the temperature as good indication?

We all know that drying phase, mailliard reaction, caramelization, and development all run over temperature.
Then how can we make it more meaningful?

OR what else can be the dropping point?
Development time after 1st crack? bean color?


2. The cause of SPICINESS(STRONG CEDAR NOTES) and ASTRINGENCY.

My roasting was showing completely different aspect compared to last year.

No matter what I roast, it all gives me kind of strong cedar notes that stings my back throat.
I would forgive if it's affordable degree, but it's too strong. DP and WP coffees alike.

Green bean importer says it is due to old crop this season, especially Ethiopian bean.
But I don't think so since Columbia Supremo, Brazil Sul de Minas had the same aspect.

I also cannot understand because roasting surroundings were not so much different from last year.

In Seoul where I'm living, roasting was fairly great even when the weather was cold.
Now it becomes spring season, the result is rather worse than not.

I tried to apply more heat to fix this issue.
But it's like over-fermented(?) spiciness or feeling of oxidized(staled) spiciness and less tangy.
Anyhow this is just overly-processed spiciness, this is not a clear solution.

The thing is, I could merely find a thread explaining the root cause of this.

Some say on the other post, to grind a bit coarser or lower the water temperature, and my SMEG machine has 85'c for its highest....
Not like 98'c or 99'c. So it's already too low..

I did everything from
1. Idling after charge then turning on the gas
2. Gradually opening the damper till the end
3. Applying high and low charge temperature
4. making "temperature difference between ET & BT" larger or less

BUT NONE of these actually worked!


3. Good penetration of heat

Since I was studying which degree of heat I should prefer, I would like to know how to manage heat penetration.
- Too much heat can burn the bean, otherwise too much time can result in baking. less heat will cause under-development.

To be strict, how can I manage bean moisture to control heat penetration?
what is heat control point on each phases to best deliver the energy, with internal moisture playing its role?

User avatar
TomC
Team HB

Postby TomC » Mar 15, 2019, 10:00 pm

What kind of roaster are you using? Solid drum or perforated?

Can you share some photos of your green coffee you normally use? Is it Specialty Grade coffee?

What roast degree do you normally take your coffee to? End of first crack, (City, Full City) etc...

happycat

Postby happycat » Mar 15, 2019, 11:37 pm

Tom's questions are v important.

I can't think of a roast I would throw away.... if your roasts are that bad there is something puzzling going on.

Cedar and astringent ... are you hearing first crack? Do you let it run until the pops stop?
LMWDP #603

User avatar
another_jim
Team HB

Postby another_jim » Mar 15, 2019, 11:48 pm

Determining degree of roast is tough -- color, temeprature, time, or some combo of these? The industrial roasters who lose a container load of coffee if they screw up a roast use the ratio of two compounds in the roast gasses, one that increases over time, another that deecreases, to end the roast.

But there may be an easier solution to your problem -- I get astringent, cedery notes when I do light roast with a longish Maillard phase and where the ET gets too high after the first crack starts. That may happening with you when the weather gets warmer
Jim Schulman

coffee_plXR

Postby coffee_plXR » Mar 16, 2019, 10:07 pm

TomC wrote:What kind of roaster are you using? Solid drum or perforated?

Can you share some photos of your green coffee you normally use? Is it Specialty Grade coffee?

What roast degree do you normally take your coffee to? End of first crack, (City, Full City) etc...


A. I use solid drum roaster. It says 700g for its optimized charging size and I normally drop in 200g of coffee beans.
Image

B. Yesterday I roasted Medellin Supremo, degree between Medium ~ High
Image
The actual darkness is a bit darker than it shows. It was about +6'c from the 1st crack, took about a minute or half

C. Just in case I put drum shot, please comment if there's anything wrong with it.
Image


happycat wrote:Tom's questions are v important.

I can't think of a roast I would throw away.... if your roasts are that bad there is something puzzling going on.

Cedar and astringent ... are you hearing first crack? Do you let it run until the pops stop?


Yeah I was not too far from the first crack

another_jim wrote:Determining degree of roast is tough -- color, temeprature, time, or some combo of these? The industrial roasters who lose a container load of coffee if they screw up a roast use the ratio of two compounds in the roast gasses, one that increases over time, another that deecreases, to end the roast.

But there may be an easier solution to your problem -- I get astringent, cedery notes when I do light roast with a longish Maillard phase and where the ET gets too high after the first crack starts. That may happening with you when the weather gets warmer


Jim, What you mean by long Maillard phase?
I normally work around 2 ~ 3 minutes and that's my best. but hardly go over 3 minutes.

If that's the case, do I have to lower the heat overall and pick up during Maillard time?

User avatar
another_jim
Team HB

Postby another_jim » replying to coffee_plXR » Mar 16, 2019, 10:18 pm

It's what I call the part from the beans going yellow to the first crack starting, since you get Maillard browning but little caramelization.

If you don't measure the environmental temperature, your roasts will never be good. Just adjusting the heat while watching the bean temperature is a recipe for endlessly inconsistent roasts. It's like having an oven and operting the heat without knowing the oven temperature
Jim Schulman

coffee_plXR

Postby coffee_plXR » replying to another_jim » Mar 17, 2019, 4:57 am

I do check the environment evey time I roast.
But my point is, regardless of my control over heat and air, spiciness is omnipresent. can't exactly reveal why this is happening. Is this over-roasting or under-development?

Plus one more question Jim

Do you have any rule of thumb, to match heat and airflow especially for small roasters like mine?

User avatar
another_jim
Team HB

Postby another_jim » Mar 17, 2019, 12:06 pm

coffee_plXR wrote:Do you have any rule of thumb, to match heat and airflow especially for small roasters like mine?


Sadly, I think that's individual for every roasting device. I use the the Quest, and other users have different airflow to dial settings that I do. Bean and environmental probes are similar, they do not read identically even on the same roaster brand. You need to calbrate your own. But since you say you had the problem when the weather changed, ET seems the likeliest suspect.
Jim Schulman

edpiep

Postby edpiep » Mar 17, 2019, 3:02 pm

coffee_plXR wrote:But my point is, regardless of my control over heat and air, spiciness is omnipresent. can't exactly reveal why this is happening. Is this over-roasting or under-development?


Is this coffee you are currently roasting some that you have had for a while or some that you just switched to?" Your description of the coffee as "cedary" and "spicy" are strong indicators of old/stale coffee or coffee that has undergone molecular changes that affected quality (potentially moisture loss). I know you mentioned that all your coffees have the same taste so it could mean that they all are old or have undergone similar changes that affected their freshness...

Ryantheroaster

Postby Ryantheroaster » Mar 17, 2019, 6:43 pm

My qualifications for responding are about null, but I'll throw in my 2 cents.

It doesn't seem like bean color is a very good indication for when to drop a roast, as a roast at 6 min and a roast at 16 minutes can look the same.

More importantly, it seems like the development times and phases during the roast play a bigger part.

What does a typical roast look like for you? How long till yellowing/Dry end? How long until FC? What time do you usually drop your batches? What is your charge temp?