Roasting BT/ET temperature on Bella Taiwan Yang Chia 800n

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
ed63
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#1: Post by ed63 »

Hi all,
I have done about 10kg of roasting in 400gm batches and just started relaxing and looking around. I have stuck with the same Colombian beans from the same crop so I can gauge progress if any in my roasts. I believe the supplier has about 90kg left which will help but that's not the topic of today. The Bella has the Bt probe with pid readout and analogue dial for ET. I don't have any MET measurement device and not sure where to place it if I did. I have so far concentrated on getting to FC between 8:30 to 9:00 mins then something like 2:30 to 3mins for RD. I've maintained constant airflow and tweak the gas as she goes. Without knowing the MET I'm finding it difficult to do same back to back roasting. After I spill/dump/drop the roasted beans, I have to wait for the roaster to give the same reading on the BT and ET readouts, but that hasn't been reliable when the next batch is charged. The next roast never goes the same way. Is the BT /ET relationship supposed to mean something or do I need an MET measurement?

9Sbeans
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#2: Post by 9Sbeans »

Do you have roast logger (e.g. Artisan) graph?

I'm not a min-500 user, just some of general ideas about the small commercial solid drum roaster. Since you are in Australia, I'll use Celsius in the following paragraph.

I would suggest focusing on the BT first and don't worry about the MET. There should be a (machine specific) charging BT temperature and your charged bean mass relationship. Staying at 400gm per batch should be a good start (unless Hank and Henry has roaster specific advices, say 350gm?). Always preheat the roaster until BT @ 200*C, turn down (or turn off) the gas and charge the bean when BT @ 180*C. Turn up (or on) the gas [to scale A] 1-min after charging.

Observe the color of the bean. Note the time when it turns from green to pale white to yellow to tan to brown, and record the corresponding BT & time values. The [gas scale A] should let the green turn pale @ 4-min, and supposedly your BT should have 150*C readout. Find out the exact number of [scale A] on your machine. [Scale A] might be weather/bean depended, but it shouldn't deviate too much. This is the Dry phase. Try to target 4:00 to 4:30 Dry phase in your trials.

[Increase the gas to scale B] (And also [increase the damper for the airflow]) when the BT reaches 150*C. You should see both BT & ET increases in a higher rate again. Monitor the BT & ET. When BT reaches 185*C, ET surpasses 205*C, the beans turns tan, or the smell changes, turn down the gas to [scale C]. From the end of Dry to the first crack is usually called Ramp or Maillard (MAI) phase. Try to target 3:30 to 4:00 Ramp in your trials.

After the first crack starts, it really dependents on the types of beans and your own preferred roast levels. Very long time ago Henry suggested the targeted RoRs: 15C/min in Dry, 10C/min in Ramp, and 5C/min in Development phases based on his mini-500 roaster. It's sound advice. :)

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hankua
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#3: Post by hankua »

Using the same machine I can knock out repeatable roasts easily, starting from the second one. I'd say the machine is at full operational temperature roast 2-3. If the machine is outdoors, wind can be a factor; and affect the airflow thru the roaster/exhaust. You can use the torch or candle check on the tryer port and verify there is some negative air flow, even with the damper on "1".

Let's look at a for instance starting at the end of a roast; with the gas on 0.5kPa and air damper 3-5. When the BT returns to the target drop temperature say 180c the next batch gets charged at the same gas setting (0.5kPa) damper on "1". The ET will also naturally drop to the same @ temp. This can happen very quickly, especially if the damper is set on "5"; slower on "3".

Again, you've just dropped a batch in the cooling tray; when the BT hit the target bang, the next one charges.

If you follow this type of rhythm and make adjustments at regular intervals; 150c, 160c, 170c, etc, etc; the profile should follow the previous track. It's probably fair the say a majority of 800n users are not datalogging and roast with BT for the most part.

The dial ET is not as accurate as a digital probe, and it's location in the exhaust is not as good as one in the drum. Installing an MET thermocouple in the back plate should be very simple. My thinking on that is it would be probe #3 after the digital ET.

ed63 (original poster)
Posts: 55
Joined: 12 years ago

#4: Post by ed63 (original poster) »

With my airflow set to 3 and gas at about .55 I'm stabilizing the drum temp ( through the BT probe to 180°c for about 20mins before charging the beans. I leave settings as is for two mins and my turn around temp of 95°c generally happens at the 1:35 min mark. At 2min mark the gas is turned up to 2.5 and left there till the 6th minute where I turn down the gas to the 2.0 mark. Then again to 1.5 at 7 mins then 1.0 at 8 mins where it remains for the duration of the roast. The max ET of 180°c is recorded at 8 mins yet the BT continues to rise and I spill the beans ( no pun intended) at 218°c . once I spill the beans, the BT continues to rise above 220°c so I drop the gas to .5 and set air to Max till the temps begin to approach the original charge readings at which stage I set the airflow to 3 and wait for things to stabilize. The second roast will however go faster and I can't understand why. I roast inside my garage which has two doors. One is open the other is closed. I moved to the rear because of drafts near the front of the garage affecting temperatures. The result is a pretty good roast. My wife now drinks her latte with half a teaspoon of sugar where previously she would add two so I think I'm close to a good roast.

chang00
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#5: Post by chang00 »

To start first roast of the day, charge the temperature about 20 degrees higher, and gas setting 20mmAq higher. To warm up the roaster, keep the vent at 3-4 until the temperature is 160-180c, then close vent setting to 1. I generally roast 300g and 500g batches. I use 300g to gain more experience and variety.

Close the vent to 1. Charge the beans. Turn off gas. Turning point generally occurs at 1:30. Turn on gas again.

Some general rule of thumb. Consider two types of beans, the softer beans like Brazil, gesha, and dry processed Ethiopian. Then we have the harder SHB like Guatemata, Kenya, etc. For softer beans, start with gas setting 100mmAq for drying (until 150C), then ramp up at 150mmAq. For harder beans, 150mmAq then 180-200mmAq. Most coffee can be started with this profile for simplicity.

Vent setting wise, start at 1 until 150c, then 3.5-4 from 150c to 160c. You will notice with the vent open, rate of temperature rise is faster. Close the vent to 1 at 160c. Wait for first crack to occur around 188-192c. Open the vent to 3.5-4.

I emphasized over the years about gas roasters to find the "equilibrium" point. This is the point where the heat loss and input are about the same. Generally for the Mini 500/800N, it is at vent setting of 3.5-4 and gas setting of about 50-100mmAq with 300g load. This is the point you can really adjust and attenuate the rate of rise of temperature (BT). It is also important to clean the gas roaster periodically. Build up will really affect this equilibrium point.

You will notice I post with mmAq and centigrade. It is easier to remember settings without decimal point.

Another rule of thumb. Aim for 10c/min temperature rise before first crack, and 5c/min after first crack, if you like mellower taste with lower acidity. Or 15/10/5c per minute if you like the Western fast roast style. It is easier to use centigrade as it would be in multiples of 5 and 10's. After a while, you don't need to record nor use a data logger anymore.

As for vent setting. It is a way to rapidly change temperature, and the street thinking is too much air flow will blow away flavor. It is also a way to tune down acidity to shorten the time to drinkable coffee. The Kenya roasted light with the vent open will be drinkable on day 2-3, but will rapidly lose flavor by one week.

There you have it. This post summarizes my experience in the past few years on the MIni 500. Also be sure to check Patrick and Hank's tips.

ed63 (original poster)
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#6: Post by ed63 (original poster) »

Wow Dr Chang that's huge! Thanks for the heads up. It's interesting for me when reading people's posts trying to formulate something that can be applied in a scientific manner, but here it is. Thank you for sharing your years of experience and I will definitely be interested in following the instructions to find out how it tastes.
Cheers. I think Hankua is chasing down some probes which I will also be interested in acquiring. Not sure if my roasts will improve but I will be able to compare charts with others and possibly see where I may need changing.

ed63 (original poster)
Posts: 55
Joined: 12 years ago

#7: Post by ed63 (original poster) »

Ok so I had a try of your roasting tips today. From 160°C I had the gas on 209mmAq with the vent on 1 till first crack where I changed the vent to 4 and kept the gas as it was. Am I supposed to turn down the gas? The roast seemed to go too fast from onset of 1st crack.

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hankua
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#8: Post by hankua »

Here's a chart illustrating the general airflow settings on the 800n machine with the standard damper dial (1-5)

There is some air flow using #1, #2 is still relatively low. Both the heat and air settings work together, it's possible to use a fixed gas pressure and profile the roast only with air changes. The cast iron drum conducts heat and by reducing the air (convection), (conduction) increases. You can also reduce or increase drum speed during the roast as well to experiment with convection/conduction.

One way to tackle this is to leave the air on one setting and roast only using gas, then use a fixed gas setting and only use air for control; put the two together.

800n Air Flow Measurements
1-7%
1.5-10%
2-13%
2.5-26%
3-53%
3.5-66%
4-83%
4.5-93%
5-100%

Rilleys
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#9: Post by Rilleys »

Somehow for some reason i have trouble meeting the target temp for full city roast with the vent open especially during first crack with the vent open. The ET will fall below BT and will drag down the ROR considerably with a risk of stalling. If its for city roast i can get it with the open vent but i do get a more bittering experience though with the airflow open like for example orange acidity turns to lime. Do you guys have more differing experience with the current setup?

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hankua
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#10: Post by hankua »

If you mean open the vent as "all the way", I don't see any reason to do that except in preparation for drop. (Gas off/vent open) The 800n has two air control versions; the original with a damper and the upgraded precise air valve. Mine is the older version where the settings do not work in a linear pattern, the newer valve has a rotating slit/more proportational.

The lowest air setting I've ever used during 1C was "2", but will have to try "1" with a lower charge weight. The issue with the ET I think has to do with its placement outside the drum. Losing momentum during the roast development phase can be addressed by lowering the air setting, using more gas pressure during the roast, bumping up the gas at @180c temporarily, using a smaller charge weight.

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