Corretto Mk2!

[bassway]

Well my first corretto was starting to show signs of coming to its end.
Time to make another.

Another issue was I was getting an ash taste in some of my roasts. I couldnt nail why it was happening. It would happen at random and the carry through the next couple of roast. Tried cleaning it. No good.

Thoughts where:
1. That the bucket was too narrow and deep (Breville BB270)
2. Some chaff was landing on the heating element.
3. Chaff, bits of bean were getting stuck under the paddle and burning.
4. The PID was switching the whole of the heat gun off/on between first crack and SC. So maybe I wasnt getting enough air flow.

To fix problem 4 I thought I should get the PID to switch the HG and BM element but not the HG fan.

Got my hands on a Breville BBM100 and thought that this could fix problem 2 as the bucket was almost flush with the lid. It could also fix problem 1 as the bucket was longer and not as deep. The paddle seemed to be ok and would fix problem 3, if I didnt need to attach it to the shaft.

I pulled apart a heat gun that I had as a spare. The motor had a very simple AC to DC converter on it. On position two of the heat gun the output was 24V. On position one there is a diode that was chopping off one of the AC peaks therefore half the power to 12V. Simple.
So I found a 24V PSU lying around in the garage and connected to the HG fan.



With the fan on speed two all the time and the switch that allows the PID to control the HG element also switching on the fan motor it would protect against my stupidity.

How did the first roast go? BAD!
The BB270 is a metal chassis. The BBM100 plastic. It melted. Filled the garage with a toxic stench.

So I made a wooden box and a metal top. Stripped the BM for all the necessary parts. Doesnt really look like much of a BM any more!

Took a couple of roasts to get used to it.
The third and forth roasts went really well.
One of the issues is that with the fan on 2 but the element on 1 it ramp too slowly. Starts to level out at 120C.
With the element on 2 the ramp is too fast. But with the PID I can control it far more than I thought possible. I set it to 180C. It slows the roast, over shoots to about 190C and then holds there.
The control between FC and SC is very very good as well.

So the next mod will be trying to find a way to change the fan speed. Maybe two 12V power supplies in series and a switch to tap the middle.
Alas I am low on beans, so no experimenting. Come on pay day!!!

[Thundergod]

Re: Corretto Mk2!

That Taurus HG handle is great for mounting.

[bassway]

Re: Corretto Mk2!

Update.
So far so good. The roasts have no ash taste. One had a burnt roast taste but this was the very first roast and it was well into rolling second crack. Certainly not unpleasant like ash.

Havent done the HG fan mod yet but have put another element on. I used the element from my old BB270.
I have only done one roast with the second element so far.
The profile for this looks a lot better. The crack temps are a lot higher though. Prior I was getting FC at 200 - 205C. Now 215 -220.
The thermocouple is mounted on the bucket so heat from the bucket is transferred to the TC. One way it is bad, Im not getting as true bean temp as before. Then again I not sure this really matters if the crack times are the same all the time. At the end of the day you can never really get a true bean temperature measurement.

I am actually thinking that I might be able to have enough heat energy from the elements and then to have heat gun just as air flow. Find out what this "airflow" does to the roast that pro roasters talk about but dont tell anyone what it really does. But alas Im still low on beans so no experimenting yet.

[stuartgrant]

Re: Corretto Mk2!

This is great, Bassway! I enjoyed your old thread and felt like some of those observations confirmed a few things for me about getting the most out of a Corretto set up. Like, for example, that the airflow from a heat gun is liable to dry out the beans too quickly (and therefore unevenly) and cause tipping if you push the roast too hard.

So Im looking forward to hearing more about your experiments with this new Corretto. I think the 2nd heating element could be great! Of course, it could also cause big problems (eg. scorching, or lack of quick control over the roast...), but itll be interesting to find out.

Im very interested to hear any observation you can make (in the future) about the effect of air flow on flavours in the cup. And also % moisture loss - ie. is it necessarily proportional to air flow?

Anyway, good luck. Keep us updated!
Cheers
Stuart.

[Dimal]

Re: Corretto Mk2!

I think the 2nd heating element could be great! Of course, it could also cause big problems (eg. scorching, or lack of quick control over the roast...), but itll be interesting to find out.

I do too...

I reckon that if you could settle on an element output that supplied the Base Thermal Energy Input required, you could then use the Heatgun to supply the balance and therefore give you much better control over the finishing profile.

Regarding the Air Flow argument where heatguns are concerned... I dont believe this to be a big issue with regard to controlling bean moisture content. Ive never had any problems with my setup controlling moisture removal, eventually settling on a value of 14.5% - 15.0% mass reduction as providing the all-round best results in the cup for me. You can still do a lot of fiddling with a humble Corretto as is without having to resort to any additional complication in its operation.

It all comes down to horses for courses naturally enough and I still believe that a simple Corretto has an awful lot going for it and can be tuned to produce a wide ranging array of results in the cup (where it counts).... 8-)

Mal.

[bassway]

Re: Corretto Mk2!

Got some more beans!

So down to a bit of experimenting.

I tried three different roasts with the same bean (Wahgi Peaberry).

One with the element supplying as long as possible (low to no air flow)

One with both.

One with just the heat gun.

On all of the roasts I threw the beans in, turned on the elements and started to record at 50C. This is where I would turn off the element for the heatgun only.

First I did a roast with the idea of as little air flow as possible. The readings from this roast are high. This is because the TC is also reading the heat of the pan. I put the heat gun on at 10:30 226C as this was just before I was getting first crack on other roasts. Well first crack didnt happen till 12:30 237C.
Load 305gm unload 254.7gm.

Next roast - both heatgun and element.
I put the heatgun on at one minute on the low setting. At 221C 10:00 I put the heatgun on high. first crack happened at 232C.
Load 305gm unload 254.5gm.

The next roast I tried heatgun only.
I knew that first crack and SC temps would be lower but not this low!
185C first crack!
Too early at 08:00. I stretched out the SC to 16:00. This is where the PID rocks. You can hold the temp for a loooonnngg time.
Load 305gm unload 254.4gm.

So I tried again now that I knew what first crack, SC temp are for heatgun only.
Everything was going fine. I set the PID to start "braking" at 165C, slowly push up, waiting for first crack, waiting, waiting...... What the?
Ah well I push the temp up higher nothing. Then at 203C SC.
Load 305.1gm unload 254.7gm.

So what to learn?

The issue of no first crack. I have found in my last corretto if I held the temp high for a while prior to first crack the cracks would be far less and far quieter. Looking at the roast profile I am guessing this is what happened.

The end weight was basically the same. Air flow does nothing to moisture loss.

The was almost no tipping/scorching on any of the roasts so cant really comment on that.

Dont know what is found in the cup will say too much as the roast profile shape is different. Experiments with my last corretto found that ramp to first crack (shape) would/could make large differences in the cup. Usually a fast start ramp would create a "round" taste. Slow start then fast ramp would create a sharper taste. This is a very general statement. With some beans it made no difference.
I need to do that fan speed mod. Even then I dont know if I could match the roast curve.

Today I took the beans to work and put them through my syphon. Yeah, I know, only one day post roast.

Results:

Element only:
On the nose; Very strong vanilla and a bit a of cantaloupe smell. Very big and round.
On the tongue; Sharp hard acid - (like granny smith apple) - on the sides of the tongue progresses to the back. A nice acid though. Slight peanut taste. Sweet.
Very very very slight burn taste.
Vanilla remained as the coffee cooled.

Element and heatgun:
On the nose; Strong Vanilla, some apple and red grape. Round.
On the tongue; Sharp acid like lemon. Even less burn taste. Nutty and sweet.
As the coffee cooled the vanilla almost disappeared a low note perfume like red grape remained.

Heatgun only early first crack:
On the nose; Vanilla, floral rose, apple. Lost a lot of intensity. Smelt sweet?!?
On the tongue; Lighter acid only on the side of the tongue. Sweet nutty taste. Again less intense.

Heatgun only;
On the nose; Vanilla, not round. Very simple.
On the tongue; lest amount of acid.
As it cooled apple and rhubarb.

More to come!

[bassway]

Re: Corretto Mk2!

The next roast profile I have tried is to shut heat gun off (no air flow) a couple of minutes before first crack and switch back on a couple minutes after (roast profile not my idea).

The first thing I have noticed is that the roast seem more even. Both the Peru Ceju and Ethiopian Gambella which normally are very uneven now are slightly uneven. One would think that increased air flow means that more beans are getting the same amount heat so therefore a more even roast.
At a complete stab in the dark I would say at this point in the roast the beans are giving off there own heat and this might effect it some how. To be honest I have no idea why the roast is more even.

In the cup there seems to be more nut/chocolate flavours with beans like the Waghi and Nicaraguan COE. The 2009 Sumatra  has more berry and tastes cleaner, the berry more light and less "stewed".  

[WSullivan]

Re: Corretto Mk2!

update please bassway

[bassway]

Re: Corretto Mk2!

Well with most roasts ending up in others machines I though I would try a 500g (600g green) roast.

The result? Terrible.
Very uneven roast. Some beans got badly scorched. Some roasted light.

Looking at the agitation I could see that the beans at the top rarely got to the bottom. The beans at the bottom got burnt by the dual elements.

So while this corretto works really really well for 250g it cant do (unless I modify) a larger roast.

Maybe time to build a KKTO?

[WSullivan]

Re: Corretto Mk2!

Maybe time to build a KKTO?

You wont regret it mate, as long as your not as thick as i am and get the pot volume right ;D(which is easy!) youll be roasting 800gm at a time with perfect control, and evenly!!!!!

contact KK for a kit or......

http://coffeesnobs.com.au/YaBB.pl?num=1258419890

Best of luck mate

[Dimal]

Re: Corretto Mk2!

So while this corretto works really really well for 250g it cant do (unless I modify) a larger roast.

Maybe time to build a KKTO?

Thats where Ive discovered that the Dual Paddle design of the Breville Big Loaf BM seems to be an advantage with large-ish batches. As an experiment some time ago, I roasted a batch of 1.2Kg Green (normally roast batches of 750g these days) and it went as smooth as clockwork - and the end result was awesome in the cup.

I think all home built roasters have their limits (lower and upper) with the target being the best quality in the cup. With this Big Loaf, it easily managed the 1.2Kg batch size and could probably even go a bit larger if more thermal capacity was available but 300-350g is definitely its lower limit. It is even borderline at this really because sometimes it is really difficult to arrive at an ideal end result.

All I had to do to achieve the 1.2Kg roast was to fabricate a simple lid over the bread pan to contain the heat within the pan more efficiently and this was with a 1,600W heatgun too. It just goes to show what is possible with some very simple adjustments so dont give up on it just yet bassway....

Mal.

[lindsayra]

Re: Corretto Mk2!

Hi Bassway,

I have found your work on the comparison of BM element and HG air heating shared in this thread very valuable.
These results have made it quite clear to me that for the development of my current Corretto the next step should be to add a second element to the oven chamber, even if less than full heating is used (the simmerstat can take care of both elements).

Thank you very much for your excellent efforts.

Lindsay

[barrel]

Re: Corretto Mk2!

Great post Bassway.

A quick question for the guys running both the element and a heat gun.  

How do you go with current draw. Is anyone having trouble tripping breakers? or do you not have the heat gun and element running flat out at the same time?

What sought of current draw do the BM elements have?

[Yelta]

Re: Corretto Mk2!

So while this corretto works really really well for 250g it cant do (unless I modify) a larger roast.

For what its worth people, I modified a Breville single loaf bread maker about 6 months ago, my usual weekly roast is 625 grams the resulting roast is very even and I have total control.

My set up is a Bread maker, heating element and timer completely removed, drilled the paddle and shaft and secured it with a split pin (had the paddle jump off once)
The only heat source is a Bosch variable temp/fan speed heat gun.
Two thirds of the top is covered with a flame proof lid, a hole cut in it to accept the heat gun nozzle.
I use a temp data logger, hole drilled through side of BM shell and pan just above the paddle.
I cool the roasted beans in a bucket cooler using an exhaust fan and a large sieve.
During the roast I run a pedestal fan with the flow directed over the heat gun and BM.
My method is pretty straight forward,
Insert the data logger temp probe.
Beans in at room temp, anywhere between 14 and 40 degrees.
Start the BM.
Turn on HG usually set at 500 degrees (higher in winter lower in summer) fan speed 2, I usually drop the temp by about 50 degrees after FC.
At these settings I get to first crack (around 200 degrees) in about 12 to 13 mins.
I prefer a darker roast for most of my beans so take it to just past SC around 225 degrees, this takes approx another 5 mins for a total time of around 18 mins.
REMOVE TEMP PROBE and loaf tin then dump the beans into the cooler and agitate until cool, in my case approx 90 seconds.
Dont forget to wear work gloves when handling the hot bean container.
DONT FORGET REMOVE THE TEMP PROBE.

[lindsayra]

Re: Corretto Mk2!

A quick question for the guys running both the element and a heat gun.  

How do you go with current draw. Is anyone having trouble tripping breakers? or do you not have the heat gun and element running flat out at the same time?

What sought of current draw do the BM elements have?

Hi Barrel,

HG rated 1600W and maybe later 2000W

BM rated 470W    from the spec (Breville BB400)

If Ive got my conversions right:
9Amps = 2070Watts/230Volts
with this setup I am managing 833 to 1100 green grams in the preheated Corretto.
10.7Amps = 2470Watts/230Volts

Lindsay