Birth of the Bruce

[coffeelust]

Re: Birth of the Bruce

yeah, thatd be right. Race you to Mals place, Matt. Winner takes all!

Would be much better to use a Ceiling Fan Speed Controller for this as it is more suited to the inductive loading of the transformer. You will also need to fit a "Free-wheeling Diode" across the terminals of the wiper motor too as there will be some "Back EMF" to contend with that might create problems....

I asked the kid in Dick Smith if they had ceiling fan controllers (no) then asked if he could give me a free-wheeling diode. He looked at me like I was asking for a skyhook or a left-handed hammer. I didnt dare tell him it was to control my "back EMF"!

[matt_Hellyar]

Re: Birth of the Bruce

in his tool box

[coffeelust]

Re: Birth of the Bruce

nice one, Mal. Do you know where I might find those parts?

[Dimal]

Re: Birth of the Bruce

He suggested buying a light dimmer switch and attaching it to the power lead between the plug and the transformer.  Keen to give it a go when time permits.

Would be much better to use a Ceiling Fan Speed Controller for this as it is more suited to the inductive loading of the transformer. You will also need to fit a "Free-wheeling Diode" across the terminals of the wiper motor too as there will be some "Back EMF" to contend with that might create problems....

Mal.

[matt_Hellyar]

Re: Birth of the Bruce

hmm, that is very interesting, I might give that a try too.

[coffeelust]

Re: Birth of the Bruce

Hi Matt

havent roasted at all for a week or so; waiting for our demand to catch up with our supply. Well be roasting bigtime at the end of next week though - Christmas presents! Found a bean from Aceh Province called Tekongon that tastes suitably Christmassy. Our last roast in the Bruce was about 700g of that bean and it came out very even. We are getting a few fractures on the beans though. Is that bad? If so, is it avoidable?

Our last customers on the infamous helicopter day were a pair of veteran bikers. I told him I was interested in slowing down the rotation of the drum from 65rpm to about 45. He suggested buying a light dimmer switch and attaching it to the power lead between the plug and the transformer. Keen to give it a go when time permits.

[matt_Hellyar]

Re: Birth of the Bruce

whats the latest?

I did a 1kg roast in the drum of my new roaster with no housing around it and it was very uneven. I think I blasted it with a bit too much heat though.

I think that having housing helps the air heat to be even around all of the beans. my 750g roasts on current roaster are extremely even.

Id love to hear how your roasts have been going and what changes you might have made.

Matt

[coffeelust]

Re: Birth of the Bruce

Thanks for the advice guys. I just tried an 880g batch of Brazil and I think it was perhaps too big as the result was very uneven.  (Well still happily drink it though, hillbillies that we are  ) Will try somewhere in between next time.  We did put the lid down for a while but opened it when FC smelt imminent. Its all good fun. Next stop: 750g.

[matt_Hellyar]

Re: Birth of the Bruce

oh, I also jack the front of my roaster for bigger roasts, so they dont fall out the front. hasnt effected evenness of roast.

[matt_Hellyar]

Re: Birth of the Bruce

mine rotates at about that speed too, hasnt bean a problem. my drum is 170mm in diameter and I have three 25mm baffles.

I think perforating and enclosing the drum with the lid will help, also if you have an opening in the lid near your front hole you could set up some kind of exhaust, I have found that it helps a lot for temp control.

then all you need to do is mount a tc probe and roberts your fathers brother.

Matt

[Dimal]

Re: Birth of the Bruce

The Bruce does have a SS cover, which we have thus far not used.  If we did use that, I guess it would raise the temp al around the drum and perhaps mean that the beans being thrown around inside the drum would be roasted quicker.  Worth a shot?

That would be my first choice of things to try Luwaks....

This should provide a much more controllable environment and result in lower levels of heat input, in to the bargain. Would probably work even better if you could find a way to insulate the s/s cover.

I personally dont believe your drum is rotating too fast, looks to be roughly 60rpm and that should work out fine for the diameter of the drum youre using. If your beans are getting tossed around a little too much, you could look at reducing the dimensions of the lifter bars  a bit or conversely, raise the size of the roast batch. Youre basically looking for a rolling wave of beans that continuously collapses on itself. No reason why you cant play around with this using green beans and no heat.

For typical commercial roasters, they have the benefit of both heat and draught control which allows them to not only control the roast profiles to an infinite degree but to also roast very successfully over a relatively wide range of batch sizes. So, with a drum roaster restricted to conduction, convection and radiation as the only heat transfer options available, you either need to play with batch sizes to determine what the ideal size range is, or adjust the lifter bars height until you achieve the "rolling wave" phenomenon reliably.

Its all great fun though and very interesting.....

All the best,
Mal.

[coffeelust]

Re: Birth of the Bruce

Thanks AM, Ill think about what I can do. The Bruce does have a SS cover, which we have thus far not used. If we did use that, I guess it would raise the temp al around the drum and perhaps mean that the beans being thrown around inside the drum would be roasted quicker. Worth a shot?

Would perforating the drum make it any quicker?

Im just avoiding the more difficult options of slowing the rotation or relocating the burner.

[A_M]

Re: Birth of the Bruce

Our roasting times are quite long: 20-24 minutes versus the 12-18 minutes we were getting in the cast iron pot we had been using. Just wondering if this is normal/desirable, and if not, would perforations help.  I guess they would assist in the escape of smoke and the burning off of chaff.

From the video I saw... The rotation speed is somewhat faster than I expected and teh beans seem to get LOTS of movement and tossed into the air?

If you look at a HT.. The element is on one side - not the bottom, and the beans tend to sit; due to speed and gravity, on the bottom/ other side and under go a rolling motion....

Even very old mechanical ones with burners etc did not rotate that fast...

Not sure if you can slow it down, and manage tipping etc (Heat / Burner positioned at about 8:00) but my gut says that the speed is causing you heat loss. If you did slow it down and could roast a bit quicker... Also a saving on Gas

[coffeelust]

Re: Birth of the Bruce

Our roasting times are quite long: 20-24 minutes versus the 12-18 minutes we were getting in the cast iron pot we had been using. Just wondering if this is normal/desirable, and if not, would perforations help. I guess they would assist in the escape of smoke and the burning off of chaff.

[matt_Hellyar]

Re: Birth of the Bruce

I perforated the drum in my current roaster myself by wrapping some thin perforated metal that I found around my drum and using it as a drill guide. took a long time.
I dont know a lot about the difference between roasting perforated and non perforated though.