See, this is why I come here, fun and educational.

another_jim wrote:This may be true of drums, but not of convection roasters, where the profile is size independent. The larger drums do retard heat transfer.

Ken Fox wrote:What's the proof that large commercial drum roasters have a better roast product than smaller commercial drums? What is the dividing line between these larger and smaller commercial drum roasters? This quotation makes no sense to me and appears to lack any basis in fact.

My own overall limited observations are consistent with the concept of the effect of convection becoming more prominent as the ratio of the volumetric bean mass to conductive surface increases. Namely, the roast changes in a characteristic way as the bean mass increases. Thus, one way of controlling this in a small home roaster like the Behmor is to restrict the amount roasted per batch. This is one method I employ to good effect.

However, it runs counter to my presumption that a commercial drum unit would produce a better roast by virtue of its physical construction. If it is true that the larger drum roasters will function more by convection, air flow might become increasingly important as a means of regulating bean temperature. Now, I do this now by simply opening the door to my Behmor during the roast to vent the hot air, albeit being limited by the fact that this almost certainly alters the relationship between the ambient air temperature(which I measure) to the bean roast temperature.

The title of this thread was made tongue-in-cheek, and I came in with the presumption that commercial roasters are inherently superior machines, but having heard from those with more experience than I, it seems perhaps that one should not jump to this conclusion so fast, neither lusting for bigger, fancier roasters, nor scorning the humble home roaster. Perhaps the home roaster has the capacity to actually produce a roast equal to that of a commercial unit, and it is the lack of experience and skill on the part of the enthusiast upon which the onus of producing a good roast lies?

I strongly doubt larger drum roasters work more by conduction, rather the opposite. On sample roasters, BBQ drums, and small home roasters, the beans bounce lazily along the drum surface. In the big 25lb and plus drums, the beans buzz around airborne, like a swarm of hornets, bumping against one another a lot more than against the drum surface.

This seems to be a hard fact of simple geometry. If the air is not moving the beans, then the motive force that moves each bean has either been transmitted by the drum surface or by other beans. As the roaster's size increases, its ratio of interior volume to surface area increases as well. This means that the ratio of bean to bean versus bean to drum collisions also increases. Since as roasters get larger, the beans collide more with each other, the immediate heating source moves away from conduction transfer off the drum wall and towards convection transfer from the air and other beans. Can I say QED?

drdna wrote:My own overall limited observations are consistent with the concept of the effect of convection becoming more prominent as the ratio of the volumetric bean mass to conductive surface increases. If it is true that the larger drum roasters will function more by convection, air flow might become increasingly important as a means of regulating bean temperature.

Oh, good, so I guess we agree. Which unfortunately means I will probably need to work on my roasting technique rather than throwing money at the problem with fancy equipment. Frankly, that is not nearly as sexy, and smacks strongly of the whole "latte art" episode.

I think that the mass of the oven itself has a big effect on temperature stability and beam shock. For example, wood fired masonry ovens (several tons) give a huge spring to bread. Meanwhile if you cook bread in your kitchen oven, you have to open and close the door very fast and don't the same result.

the_deal_maker wrote:Have you ever heard of the Quest M3 roaster? A stainless steel alternative to the the HT from Taiwan.
I have one on order, having paid USD 970,00 incl. shipping via EMS to Germany.

garanti roasters, toper and has garanti companies, all offer 1kg roasters but since last year garanti roasters offering a new roaster called "garantti" which has 300gr capacity (as far as I know it's possible roasting less than 300gr) and for home use. I had asked its price when one of their manager visited our turkish coffee forum, he had said the price would be a little over $1000 (probably that price will be less for usa/canada though I'm not sure)

h: 50 cm
w:25 cm
d: 60 cm
weight:14 kg
heating: electric
voltage: 120x220x380 50hz




and this is their 1kg capacity garanti junior roaster gjk for comparison

h: 74 cm
w:50 cm
d: 40 cm
weight:50 kg
heating: lpg/ng
voltage: 120x220x380 50hz

drdna wrote:Oh, good, so I guess we agree. Which unfortunately means I will probably need to work on my roasting technique rather than throwing money at the problem with fancy equipment. Frankly, that is not nearly as sexy, and smacks strongly of the whole "latte art" episode.

Oops, sorry; brain fart. The idea that larger drums do more conductive heat transfer is a common misconception, and I completely misread your fiorst post. My apologies.

Understanding your roasters heat transfer abilities is key. As Jim mentioned,

I agree with them. If I were using a strange roaster for the first time, I'd run it so the environmental temperature ramps from 325 to 475 over about 8 to 10 minutes, and let the profile timing do whatever it wants.

ET and MET(and maximum bean roast chamber surface temps) has a lot to do with developing a profile. Matching a profile with ET is manipulated by batch size and considering heat transfer. Increasing convection will most easily increase profile headroom and batch size. For example with the Behmor, the drum speed is far from maxed out. Can't remember exactly but I think it's in the range of 12-15rpm. I exchanged the drive motor to about a 50rpm. This cut down the times for the same size batch with same heat profile by a couple minutes. This allows the choice of lowering the ET or increasing the batch size.
I too think that conduction is a small part of the total heat transfer in a large drum. But it is important to consider in the effects it can have on the roast. I saw some background wallpaper of roasted beans on a web site that showed a lot of speckled tipping. The ET in the drum may have been at an acceptable level but too much heat was needed to accomplish this making the drum surface too hot.