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Using Propane for heat?
Wouldn't it be better to use a heat exchanger with propane fuel than direct induction like it seems everyone does?
I know propane is considered a clean burning fuel but it does have released by products. These by products have to be getting adsorbed by the beans as they are roasting. This would seem especially so in fluid bed roasters that use so much more fuel as compared to drum roasters.
For instance, fruit farmers do not run propane powered forklifts in there cold storage or concealed storage facilities because the ETHYLENE gas (a by product of burning propane) produced by the exhaust is very harmful and causes the fruits to ripen much quicker.

Now, I know it seems everybody seems to use direct induction, but I also wonder if that's not from economics more so than final flavor. Basically, in todays world, that all mighty dollar and maximum profits is the driving factor behind almost everything being produced and quality suffers in many cases because of that.

I know if/when I build a gas fired roaster, I will be trying a heat exchanger first and not direct injection, and it will have to prove itself a total waste before abandoning the idea.
Edited by BenKeith on 12/25/2016 8:25 AM
Propane gas is safe enough to use in all BBQ grills and home gas stoves & ovens. Why wouldn't it be safe enough to use to roast coffee beans?

"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
I didn't say nor was I insinuating it wasn't safe. I'm strictly referring to it from a flavor standpoint. Also, I'm just asking a question, not trying to stir the pot. I just feel with anything burning and emitting a by product has the possibility of affecting the flavors of anything it's in direct contract with, and coffee beans are definitely in direct contact since 100% of all emissions are going through them.
Edited by BenKeith on 12/25/2016 10:27 AM
Every article I read about whether propane adds taste to food states that it does not. The heat exchanger idea is neat however you may as well just do electric heating elements due to the inefficiencies involved with the propane heat exchanger idea. End result would be less expensive and easier to use and put together.

"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln
Good point.
I am sure at a minimum there is:
Not 100% combustion.
Other components in the fuel that are not burned up. (?)

How would you propose the burner be set up so the 'fumes' are not going through the roasting chamber?

Would a catalytic combuster achieve that? I have one on my wood stove to burn unburned gasses. It starts working at 500?F and I have seen it up to 1400?F (or more possibly).

Ken in NC
Backwoods Roaster
"I wish I could taste as well as I wish I could roast."

As Abraham Lincoln said "Do not trust everything you read on the internet".
I prefer electric, for several reason, much faster heat response, more efficient, cleaner and much less involved in installing it, but your average U.S. home roaster has limits to the amount of power available without some major upgrades. For instance, most homes have a max of 15 or 20 amps on their 120VAC outlets. You normally need to have a dedicated line run for a 240VAC and that usually requires an electrician, and hoping your service panel has room left to add a 30-60 amp additional 240VAC circuit and then getting it from the service panel to where you plan to roast. After installing a larger outlet, if you decide to move your roaster to another location, that dedicated outlet has to be moved also.

Propane doesn't create any of those problems. granted, design wise, it has obstacles to overcome, but has almost unlimited heating and mobility capabilities.

For the most part, once you go above needing more than 2,500 watts of heat in the U.S., it's just easier to consider gas.
Design wise, I would just do a radiator. The heat would be blowing on the inner core and the air would be passing over the outer section. The flame and exhaust would be isolated from the air stream so the two would never be mixed. Not a whole lot different than a home furnace, just maximize outer surface area to get max heat transfer.
I'm curious to know how developed ones palate would have to be, so as to determine the actual flavours (if any) the emissions impart and decide if they're a defect or not.
We do use things like charcoal grills which leave flavours on food we cook, and in my opinion enhance the taste of the food.

You could of course engineer a "clean" gas fired roaster but I imagine it would be a loss filled process on a small scale.

One approach could be to fire the exterior of the (solid) drum in a traditional way (gas burner with the flame contacting the drum and to use a heat exchanger with either heat recovery from the drum burner (air to air ones are large) and pass the resulting clean air through the interior of the drum.
I guess you could top up the heat recovery hot air with another burner to get the temperatures required or even better heat the drum interior air stream using electric power and use the gas power to the heavy lifting as it were. That way the amperage required should be much less and not require special wiring 😉
Hi Ben,
Based on my experience, the issue is more about design. Imparting off-flavors seems to be a non issue. Coffee is giving off vapor through the entire cycle. Pretty tough to absorb anything.. Cheers, Scott
I have a 30 amp 240VAC line run to my air compressor. I'm going to wind me a 6000W 240V electric heating element and just run me an outlet off that. I will see how many CFM of air I can push thru that and still maintain a heat range I want. I just have to not forget to turn the air compressor off so it doesn't try starting up in the middle of a roast. A 30 amp Circuit breaker probably wouldn't like a 22 amp motor trying to start while 25 amp heater is on.
Correct me if I'm wrong but LPG oxidizes to CO2 and H20 when burned. Water shouldn't impart any flavor.... after all the beans are giving off water while being roasted. While C02 does have a slight sour taste (think carbonation) again the beans are offgasing C02 anyway and continue to do so while resting.

Thoughts (including I screwed up my chemistry!)
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
Forgot the trace amount of Ethanethiol which would add minuscule amounts of S02
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
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