But now I have decided to officially become a coffeegeek, and there is only one thing to do in order to become a true coffee geek, write you master thesis as a mechanical engineer about a coffee roaster of course!
I order to make the perfect roaster, I need help! And that's why I started this thread, I need all the ideas and as much feedback as I can get.
Perhaps there is something you are wondering about when it comes to roasting, and you would like an answer. Well, this is your chance! I going to spend 20 week on just one topic, coffee roasting! What is the biggest problem/drawback with coffee roasters today? Whats good, and what can be improved? What batch size should it cover, electrical, gas or both?
Depending on what i find out during my thesis, perhaps the perfect home roasting machine will be for sale in the future.
I'm thankful for every tip I can get, and will check in on this thread frequently
Posted Tue Nov 20, 2012, 11:51am Subject: Re: Taking home-roasting to the next level, need help!
PLEASE put a grill guard over the chain drive. An exposed drive like that is quite dangerous. Ever see what is left of a hand looks like after being mangled by a chain drive? The tryer needs a bit of work, and the addition of a counterweight to keep it upside down in the drum unless a sample is needed. Placing the beans on a white surface will give a better idea of color. No agitation arms in the cooling tray? It is why all cooling trays are round.
Posted Tue Nov 27, 2012, 8:53pm Subject: Re: Taking home-roasting to the next level, need help!
The kind of things that would peak my interest in a home roaster taken to the next level: Study the big pro commercial roasters and how they handle convection heating control.
Carefully designed air flow control that effectively gets the heat from the heating elements to the bean mass.
Controlled air flow that lets you maximize convection heating when you want it (during bulk heat ramp) like an air roaster, and minimize it when you want to coast through the finish, like a drum roaster. (both the Hottop and the Quest fall short in this measure)
Design the Drum with deep agitation fins that toss and tumble the beans, more aggresive agitation, for more even heating and better convection heat transfer. Maybe speed controlled to slow down when minimum convection is desired. (again; study how the big professional roasters do it, and shamelessly copy...)
If electric heating is used, careful design to maximize heater response, (minimum mass for this part, maybe nichrome elements). likely some method of direct re-circulating of heat or heat exchanger will be needed.)
Insulate the roaster not just to improve efficiency, but to reduce the temperature gradients within the bean mass and roaster.
Good process instrument and control for temperature and air flow.
Keep roast times within the ideal range for the designed batch size. (1lb max is fine for a home roaster)
I realize it will be a challenge to accomplish all this while keeping costs reasonable.
oldgearhead Senior Member Joined: 25 Jan 2010 Posts: 382 Location: Go Colts! Expertise: I like coffee
Grinder: Virtuoso by Baratza Drip: Chemex,Dilongi DCM900 Roaster: 1/2K Fluid-bed
Posted Wed Nov 28, 2012, 10:06am Subject: Re: Taking home-roasting to the next level, need help!
Frost here's a link to my $500, 120V, 500 gram, heat-recycling, stainless steel, fluid-bed roaster. It's made from an old air-pot brewer, a cocktail shaker, a heat gun element and a vacuum cleaner motor..
Posted Wed Nov 28, 2012, 5:54pm Subject: Re: Taking home-roasting to the next level, need help!
Thanks Jim, for the link. I remember following your project & build a while back. This is what we have to do to get what we want in a home roaster.
My ideal roaster would combine the benefit of both drum & air roaster, allowing full convection heating of an air roaster (for maximum ramp speed with minimum ET) and also be able to lower convection air flows when you don't want or need the heat transfer. (during finish when very little additional heat to the bean mass is needed) I'm a die hard air roaster, and have trained to get great results, but fluid bed requires the high air flow to agitate the beans for uniform heating even when you don't want or need that 100% convection heat transfer. I'm thinking mechanical bean agitation and full control of heated air flow volume through the bean mass. (I can accomplish this type of profile in my Poppery by turning way down on the air flow and stirring by hand,,, but yeah, that is a bit tiring; a carpal tunnel roaster if I roast too many batches) I'm way overdue to build my roaster. Too many other projects.
sversimo Senior Member Joined: 20 Jan 2010 Posts: 16 Location: Norway Expertise: I love coffee
Espresso: Izzo Vivi PID Grinder: Rancilio Rocky
Posted Fri Dec 7, 2012, 3:19am Subject: Re: Taking home-roasting to the next level, need help!
Thanks for all the great inputs!
Maybe two versions would be the best solution, that way I can make a high tech version!
There is probably something to learn from the professional roasters, but there is a huge difference between gas and electrical roasters.
I have thought about a smart way where basically all the warm parts of the machine works as a huge heat exchanger, preheating the air that will flow through the beans before they actually enters the machine. (where the air will be heated even more due to the airflow inside the machine) There are more than one advantages to this
- No hot parts that you can burn yourself on - Better efficiency - Ambient temperature less important - No water vapor or smoke will reenter the machine - Better ratio between convection heat and conduction
Also i need to reduce the thickness of the inner drum, its 3mm thick. Its great if you have enough time to pre-heat the drum, but time is money
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