Flawed Roaster Design?

[soliloquy]

I roast on a Roaster's Authority Victory 2 that I bought in January, used. It is a bench-top type roaster.

The problem I'm having is that the environmental temp never gets above 350 f during a roast, even when bean temp is over 400 f. During warm up, the ET and BT probes match up, which tells me there isn't a problem with the ET probe itself.

Maybe this isn't a problem, but I'm assuming it is, since many say that 70% of heat transfer during roasting is convection, and if my ET is lower than my BT no convection is happening.

The problem I believe is that the air going into the drum is not being heated sufficiently before entering. I've been told that air entering a Probat is heated over a 1000 f, because it is drawn across the flame bed. I've had the chance to poke around under the hood on a Probat and I noticed one major difference. The Probat's flame area is sealed off in a way. That is to say there is a metal plate under the burners. My machine does not have this, just open air down to the ground. Since there is nothing but open air under my burners, I believe the airflow entering the drum is not being directed over the flame bed and therefore is going into the drum at room temp.

Before I break out the welder and tack a plate under the burners, I thought I'd ask for opinions here first. Do most roasters have a more closed off burner area? Or is it typical to have it be wide open?

 

[peterjschmidt]

My Ambex is wide open.

Is it possible that you have too much airflow going through the drum?

Also, (I could be wrong) I believe the convection happening in the drum is simply referring to the air in the drum as the medium to transfer heat to the bean vs. direct conduction due to beans being contact with the drum. If that's the case then convection as you're using it, isn't dependent on airflow through the drum.

 

[soliloquy]

My Ambex is wide open.

Is it possible that you have too much airflow going through the drum?

Also, (I could be wrong) I believe the convection happening in the drum is simply referring to the air in the drum as the medium to transfer heat to the bean vs. direct conduction due to beans being contact with the drum. If that's the case then convection as you're using it, isn't dependent on airflow through the drum.

Good to know that your Ambex is wide open. I'll try giving her less fan power tomorrow and see how that goes.

If the air temp is lower than bean temp, the air will be stealing heat from the beans--cooling them--rather than contributing to an increase in temp. Therefore, the increase in bean temp I'm seeing beyond 350f is coming from the drum. Therefore, the drum is probably too hot, as it is fighting with relatively cool air in order to increase bean temp, which may be why I'm seeing as much tipping as I am.

Like I said, I'll try less fan tomorrow and report back. In the mean time, if anyone else has thoughts, feel free to let me know. Thanks.

 

[MillCityRoasters]

We need a profile and pics of your probe placements.

If your ET is exhaust temp, after passing through the bean mass, there's a point where BT and ET will appear to cross over. You could have too much air or your roaster may be operating normally. Are you producing good coffee? If yes, this is either a measurement or interpretation problem.

Iedit: just noticed you identified tipping. Something is too hot.

Call me today and I'll help you figure it out.

S.

 

[Amhas]

Tipping maybe to hot of a charge temperature, but a profile would help to see what you're dealing with. Here's a profile that shows I think what Steve is mentioning where BT and ET cross over. I'm using a IR1 and the burner is sealed to some extent but I'm haven't torn it apart to see exactly but the air must enter some place which would still be room temp.

 

[soliloquy]

Flawed roaster? More like operator error!

After a chat with Steve, which he approached more like an interrogation (in a good way; very thorough), I was determined I could rid my roasting of the evil defects recently plaguing it, such as tipping and uneven development.

I roasted several batches this afternoon. I was less heavy handed with the fan power, approaching each roast with far less airflow than I was used to. The result: no tipping what so ever, very even development from bean to bean, and my ET gauge was registering about 400f (compared to 350f before).

Tipping is something I have been struggling with. No signs of it with these roasts!

Also, uneven development from bean to bean (half the beans developed properly, 25% over developed, and 25% underdeveloped) was a real frustration. At times I cried myself to sleep. No. That's a lie. I was too caffeinated to sleep. I cried while I was awake. Mostly I cried while I was cupping. "How am I ruining these great coffees?" I wailed into the night. Dogs howled, mimicking me, absconding my sub par roasting skills. I heard one dog let out a bark that, I swear, sounded like, "your coffee is cupping below 80." Not even kidding. Even the dogs knew my coffee was bad.

Fingers crossed, I feel like I made a huge improvement in my roasting abilities today. And I owe it all to less air flow.

I blame all of this on the guy I bought the roaster from (I hope he's not active on here). He told me to always keep the fan on 100%, start with the damper 50/50 and go 100% drum by FC. Using this approach, I was sucking all the hot air out of the drum and having to go pretty heavy on the gas to make up for it. Now that I think about it, this method is a lot like what they do in Ethiopia with the skillet over the fire--all conduction and no convection. And that's kind of what my coffee was looking like when it came out of the roaster.

Thanks Steve! Thanks Peter! Thanks Amhas! But I think I got this from here. AKA problem solved. KNOCK ON WOOD!!!

 

[MillCityRoasters]

Totally hilarious post. I'm so Tweeting this url. Nice job! Persistence pays. Don't be a stranger.
S.