Probat L12- Help with tracking roast profiles

[midwestcoffee]

Good Afternoon,
This is my first post on the forums. There seems to be a lot of good information on the pages so hopefully someone will be able to assist us with our issue. I have a small coffee roastery that is doing fairly well but are having a few issues profiling. We are roasting on a Probat L-12 and up until this point, we have had a fairly straight forward roast profile that we would follow with each coffee dependent on its roast level: light, medium, dark, italian. Basically, we want to try to pinpoint profiles for each specific coffee to bring out the best characteristic of the variety, changing one variable at a time and testing on the outcome of the variable change. Today, we ran a few roast logs and as the roasting progressed the one thing we noticed was the end time of the roast were drastically different. Do we need to let it warm up longer? Thoughts on what we could do in order to make our roasting more consistent?

1/2 hour warm up. 400 degrees.
Drop temp: 420. Coffee: Mexican Chiapas. Medium Roast.
1st roast: 20:00
2nd roast: 18:30
3rd roast: 16:30

 

[snacksize]

midwestcoffee,

I have been roasting for a little over a year and I roast on a Probat L12 myself. The one thing that I could say to help with you consistency between your first few batches is let the roaster warm up for a little more time, or possibly more efficiently. My recommended practice for heating up my L12 is to heat it up to about 420, and the using the air control lever (lever on the right side of the drum if you're in front of the cooling tray) and find the sweet spot that will let your temp idle at 420. The temperature reading you're getting (assuming it is the same as mine) is located at the hopper. This temperature reading is not as accurate to what the actual temperature is. You are getting basically the hot air temp when really you want the drums thermal energy to rise. This is done (to my knowledge, which is still quite fresh) by reaching a higher internal temp, and letting your temp idle to warm up the very thick and heavy drum. The time which you let that idle will depend on the season (winter may be longer, summer may be shorter) and the temperature of the room. The batches at the end of the day have already roasted a dozen or so batches so the thermal energy at that time has built over several batches, the key to the first few batches is try to get the machine to act as though it has already done a dozen batches. Hope this helps!

 

[peterjschmidt]

Ditto what snacksize wrote; it looks like it wasn't fully warmed up, that's all.

Also, you can set up your roasting schedule by batch size and roast level.

Today I was doing a batch of Harrar that was 30% smaller than my typical batch, so I did that one first. I also tend to schedule the first batch for beans that will either be roasted lighter or beans that like a gentler profile, like a Brazil or other low-grown bean.

My roaster has a digital controller that will turn off the gas at a set temp, so I'll set it for 420 and let it get up to that temp and let the flames cycle off and on at least a few times if my first batch doesn't fall into the above categories and will be a typical roast.

 

[chast]

agreed with all of the above. The RTD/TC is at the bottom just over the flame and just because the controller says it is at the correct temp it really isn't. I wait until I cannot touch any part of the top of my roaster then I drop the beans, usually around 400/420. Its like your oven at home just because it says 350 in ten minutes, there are cold spots. I usually warm my roaster up for an hour and still the first roast is about 1 minute 30s longer than the batches thereafter. Most controllers are not perfectly calibrated to the RTD/TC and drum. I am guessing mine is about 3 degrees off from what it really says.

 

[sae]

My first few batches of the day are done on roasts that are either smaller than full batches or on coffees that aren't so susceptible to roast profiling (cheaper beans roasted darker).

A little off topic: I have a question about the L12 - can you roast and cool at the same time? Also how much do they cost? (I can't get any answers from Probat Burns)