Long roast times - vintage L5 Probat

[Sweden]

Hi,I'm new to roasting and have just bought a vintage Probat L5. I have a problem with too long roast times and kind of burned taste and to low flavor of fruit. The answer could be simple: "well, drop your coffee earlier and it won't be burned..." Now we come to the tricky part. To reach about 195* celcius (about 383*f) it takes about 20 minutes. The very start of second crack is at this temperature. If I drop the coffee at first crack it's very uneven in color (one bean darker then the other). I have tried both 4 kg and 2,5 kg batch with almost he same result.To get the beans to higher temp faster I keep full gas at all times exept during first crack. Now to the 1000 questions:What are your recommendations? Shall I decrease gas to "half" and "keep the air temperature" instead of trying to increase it at all times? Would this get rid of burned flavour?What air temp should I try to keep?Could the beanprobe be wrong?Something wrong whith roaster?well.... I could keep going whith more questions but lets start with this and see if anyone has the energy to help me Thank in advanceMattias

 

[ACRM]

Hi Sweden,
Welcome to the "black magic" of coffee roasting! Just a few general thoughts...
You have a large number of variables in the roasting equation - gas pressure, flame level, venting, drum load, bean type, ambient air temperature, etc. To begin gaining control try and be a little scientific. First things first, make sure your gas pressure is up to your roaster's specifications. Then, check your exhaust system to make sure their is no back pressure/it is "drawing" well. Now you can start changing one variable at a time to determine what impact it and it alone has on roast time. Also, don't place too much importance on trying to match other peoples/interweb's profile temperatures. We have found wild variations between different machines' reported temperatures (bean, exhaust and environmental) when there aren't any. Your roaster's temperatures are likely to be unique and not directly comparable to other machines. As a good scientist/artist you also MUST keep comprehensive notes on as many time/temp/gas/air flow data points as possible and be religious about marrying them to tasting notes for each batch. Believe me. there is nothing more frustrating than finding your white whale and then losing him because you can't repeat the profile. Hopefully other forum members can chime in with some general guidance on profiles but I am sure it will be general - every roaster installation is unique, just like every bean, every espresso machine, every person's taste.

 

[Sweden]

Thanks

Hi, Thank you for the reply!I have now solved the problem. It was to low gas pressure. The seller told me it should be 30mbar but off course it should be 50....Now I have another problem. The temp probe (bean) shows to low temperature. The temp it self is good! This is only a problem whith the digital probe. It only shows about 104*celcius at first crack and after about 1,5 minutes when I drop coffee out it shows like 107*C. Off course this numbers are wrong and I wonder if the probe can be drilled at the wrong place? This one is at the hatch, to the left of handle of my 5 kg Probat. Would it be better to put it where the sight glass is? RegardsMattias

 

[topher]

Have you checked to see if the probe is clean? The placement should be alright where it is. Check to see if the probe has been bent to face downward...to read the bottom of the drums temp.

 

[Sweden]

Reply to topher

Hi and thanx for helping me!It is clean but it is totally straight. Do you mean I should bend it so its not straight any more - down with tip pointing at the bottom of drum? Won't I get a higher temperature because of it will be close to surface of drum (close to burners)? Or will it only read bean temp anyway? If I bend it down, what is the difference in measuring? It shows about half the temp it should be showing, if air temp (analog) shows 225*celcius this probe shows about 90-110*celcius at the same time (if I don't have any beans in the roaster that is....)