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A noob makes a Corretto - advice welcome

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  • A noob makes a Corretto - advice welcome

    Hi guys, its been a long time since I have had anything useful to say but I have continued to lurk. Now that I am no longer working in West End where there were heaps of small roasteries, I have decided to bite the bullet and have a go at roasting my own beans. Geez, the local Zarraffas charged me 58 cents a shot for roasted beans this morning, I might as well use a nespresso!

    Anyway, after a bit of a dig on Gumtree, I picked up a Breville BBM200 breadmaker for $40 after lunch and decided I better replace my ailing $20 heat gun because it seems to cut out from overheating every time I use it. I detoured through Bunnings on the way home and bought a Bosch 630 variable temp HG for $99.

    I fired up the BM when I got home and found I would have to wait about 30 minutes before getting an 18 minute run of the mixer blade. It seemed a bit silly not to preserve the breadmaking capability, so after some exploratory surgery, I went off to Jaycar and bought a $5 DPDT switch and before long, I had it wired in.

    It was pretty simple really. Cut the wires going to the motor, put the wires going to the motor on the switch centre terminals, and the other end of the cut wires at one end of the switch and then ran the mains power to the other end. There as even a nice little terminal block to connect my new motor power circuit to! Nothing has changed with the switch in bread mode but in coffee mode, it stirs continuously.

    I did a bit of reading on here about covers for a Corretto which I found interesting and after a dig in the shed, I found a 12mm piece of aluminium offcut.

    It is a perfect length and there is a 20mm gap to let the hot air and chaff escape. I figure that if I bore a hole in this, the HG will be self supporting. I should also be able to pick up some 1/4" (6.35mm) aluminum tube tomorrow and thought I might also be able to run a probe from my multimeter down through this tube to monitor the temeperature. The wall thickness will be 0.9mm. Next size up is 10mm and I can get it in 1.0,1.2 or 1.6 wall thickness.

    It looks like I still have a bit of work to do but I am off to find some green beans in the morning.

    So there is a plan, here are the questions:

    1. do you think the gap for exhaust is big enough?
    2. Should I put a shroud over the exhaust gap so stuff goes out sideways ? (I have some 1.2m ally sheet here that will do the trick if necessary)
    3. Where should I locate the HG? In the corner or centrally?
    4. How high should the temp probe be off the bottom and do you think the probe from above will work? The tube has 0.9mm side walls so it should be reasonably strong.

    Any help and advice will be much appreciated:

  • #2
    Hi Rodw,

    Looking great so far.
    1. Big enough, I think so. You may have to experiment a bit to ensure it creates some pressurization ensuring good chaff extraction.
    2. Up to you, I would first try it as is to see what it does.
    3. Not sure there is a right/wrong answer. I don't think it matters too much. I have mine centrally as the exhaust is at the opposite end also centrally.
    4. Depends on your roasting batch size, with smaller sizes, having it closer to the bottom is ideal, but if you're doing bigger batches, the readings may be a little off requiring the probe to be higher. I have mine approx 2cm from the bottom and have been roasting 250 - 500 gram batches without issues. Some guys have another hole in the pan to mount the probe higher for bigger batches.

    Hope this helps.


    • #3
      1 and 2: Agreed, gap looks good. Depending on whether you use fan speed 2 or 3 affects how vigorously the chaff flys out. I recommend only using fan speed 2 for 250 to 400g batches, using 3 tends to over dry the beans too quickly, loosing sweetness and varietal flavour, leading to dry, dusty and woody flavours and eventually baking. With hot air roasting the less time spent in the roaster (without exceeding MAX temperature) the better.

      3: Looking at how you will use your lid, which is similar to mine, I would locate the HG so it is pointing into the top right corner.

      4: I have my probe in the bottom right corner, leaving enough of a gap between the tip and the paddle so that beans don't get briefly caught between them. I also have my probe about 2cm from the bottom and generally roast 250 to 300g.

      Prob the most other important thing I can suggest is to do some dry runs, find out what HG setting will give you your maximum environment temperature which should be no more than 260C, I prefer not go over 250 which for my setup is 450 on the HG on fan 2. Insulating with a fire blanket will help improve your temperature stability dramatically.


      • #4
        Just a couple of items to consider:

        The aluminium lid - it will get very hot, and will be difficult to remove and put somewhere when you empty out the beans. I've made a chipboard top and cut holes for the heat gun and exhaust. The chipboard burns a bit where the heat gun is mounted, but the rest of the top is fine from a heat point of view. It means you can touch it and take it off easily. Others have used cement fibre sheeting.

        Also, you need to be aware that the chaff will go down between the basket and the sides of the BM. You'll need to blow that out occasionally to minimse the fire risk.

        You'll find that the beans wear the coating off the internals of the basket, making it not-so-good for breadmaking. I'd just sacrifice it to the god of coffee, and buy a new breadmaker!



        • #5
          I use the same BM, in my experience you need to trim and file smooth about 5mm off the outside edge of the paddle to avoid a dreaded bean jam. Good BM for roasting IMO. I do 650g green per roast and it copes fine. My probe is top mounted to sit about 20mm below the surface of the greens (they expand during roast) away from the heat gun which blows along the long edge of the pan in the flow direction with the nozzle level with the top of the basket. My lid is made from 0.3mm alum sheet and fashioned to stay put during roast and dump, I use flue liner from an old pot belly as insulation around the basket which fills the gap nicely and prevents chaff build up. Good luck.


          • #6

            Thanks for all the advice. I have had a pretty busy day. I don't know why but a lot of my machining jobs seem to involve some sort of coffee project! The biggest drill I had was 22mm and I needed a 34mm hole for the heat gun so it gave me a chance to use my boring head for the first time. It was OK taking a 1mm cut which increased the diameter 2mm at a time so it did not take long to get it to size. Then I had to have a coffee to recover! I went up to Action Aluminium and bought a length of 1/4" tube as well as a 10mm tube. 6M lengths and it cost all of $11.70 for the two tubes!

            Anyway, this is what I came up with by the end of the day:

            Brendon at Bean Green was feeling generous and just scooped the beans out without weighing so I got about 1.1 kg each of three beans (Columbia, Brazil and Kenya) and he threw in a few 250g bags. Shame lives on the opposite side of Brisbane!

            Anyway, 1/4" = 6.35mm, so I drilled a 6.3mm hole for the probe and it was a press (well hammer) fit. I had a dry run with some beans whizzing around and it was positioned too high. I decided I would work with 300g batches as anything more than 250g seems to go stale around here! I had to cut a longer tube to get the probe into the beans. Then I tapped it through a bit further which you can see. I started off with the top of the probe flush with the top of the lid. The thermo wire is held firm at the top with a scrap of electrical wire doubled over and jammed in the tube. I was not impressed as when I picked it all up off the floor to put on the bench, I promptly dropped my multimeter which wrecked the thermocouple. I had to spend half an hour or so fixing it. Very fiddly repair!

            Here is the bottom side

            And a close up of the temp probe.

            I am just using the thermocouple that came with my multimeter. I figured it would get damaged if it protruded so I kept it flush with the tube for protection. It seems pretty sensitive. I think the 1/4" tube will be strong enough but if not, I will go up to a 10mm tube (which has a 6.8mm bore) and feed the 1/4" down it and let it stick out a bit.

            What you can't see is that I drilled and tapped a hole on the edge of the lid and I have an 8mm set screw securing the heat gun. Gonzb, I as going to add a handle to the lid but the HG is now so secure, I can pick the whole thing up using it as a handle. Don't know how it will go when it gets hot. Anyway, I will see how it goes. I will add a handle if it is needed. I am happy to donate my BM to the coffee gods but did not want to wreck it totally just in case I decide to buy a real roaster.

            Noonar, thanks for the tip on trimming the paddle, I might do that.

            Steve, thanks for the feedback on the sensor position. At the moment, it is probably about 10mm off the bottom. I did do a short dry run with the HG set on 180 so I will have a play in the morning.

            Finally, I found a catering supply place I never knew existed and grabbed a 250mm sieve for $18 and am armed with it, a colour calibrated pic of bean colour from Sweet Maria (the CS member card is out of stock), Peter Forsters spreadsheet off the forum here, a wooden spoon and a stop watch so I am almost ready to go! I don't think I will bother making a cooler yet, the fan you can see almost lifts off the ground when you turn it on so I am hoping aiming it in the general direction of the sieve will do the trick!

            I will report back tomorrow night! Wish me luck!


            • #7
              OK, I did a dry run this morning. I forgot to say I had a fire blanket wrapped around the basket. Here is what I came up with:

              HG   Temp
              250  147
              300  180
              350  215
              400  250
              450  283
              I plotted this in a chart and the response is very linear with the output temp being about 60% of the Heat Gun temp. Once it cools down, I will give it a go and see what happens....


              • #8
                Looking pretty bloody good, I often feel jealous when I see these builds from engineer types.

                I also find my HG / output temp readings to be quite linear 54 to 56%.

                A good basic starting point I can suggest. Pre heat to around 170, 300g of beans might get you turning around 70 to 75. Aim to reach the end of drying stage around 6 mins later, beans go yellow and the smells
                changes from sweet wet green grass/ hay to baking bread and rum, from here Ramp up your heat so that your reach first crack 4 to 5 mins later, trying not exceed your max environment temp leading up to first crack. Experiment with development times post FC, 2.5 to 4 mins.


                • #9
                  Nice work Rod
                  A great looking build and sounds like you've got all the gear to make it happen! I've had to bore a lot of my holes with a blunt chisel!
                  Second what Steve said - gentle start, then ramp slowly to FC, then back off to slow the rise between 1C-2C. Lot's of good info on various threads around.

                  FWIW - using a very similar setup to you (with same bosch gun) here is my old 350g manual 'input chart' with gun temp inputs to suit various ambient temps. You would probably need to adjust as required - I'm roasting high altitude / low humidity - tends to require more heat overall than those at sea level:
                  Anyway - might help - might not.

                  Certainly look forward to hearing about your results!

                  Cheers Matt

                  DBC Roasting Profile Sheet Jun13.pdf


                  • #10
                    Matt, Steve, thanks for the ideas. I decided not to preheat so I had a bit more practice at following a profile. Matt.Seeing you had such a nice profile sheet, I decided to follow your ideal roast and copied the numbers to Excel. Here is what happened.

                    I was a minute or so behind all the way (somebody told me to start slow!) and I stalled it after FC (at 17 min) when I turned it back a bit too much but other than that, it all went smoothly. I don't think I will bother with making a bean cooler. I pointed my fan straight up in the air on high to cool the beans and it started to blow them out of the sieve!

                    I got 244 grams out of my original 300 which is an 81% yield. I am happy with the colour, wait until tomorrow to taste I guess.

                    Anyway, let me know your thoughts.

                    PS. Steve, don't worry too much about this engineer! He fakes a lot! .... and asks a lot of questions.... just lucky that I have had a source of income on the side and have dedicated the profits to my workshop (and other toys)...



                    • #11
                      That's great Rod!
                      That looks like a pretty jolly good first roast - let us know how it tastes.
                      I found that that basic profile/technique works pretty well for most beans. If it is slightly faster, you'll get a lighter/brighter taste, slightly slower you'll get more earthy cocoas. You may need to adjust for some beans too - i.e. centrals like a slower roast - some ethiopians respond better to a slightly faster one. But keep tasting, write notes - enjoy the ride!
                      You'll get the hang of it



                      • #12
                        As Matt commented Rod, good looking first roast.

                        Your setup is very similar to mine, just posted some of my thoughts in another thread which may be of interest

                        FWIW 17 mins to FC seems slow to me, I look for FC at about 13 or 14 mins 200° and usually stop the roast at about 19 mins at approx 225°


                        • #13
                          Originally posted by DesigningByCoffee View Post
                          That's great Rod!
                          That looks like a pretty jolly good first roast - let us know how it tastes.
                          I found that that basic profile/technique works pretty well for most beans. If it is slightly faster, you'll get a lighter/brighter taste, slightly slower you'll get more earthy cocoas. You may need to adjust for some beans too - i.e. centrals like a slower roast - some ethiopians respond better to a slightly faster one. But keep tasting, write notes - enjoy the ride!
                          You'll get the hang of it


                          Matt, thanks for the encouragement. I could not help myself and just poured a shot. It had heaps of crema and was quite drinkable, so that is encouraging, and I don't usually drink black coffee, normally a flat white.

                          Originally posted by Yelta View Post
                          As Matt commented Rod, good looking first roast.

                          Your setup is very similar to mine, just posted some of my thoughts in another thread which may be of interest

                          FWIW 17 mins to FC seems slow to me, I look for FC at about 13 or 14 mins 200° and usually stop the roast at about 19 mins at approx 225°

                          Yelta, thanks, I have been following that other thread with interest. You sound like my kinda guy. Simple is always good! I don't get too stressed about my coffee making at home because I know the worst cup I make is one hell of a lot better than a lot I have paid good money for.

                          Yes, the roast was far too slow, FC was about 2 minutes behind where it should have been in the target and then I turned it down too much so it stalled and took a while to get back on track so it dragged out to SC again. I was fully expecting to have to trash the first batch, but I think it will be usable. Now at least I have a base to work on so it can only get better.

                          I am only going to be roasting once a week or two, so progress will be slower from here on.


                          • #14
                            Well I sat down this morning and dialed in my grinder (which is now back where it was when I was buying roasted beans from micro roasteries) and contemplated the start of my roasting career. What an outstanding coffee I had!

                            Spurred on by my experience, I just HAD to make another batch. This time using some beans from Kenya. This time I got lot closer to Matt's profile and finished pretty much spot on. I just need to back the heat off a bit more on startup.

                            Note that the profile starts at an ambient of 15 degrees and it was 27 degrees when I started which is about the temp Matt was shooting for after 1 minute so the scale is pushed out by that much to line up with the curve.

                            Decided to go to an open day tomorrow afternoon where I bought the beans from. Um, do you think I have got the Corretto home roasting bug now?


                            • #15
                              Well Rod
                              If you're having an outstanding coffee first roast - I'd call that a success!
                              This profile is looking really good. It's still probably longer than many would suggest - but I personally find that the slightly longer roast means you can drink it sooner
                              So crack in - and keep posting your thoughts and questions about the tastes you are getting - far more useful often than grabs of the profile when it comes to trouble shooting or fine tuning your roasts. A little sharp? A little dull? A little weak? Bitter?

                              Certainly lots of practice on lots of beans is a heap of fun. And they're all so different! But one thing that can speed up the learning process is doing a couple of batches of the same bean back to back with different roast times/lengths - that way you can compare the different results. But I'll admit freely that I'm pretty bad at this myself - I get bored of one bean and keep changing! That's why it's taken me so long to improve my results

                              Happy roasting!