Coffee Roasting Using Gene Café (GC) - Tips and Techniques By Ronald Bito-on Copyright 2008 Avacuppa Pty Ltd Softcopy Version A softcopy version of this article (in PDF format) is available for download in http://www.avacuppa.com.au/mediawiki/images/4/40/coffee_roasting_using_gene_ Caf%C3%A9_-_Tips_and_Techniques.pdf. Disclaimer The usual disclaimer applies. You are responsible for your own action. Having said that, be careful when handling hot objects. Pre-requisite Reading Please read the Gene Café Owner s Manual because information from that manual are not repeated here. Introduction This article is simply my compilation of knowledge gained from my own experiences in using GC and from other various sources (books, internet, etc.). The ideas and suggestions presented in here is not offered as authoritative but rather as a starting point and is always open for discussions and/or improvements. Your individual tastes and preferences should be deciding factor on which methodology you adopt. This article is intended for the general public. Thus, no prior knowledge of coffee roasting is assumed. Temperature Readings Throughout this article, all references to temperatures readings are external bean temperature. Temperatures quoted in this article are not exact. For example, quoting FC temperature to be 205C simply means that in most coffee roasters and type of beans the FC will happen around this temperature reading. Factors for variances in readings are: the placement of the temperature sensor and the type of beans being roasted. Thus, some people may say that with their roaster (GC or any other roaster) the FC occurs at 198C, which simply means that it is very likely that their SC will happen at 222C (a difference of 7C to the 229C quoted here).
List of temperature readings relevant to coffee roasting: Inlet s Environmental Temperature the temperature of the hot air just before it enters the roasting chamber. GC has a temperature probe here. External Bean Temperature this is temperature reading displayed by most high-end commercial machine and is the temperature usually quoted in roasting articles (including this one). The temperature sensor is immersed in the roasting bean mass. Internal Bean Temperature I am not aware of any roaster that displays this temperature. This is the temperature inside the beans. Sometimes scientific studies on coffees explicitly quote this temperature. The internal and external bean temperatures are two distinct readings. Roasting Chamber s Environmental Temperature the temperature inside the roasting chamber just above the roasting bean mass. Outlet s Environmental Temperature The temperature of the hot air just as it leaves the roasting chamber. GC also has a temperature probe here. GC have two temperature probes as highlighted above, I am not sure which one is being displayed or if they are averaged in any way. At any rate, I do not personally rely on them. I rely more on the timings of FC and SC, the intensity of smoke, the emerging of oil on the bean surface and bean color (in that order of importance). Another indicator that could be used (but I have not added to my list of tools yet) is the smell of the smoke coming out of the chaff collector. Heat Used in Coffee Roasting Heats used in coffee roasting are in the following form: Conductive heat is transferred to the beans by direct contact to hot materials Convective heat is transferred to the beans by hot air Radiated heat is transferred to the beans by the radiation emitted by hot objects. Coffee Roasting Stages In the coffee roasting process the DGB goes through the following stages: Stage Temperature range Comments Drying 0-179C High moisture content at this stage is best utilized by using conductive heat. The materials used for the roasting chamber of GC is in my opinion not good in delivering conductive heat (cast iron is), as a result I omit the pre-heating step. Beans will have a yellow color at the end of this stage.
Tanning 189-204C Browning of the beans is due to the caramelisation of sugar and Maillard Reaction. From this stage and onwards, convective heat is more efficient way of transferring heat into the beans. Flavor Development 205-229C First Crack (FC) starts at around 205C and ends about 2 minutes later. Second Crack (SC) starts at around 229C A roast level of Full City (unfortunately, the initial is also FC) is just before or at the very start of SC. The appearance of a lot of smoke signals that the beans is about to go into SC. Carbonising 230C+ The beans start to turn into carbon and this process is accelerating because some of the chemical reactions within the beans are exothermic. It is not uncommon to have a bean temperature that is higher than the environmental temperature. Progressing from a FC to FC+ roast level can happen in 20 seconds depending on the beans thermal momentum (which is partly determined by how much heat was absorbed by the beans). Roasting Let s get cracking! 1. Remove the roasting chamber, load the green beans then put back the chamber into the GC. Note that the maximum load for GC is 300g, but it only applies for less chaffy beans (wet processed). For chaffy beans (dry processed), I would not go beyond 225g. Also, I believe a lower load (minimum of 50g) would result in a better airflow during roasting which is much needed during the roasting process (especially from Tanning stage onwards). 2. Turn the Time knob to 30.0 minutes. Set the Temp to 150C. 3. Press the Start button then start a separate timer. I use a timer because it starts from 0:00 and counts up, whereas GC timer counts down. 4. At 6 minutes (the timer reads 6:00), turn the Temp knob up to 250C.
The Temp setting of 250C is for beans grown higher than 1,500 meters (Kenya AA and Guatemala SHB). A lower Temp setting should be used for beans grown lower than 1,500 meters. 5. At 11 minutes (the timer reads 11:00), turn the Temp knob down to 240C. The reason for this adjustment is that at this stage we must have injected as much thermal energy into the beans as possible without causing scorching and/or tipping. Also, too much heat at this point onwards, will make the Flavor Development stage go too fast (ideally it should take 3 to 4 minutes between FC and SC). Time adjustment: In most of my roasts the FC starts at between 12 and 13 minutes, if your FC starts later at say 14, try delaying the turning down of Temp to 240C at 13 minutes (a minute before FC). Temp adjustment: Lower the temperature down if the following occurs: The roasted beans have signs of tippings and/or scorching. The time between FC and SC is too fast (note that you may address this issue also by lowering the temperature in step 6). Increase the temperature up if the following occurs: The roasting takes too long (say more than 20 minutes) and you want to hasten it up. The time between FC and SC is too slow (note that you may address this issue also by increasing the temperature in step 6). 6. Note the timer reading at the first sound of FC (say 12:00), when the sound of the FC dies down or 2 minutes from the start of FC (14:00 as per our example), adjust the Temp knob depending on your target roast level as shown in the table below. Note that the GC is an electrical device and its heater elements heat output can only have 2 states, on or off. Because of this it is advisable in this step to observe the following to avoid stalling the roast: Let the FC finish before you turn the temperature down. Do not turn the temperature down by more than 10C. I personally restrict my adjustments to 5C, which means I also lower the temperature in step 5 if I think I need to make a big adjustment. Roast level Action C Go to step 7 for the Cooling steps. C+ Adjust the Temp knob to 230C FC Adjust the Temp knob to 235C FC+ Adjust the Temp knob to 240C Vienna Adjust the Temp knob to 245C
You may lower the temperature if you want to slow down the progression to your target roast level. Conversely, you may increase the temperature to speed things up. 7. When to hit the Stop button to start the cooling process. This step is where you must have all your senses on the alert, when to hit the Stop button depends on your target roast level as follows: Roast level When to hit the Stop button C+ When the color is a more uniform dark-brown, the bean surface is smoother compared to C (which is a little wrinkly) No sign of oil FC A hint of black starts to show A noticeable increase of smoke signals that the SC is about to begin (usually in less than a minute) The beans a becoming shiny but no surface oil This roast level is usually just before the SC begins, thus, when you hear a few snaps of SC, you are still in FC but fast going into FC+ territory. FC+ SC must be in progress (usually 30 seconds from start of SC) Oil now start to emerged on the surface Vienna One minute after SC and beyond At this stage the bean is more black in color than brown The beans are uniformly covered in oil. The smoke you see are very likely the coffee aroma and flavor that should be much better in your cup rather than lost in the air. Fire could start if you are not vigilant at this stage. I rarely go into this roast level, and only by mistake. 8. Cooling aka End-Of-Roast (EOR). There are 3 options on how to perform cooling. The option to choose is a personal choice, you may let you taste buds do the choosing or you may factor in convenience as well. The 3 options are: a) As fast as possible this is the option I use (and by most home-roasters I know). The roasting process (chemical and physical) is stopped almost immediately. i. Press the Stop button until the GC displays the E (to signify the GC is in emergency stop mode).
ii. Wait for the roasting chamber to stop rotating, then remove the HOT chamber (don t forget to use an oven mitt) and dump the beans in a colander. It is a good idea to use a fan to cool the beans in the colander (with perforation for aeration) even faster. iii. Immediately after emptying the chamber, return it to the GC s body and initiate the normal cooling cycle to 60C. b) The normal GC cooling cycle GC will cool the beans (and the machine itself) to 60C. i. Press the Stop button and release immediately. ii. The GC will beep when the cooling is done (may take up to 10 minutes), then you may empty the chamber. c) Cool to 150C in 3 to 4 minutes this option is a combination of the other 2 options. i. Press the Stop button and release immediately. ii. Wait for either 3 minutes or when the temperature reading had dropped to 150C then initiate the Emergency Cooling cycle as in option a) above. Post-Roast Activities 1. Weight the roasted beans to calculate the percent loss. Percent loss = (weight before roasting weight after roasting) divided by weight before roasting then multiply by 100. A rough guide for relationship of roast level to percent weigh loss is shown in the table below. Roast level Percent Weight Loss C 16% C+ 17% FC 18% FC+ 19% Vienna 20% 2. Create a roasting log for this particular roast session and update it later with how the coffee tasted when brewed. 3. Make some notes in your roasting log any adjustment in you roasting Temp and/or Time settings when roasting the same bean again. Glossary Term Definition
Caramelisation The oxidation of sugar due to pyrolysis. C City C+ City plus DGB Dry Green Beans. The raw coffee beans. EOR End-Of-Roast. The process of trying to stop the roasting process (chemical and physical) by stopping the application of heat and starting the cooling of the beans. FC First Crack (in the context of events during the coffee roasting process. Full City (in the context of roast levels). FC+ Maillard Reaction Percent weight loss SC Vienna Full City plus A chemical reaction between an amino acid and a reducing sugar. This is calculated as (weight before roasting minus weight after roasting) divided by (weight before roasting) then multiply by 100. Second Crack. The roast level after FC+. Online Store www.avacuppa.com.au