Roasting your own coffee beans is rewarding, frustrating and an art worth pursuing. With about 4 years under my belt using a black, Ambex YM-2 roaster (5lb capacity) in my garage I have weathered many trials and trust I've got much to learn. That being said here's a scoop of material to digest as you either embark or continue on your own coffee bean roasting journey.
My situation - Roaster in my garage. Home is Tampa, Florida. So far I do not use computers (maybe one day :-). I roast mostly 2lb and 3lb batches. I would be categorized by the industry as a home roaster. I roaster about 5-8 batches a week on average. I mostly roast Central Americans, Brazilians and occasionally coffees from the other usual places--Africa, Indonesia, Hawaii, Puerto Rico, etc. I roast preblended espresso about once a month. For the purposes of this article, assume I'm referencing roasting Colombian beans unless stated otherwise.
The environment - Where are you roasting? Indoors, outdoors, up North, down South? Is it windy?
The time - When are you roasting? During the winter, during the summer, in a hot drum, in a drum barely warmed up?
Beans - Are your beans huge? small? peaberry? wet-processed? dry-processed? old?
The roaster - Are the brass jets clean? Is the fan and its many blades clean? Is your propane tank nearly empty? How long is your exhaust hose? Are old beans from the chute mixing in with later batches?
Basic technique - This is important for avoiding basic mistakes that can ruin a batch before it's barely underway. Be sure there aren't any old beans stuck above the drum thermometer spike in the chute. Be sure the bean trier is empty and the collection area facing down. Be sure the cooling fan switch is off (i.e. pulled towards you). You have enough gas on hand to finish your batch. If it's after sunset you have a flashlight. You have pen and paper to make notes.
Always start with your left hand on the dump-in lever and you right hand on your time clock/stop watch. Open the chute to dump the beans and start the stop watch with your right hand. Return your right hand to the temperature control buttons. After the drum temperature is below the temperature at which you wish to set the first (or only) "flame cut-off" temperature, rapidly change the temperature setting to that desired temperature. If you employ a "hold temperature," that would be the setting option to which you switch. Be careful not to lower the thermostat so quickly that you go lower than the current drum temperature, turning off the flame burners in the process, for what would amount to about 17 seconds without burners aflame. If this happens it's not a showstopper but you will likely not bottom out at the temperature you desired. After your roast is 10-15 seconds in progress close the dump-in chute with your left hand.
Bottoming out temperature - I usually try to bottom out at the 200-220F range. Meaning, if I dump 3 lbs of Colombian into a drum preheated to 370F, the bean temp will bottom out at about 215F. Being outdoors, this bottoming out temo will vary depending on the outside temperature. This nadir generally occurs at about 1:15.
Batch types - There are basically two types of batches - first batches and all other (i.e. subsequent) batches. Once I preheat the drum to the desired goal temperature for my first batch of the day I will dump the beans in and get started. I don't waste gas trying to get the drum as hot as it will be for the seconds, third, forth, fifth, etc. batches. The key is to know how your roaster will respond to applied heat in terms of temperature rise verses time. Of course all the other variables (ambient temperature, roaster efficiency, winds, etc.) come into play. With 2lb and 3lb batches I rarely have a hold temperature for the first batch. However, subsequent batches usually require killing the flame in the 250-275F range to prevent a "runaway batch" (too rapid a rise in temp over a given time frame).
Killing the flame doesn't require setting the thermostat to a given temperature. You may find it easier to set your thermostat to cut out at a time near or at the final dump temperature and just kill the gas inflow at the hold temperature by shutting down the blub handle proximal to the gas source. Once the flame goes out you reopen the blue handle to allow the flame to come back on. If you ever have the flame go out know that it takes about 17 seconds for it to come back on.
From 1:15 to 5:00 or so -- If you bottom out at 200F you want to get to 300F by about the 5:00 mark. A pace of 1 degree every 2 seconds (initally) to 3 seconds (latter stages) is desired. At about 275-280F you want to facilitate and gradual slide into a 1 degree every 4-5 seconds pace for the 300-350F phase of the roast. (Looking ahead - "First Crack" will soon be addressed. This phase will start at about 380F and end at 410F).
Coffee beans like to be roasted like people like to change temperatures--in a impercebtible and gradual manner. Nothing herky jerky. Having said that, there are times you can radically alter gas flow without subjecting the beans to a like radical shift in pace of roast. This comes through experience and knowing when the beans are moving into and out of exothermic and endothermic phases. More on that later.
Your more likely to roast too fast at the beginning if the 300-350F phase because you're leaving a phase wherein you're applying a lot of heat to beans more than willing to soak up the heat. But once you've hit 300F the beans can easily get to 320F with a lot less heat applied. 320F-340F is a point in the roast wherein you can stabilize heat application and get a good 1 degree per 4-5 seconds ramp in your roast profile. This 1 degree per 4-5 seconds pace works well without any radical changes in heal application up to about 5 degrees before FCS (first crack start). At this point the beans become exothermic and require less heat to maintain the pace od the roast. So whatever amount of heat application was required from about 350-375F will be about 25% more than needed to achieve this same pace from 375F to 385F (with FCS being at 380F). And now, once at 385-390F the beans suddenly require "a ton of heat" to maintain the 1 degree per 4-5 second pace. It's critical to anticipate when you can radically ramp up the heat here and not overpace the beans yet still not fall into an unacceptably slow pace once in the 397-404F range. Once the beans get to about 405-408F the beans enter another exothermic phase, requiring less heat, if any at all, to coast at a 1 degree every 3-5 seconds pace.
405F to 420F - Depending on how well I've controlled the pace of the roast I may or may not kill the flame at about 407F if I sense the pace is too fast (i.e. > 1 degree per 3-5 seconds). If I do kill the flame I reset the thermostat for the flame to kick on at a time to maintain the desired pace. Bear in mind that once the thermostat is adjusted to a position initiating the flame on seuence about 17 seconds will elapse before the falme actually kicks in. Much of roasting is anticipation and making various adjustments at distinct moments in advance of desired results. The goal is always the same-- Roast coffee beans at a desired pace over a desired period of time. Assuming you're using a quality lot of green coffee, it's your knowledge of your YM-2's nuances, knowing the entry and exit points fro the endothermic and exothermic phases of coffee beans, accommodating the impact of external factors, and making good in-roast decisions that largely affect the quality of your roasts.
Outliers
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endothermic
2lb batches and 290-340F
Sunday, September 28, 2008
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