Frost wrote:Being pragmatic, I would put a variac hardwired to the heater element, another variac hardwired to the fan, and a switch on the drum motor. Add temp probes and a reminder timer and don't leave unattended.
That's one method. A friend of mine is working on a more elegant solution using the
Arduino. Many of us already have the temperature probes set up, and the "B" model already has manual control of the heater and fan. The maddening thing about the stock control panel are the "safety features" that require cooling to 163F before restarting the heaters after the roast. That usually adds 8 minutes to the cycle time for repeated roasts. If you are roasting a bunch of samples, it's maddening.
In any case, fresh off a roasting profile course at a roasters retreat, using an Ambex YM-2 with their full automatic profiling tool (with cupping of the different samples following roasting), I can see some clear similarities with what profiles I've been doing on the hottop vs. a small commercial drum.
Main differences are the amount of retained heat in the drum for the larger machine, the primary mode of heat transfer (clearly forced air for the Ambex--hottop has a mix of radiant from the heater and not-quite forced air convection), and the ability of the gas-fired machine to apply greater motive heating force relative to the bean mass). There are certainly more differences than that, but I'd hit those as the top three.
Quick review of my hottop profiles vs. what I learned over the weekend.
1) Good thing--lower retained heat in the hottop generally keeps the turning point (or bottom out point, or equilibrium point--where the bean mass temp starts rising after the initial drop upon charging the beans) at 150F or below (usually well below--gives me the thought to up my preheat).
One of the profile experiments was looking at the difference between a 190°F equilibrium point and one just below 150°F. All the rest of the parameters (profile points) were the same--1st crack temperature and time, end temperature, and total roast time. The 190°F turning point roast produced some nasty acrid tastes in an otherwise beautiful bean. To relate the profile to terms we've used here before--the beans on that one hit 300 BT at about 4 minutes--not enough drying--too much heat blasting in at the start.
2) Worrisome thing--Good results on the Ambex with a relatively rapid ramp (think 25-28°F/min, estimating--don't have the profiles on me now) from 300-1st crack. Faster than I expect the hottop can produce. Profiler was controlling the heat input at this point, so this ramp was achievable without a full heat.
I'll think of some more things as I wind down. Specific to Jim's questions.
Case 1: The coffee everyone raved about, roasted medium as directed, tastes thin and sour. A darker roast of the same coffee also tastes thin, but ashy. You suspect your roaster is not profiling correctly. What would you do? How would you do it?
Case 2 (HB masterclass

): You have an espresso at a cafe, and it's wonderful. You roast and make the same espresso at home, and you can tell it's the same coffee, but it's no longer fabulous. However, you can't quite put your finger on why it's not shining. What's your process for figuring out what went wrong and correcting it?
Case 1--I would look at my profile from first crack to end of roast--did I give the roast sufficient time to develop the body from the onset of first crack? Keep all parameters the same, and modify the profile to increase the time from 1st crack to end of roast (start with 30 sec). Cup both immediately.
Case 2: Get some of the beans from the cafe, if possible. Determine if their roast is pre- or post- roast blended. If it is post-roast blended, accept that they are not going to tell you the component coffees and roast level, and resolve to accept that the best you may do is a pre-roast blend of the green they sell you. Buy their coffee and enjoy it....