On this thread, Jim raised the issue of temperature profiling:
another_jim wrote:However, I'm very surprised that DE1 owners haven't experimented with severely falling temperature profiles, say down to 70C by the end of the shot. If there is gold in temperature profiling, that's the first place I'd look..
Of course, no one can say no to jim, so I said I'd do it and am now starting this as a separate thread so as not to pollute that thread. Jim elaborated on the other thread:
another_jim wrote:I'd be thrilled if you (and anyone else interested) could do comparisons of temperature profiles on the DE1.
There was a lot of discussion in the past, when the Scace first came out, about different kinds of temperature curve. E.g. Is a straight line 92.5 the same as starting at 95 and dropping to 90 by the end of the shot? This was before we were thinking about extraction, and before we learned about the sweet properties of lever machines and their pressure profiles. Based on all this new stuff, I was just thinking by analogy --- if dropping pressure is good; why not dropping temperature too?
I have set up an advanced flow profile to examine this. It is a modification of Rao's blooming espresso flow profile. Basically, it works like this: the first stage is 98C preinfusion at 4ml/s until the puck is saturated. The second stage has a flow rate of zero; it's the soak/"bloom" phase. Here the temp needs to be dropped to try to stop the group heater from bumping the temp up too much. The third stage is a ramp up to 1.7ml/s flow rate. The next couple of stages all maintain 1.7ml/s flow rate for chunks of a few seconds. These are multiple stages that are the same in terms of flow rate outcomes so that we can program successive temperature drops over these. The final thing has a flow rate of zero; its purpose is to tell the machine to idle with the group heater in the temperature from stage 1. Here's a photo:
So the first thing that I wanted to see was how extreme a temperature drop I could get at ordinary flow rates. I'm currently doing a tremendous amount of work to re-learn how to use my Quest roaster, so fortunately I have no shortage of garbage coffee that I can throw at stupid things like this. The first order of business is to get an idea of how big a temp drop can we get across a shot with a sensible flow rate. I asked the machine to give me 98C at the preinfusion stage. It won't let you set less than 80C as a target temperature at the moment (maybe this is the sort of thing John and Ray could give us more range on via firmware update in future, were there demand for it), so I set 80C as the target temp for the remainder of the stages (except the final reset stage).
Here is a temperature curve:
The solid red line shows the temperature profile and the vertical black lines show the end of each stage. So what we can see is that, even with the temp target set to the minimum in stages 2, 3 and 4, the measured temp hangs around near the 98C preinfusion temp for these first stages of the shot. I think that this is the reading at the temp sensor that sits immediately behind the showerscreen and is surrounded by the lower part of the brass dispersion block. As for roaster temp probes, some caution may be necessary in interpreting these results, since I don't know how they map on to what one would measure with a scace device. If someone wants to lend me one (I'm in Melbourne, Australia), I'm happy to look into that. It may be that the temperature that the puck experiences is lower; who knows if the thermal influence of the dispersion block and the cartridge heater drags the temperature up a bit locally at that probe.
With that absolute measured value caveat out of the way, at the end of stage 4, maybe 10mL had flowed out. This will vary depending on the coffee and the grind setting. With a finer grind, less seeps out during the bloom phase. With lighter roasts, more seeps out during the bloom phase. What we can see is that the rest of the shot experienced a temperature drop from about 98C to about 90C. So from phase 1 of this investigation, we can surmise that that is about the biggest repeatable temp drop I can get from the machine ... at that probe location ... using this profile.
The dotted red lines shot the temperature targets. The pale, solid red line in the background shows what I was using for my last shot.
So I'll leave that there as the background homework and try to fit in some actual comparisons this weekend. Of course, we need to remember that there are a lot of different variables, so there are many ways this could go from here.
For what it's worth, I'm currently drinking an americano made with a filter roast kenyan coffee extracted on the above profile. It's delicious; sweet, no grassyness, lots of tomato type aroma/flavour (others say that this is indicative of an underdeveloped roast; in the absence of grassiness, bitterness, astringency, etc, I don't really mind it). I haven't got much experience with this particular coffee, so I have no idea if this result is because the temp profile is good, bad or otherwise.
EDIT: Image showed wrong pressure profile, so I replaced it.