Well I feel quite intimidated to post my paltry attempts at learning about pressure profiling. First off,it's pretty much in my face that I'm a rank amateur at a lot of this, and I'm posting to a pro-oriented site. Second, Ken Fox and Jim Schulman published a very nice piece of work on the reduction of coffee staling by freezing. The competence of their work is something else. If you're interested, check it out on home-barista.com. It really is well done. Anyway, here goes.
I had time this weekend to devote to coffee since Casey and Anneke are off visiting relatives. So two group of people came out to play with pressure profiling. On Saturday, Alan Munter, Sarah Munter, and Nicholas Cho showed up for a lunch of smoked salmon and asparagus, with coffee for dessert. Also at the house was my friend Dave Arnoff, who had just received a Brewtus as a gift, and was diving into espresso " once we fixed his machine. That's another story.
Saturday's testing was not blind, but involved everyone standing in part of my basement, in relatively close proximity to the espresso equipment. Fortunately everyone seemed acceptably clean and well bathed. Nick brought coffee with which he is very familiar " Counterculture Toscano. Nick led the way, pulling shots in which the extractions were divided into thirds by time, with the collected volume in each third contained in a separate shot glass. It was pretty interesting to taste what was coming out of the spouts. The thickest mouthfeel was in the beginning third, and also the sweetest taste. The last third was watery and bitter by comparison. It made sense to try to limit the amount of liquid extracted in the last third in comparison to the amounts extracted in the first and second thirds. I adjusted the pressure profile to accomplish this. The pressure profile was adjusted so that the maximum pressure was 140 psi at the pump, which corresponds to about 135 at the cake, under WBC flow conditions. At extraction's end, the pressure was 60 psi, just enough to keep flow going thru the cake. Nick was of the opinion that the pressure was too high, so I adjusted the profile downward in pressure, eventually settling on a value of 110 psi max. That's 7 2/3 bar under WBC flow conditions, but over 8 in no-flow equivalent pressure (what a dumbass unit, huh?). This made the shots thicker, but smaller in volume, well less than an ounce. This morning, I made a Nick-style shot and weighed it at 18g of syrup extracted from an 18 g cake. I have to say that Nick's shots ended up being very sweet, and I became a bit of a convert, until I tried to replicate them today. I haven't said much up til now about profiling vs. constant pressure. But we tried both, with Nick leaning toward profiling and thinking that there was enough to it that maybe I oughtta think about bringing the pump system to Portafilter 2007 in just over 2 weeks.
Today a different cast of malcontents showed up, including Steve Jones, the famous Eric S., and Kurt Heinrich. All are schooled in the art (just in case I need to invoke the 'obvious to one schooled in the artâ€? schtick later). The idea was that if Nick's pressure profile brought out the sweetness in Counterculture's Toscano, I should be able to brew shots of Toscano using profiling and not using profiling, nice volunteer tasters should be able to discern differences and the differences should demonstrate a preference for one pressure method over the other. Or not. During the tests one person acted as a runner between me and the folks out on the deck basking in the late winter sun (actually very pleasant). In this way the tasters wouldn't know whether or not pressure profiling was being used, and they could make disparaging comments out of earshot. The runner rotated after every few shots, so only two of the three got to taste any one shot. 11 shots were brewed. Shots 1 and 2 were not profiled, with both tasters preferring shot 2 to shot 1. Shot 3 was profiled, with both tasters preferring shot 3 over 2. Taster 1 called shot 3 slightly sweeter than 2 with sweetness lingering longer. Taster 2 wrote 'very sweet on the tongue immediately, excellent mouthfeel. Shot 3 was his favorite of all shots tasted. Taster 1's notes on shot 4 (also profiled) seem to prefer shot 4 for a combination of bright sweetness and caramel. Taster 2 found it bright initially, but better tasting in a longer sip. My notes for shot 4 indicate that I made a grinder adjustment in the coarser direction since shot 3 was pretty short in volume. Taster 3 replaced taster 2 for shots 5-8, and taster 1 for shots 9-11. Shot 5 was profiled. Taster 3 reported 'nice mouthfeel " deliciousâ€?. Taster 1 said 'slightly acidic " minimal sweetnessâ€? - Hard to know if taster 3 was calibrating his taste buds while taster 1 was getting tired. Shot 6 was brewed at constant pressure (no profile). Taster 1 noted 'hint of bitterness on 1st sip. Slight bitterness on 2nd sip, overall slightly muddyâ€?. No preference was given between shot 6 or 5. Taster 3 clearly preferred shot 5 to 6. Shot 7 was not profiled. Taster 1 liked shot 7 as very clean, bright, hint of chocolate and very sweet. Taster 3 also liked this shot, comparing it favorably with shot 5, his first. He added that there was a touch of bitterness in the last part of the shot. Shot 8 was not profiled, and I ran out of Toscano, substituting some coffee that I had roasted a week ago. Both indicated preference for previous shots (there ya go about my roasting, huh?), with Taster 1 writing 'very thick mouthfeel, but most unpleasant shot so far. Muddy flavor combo, nothing stood out.â€? Taster 3 opined 'no 'noseâ€?. Ok mouthfeel " same as 6.
So far, shot 3 (profiled) stood out as particularly good. Taster 1 seemed to be able to discern the switch back to un-profiled in shot 6, with preference for shot 5. Taster 3 also preferred profiled shot 5 to unprofiled shot 6. Both tasters picked up that shot 7 was better than 6 even though both were unprofiled. My notes for 7 indicate that the height of my tamper in the basket indicated that I updosed it compared to my norm, and the extraction time was long at 32 seconds, compared to shot 5 at 26 secs and shot 6 at 24 seconds. Here updosing and resulting long extraction time seemed to trump everything else. Both tasters knew something was up on shot 8. Of course what was up was that I had changed coffee.
Taster 2 replaced taster 1 at this point. Shot 9 was profiled, and shots 10 and 11 were not. Taster 2 preferred shots 10 and 11 over shot 9, noting that shot 9 was much like 4, his least favorite, and that shot 10 was pleasantly bright with some sweetness and 11 was the mellowest of 9 -11. Both 10 and 11 had good mouthfeel. Taster 3 clearly preferred shots 10 and 11 over 9, with 10 and 11 both 'possessing earthy taste, then sweet.â€?
I possibly obfuscated the results for shots 9 " 11 by trying to do a better job of grinder control. I brought my Kony home from work, with the idea that I would set the Robur for pressure profiling, set the Kony for non-profiling, then halfway through the tests, switch grinders so that the Kony was grinding for profiling etc. In practice there was just too much stuff going on. First, only one grinder (the Robur) was filled with Toscano, so no Kony action could happen early in the tests. The opportunity for using both grinders presented itself once both were loaded with the same coffee (aprés switch). Unfortunately, by now the tests had progressed fairly far, and I just introduced something new into the mix.
By now everyone's taste buds were pretty blown out. And the results were somewhat inconclusive in one sense, but conclusively showed that I am pretty inexperienced at this. I learned that there is a really limited number of shots that can be tasted before it just gets hard to taste. That means ya gotta keep it simple. I can't tell if shots 10 and 11 were preferred over 9 by virtue of grinder choice, or by not pressure profiling. By looking at folks' preferences it appears that a difference could be discerned, but then there was that shot 7, the updosed-non-profiled one that got good marks. That means that the level of benefit is of the same order as the noise between shots made by an amateur barista using good equipment and fresh coffee. That is to say that it's a real bitch trying to be consistent enough to discern the gain or lack of it.
Afterward, we celebrated our adventure with more coffee (not Canadian Club you lush). The reason we did this was because we sat around discussing the shot volumes that I had produced. For these tests we used the pressure profile that Nick seemed to like. In my opinion, Nick's profile automatically limited the amount of coffee volume because the pressure values were generally so low. I think everyone thought the shots were very small in volume compared to the amount of coffee used, so I reloaded the profile I had been using before Nick's arrival. This profile ramped to 140 psi, rather than 110, so it represented a substantial difference. With this profile, shots were produced with more volume by at least a factor of 2, with viscosity well-controlled at the end of the extraction. Visually, the shots were of satisfactory volume compared to what the tasters expected of an espresso made with 18 g of coffee " that is to say a double. With crema, the volume was at least a factor of 2 greater than produced by the Nick profile. The tasters liked them for their balanced taste and good mouthfeel, and so did I. But that's about the gist of it. We couldn't do any more testing if we wanted to.
My opinion so far: First, I think the idea of controlling volumetric flow rate during the extraction by varying pressure has merit because the extraction fractions that I tasted in shots that were parsed out into thirds tasted best in the first two thirds, and worse in the last third. Thanks Nick for demonstrating this to me on Saturday. Doing the evaluation is devilishly complicated. Eric rightfully points out that isolating a single variable is impossible when investigating pressure profiling. For example, not-profiling requires a coarser grind in order to keep the shot volume the same, so that means particle size is now different and we're comparing pressure profiling with fine particle size to non-profiling with coarser particle size. Which cart is driving which horse and by how much? My hat's off to people (Jim and Ken) who can pull off days of shot testing. It's hard as hell to be consistent. That being said, I'd like to do the tasting experiment again. I learned that one really has to keep it simple because it's pretty difficult to do the tasting. Thanks to Nick, Alan, Sarah, Steve, Eric, and Kurt for their help!
More when I get something worth spouting off about.