This is where Dan starts calling me crazy. It's going to be like the "haunted portafilter" episode all over again.
I don't know if this has been implied by people in the past or just inferred by everyone, but the assumed idea about brew temp for espresso has been that there is a single "sweet spot" and that distribution outside of that sweet spot forms a bell curve. In other words, quality falls away from that sweet spot gradually at first and then rapidly as one gets further from the target.
When I started testing out the results of incremental changes in temp I noticed something that made me think that this might be wrong. Given that it was going to be a controversial statement, I double, triple and quadruple checked my results.
So I just finished yet another run through the various temps.
I've done this with two different coffees (thank you Stumptown - thank you Artigiano; I can't imagine what I would do if I had to pay for all this coffee).
The results are illuminating and somewhat shocking to me.
While there is a bell curve distribution at a gross level, at the center of the bell curve and at a granular level the model fails.
What do I mean?
If you're looking at the results of changes of brew temp at a 3F level of granularity, there is a clear bell curve. Even at a 1F there is a bell curve of quality. But at a tighter resolution, I start to find multiple sweet spots - each with their own distinct flavour profile.
Here is an illustration.
Using the Stumptown
Hairbender, I found that shot quality fell off dramatically once one hit 196.7F on the low end and 199.4 on the high end. So let's look at that "center of the bell curve". I incremented the machine by 0.3F steps. For each one, I scored shots on Body, Clarity, Sweetness, Mouthfeel, Balance, Flavour, Finish and Aroma. I threw away the lows (barista error) and averaged the remaining scores for each category. I then totalled those scores to get a final result for each temp.
(Maximize your window to see columns aligned)
full results here
Temp Body Clarity Sweetness Mouthfeel Balance Flavour Finish Aroma Score Descriptors
197.0 5 8 7 4 4 6 6 9 49 Citric, thin, sweet, floral, nice aromatics
197.3 7 8 8 7 7 8 8 8 61 Syrupy, very sweet, light citrus, nice fruit.
197.6 8 8 9 8 6 6 6 7 58 Sweeter, chocolate, a bit "rough" on the finish
197.9 9 7 8 9 9 8 8 6 64 Very polished and complete. Chocolate tones. A bit flat.
198.2 5 8 7 7 6 6 6 7 52 Up front fruit, low body, faded chocolate finish
198.5 7 8 8 8 7 7 5 7 57 Tons of fruit, very sweet, chocolate gone, tobacco finish
198.8 5 7 5 6 5 5 5 6 44 Thin, sharp with noticable bitter flavours. Simplistic.
199.1 7 8 5 8 6 7 8 7 56 Big, bold, "rustic". A bit simplistic.
Tobacco/leather, round, intense, no fruit.
199.4 3 7 3 4 4 3 3 5 32 Harsh, acrid, "burnt oil" finish.
You will notice that there are a couple of distinct sweet spots with the central target zone of the bell curve - each with their own distinct flavour profile. Depending on your personal taste, one of these will most likely be your own favorite - but that doesn't mean there is only one sweet spot or that the bell curve holds at this level of granularity.
For example - I found shots pulled at 197.3F to be lovely with great sweetness and fruit and a lovely finish. These are lighter shots, less concentrated and "intense" in flavour. If you're looking for an intense and powerful shot, 199.1F yields bold and powerful flavours. If you're looking for balance and polish, then 197.9F is probably going to suit you best.
This has implications when it comes to drinks consumed as well. Shots pulled at 197.3F are less suitable for use in milk drinks I find. Shots pulled at 197.9F are wonderful in cappuccinos whereas shots at 199.1F are great in lattes.
Perhaps of even more interest to me is the "bad spots" on the temp curve.
There are noticeable issues with certain temps - even though they might fall between the desirable temps.
This was what drove me to test and re-test and to duplicate the results with other coffees.
At first I figured it had to be barista technique issues but it became clear that it was either incredible coincidence or reality. As I re-tested, it became clear that it was consistent and repeatable.
I'm sure this has some incredible implications when it comes to brew temp profiling. But right now I can't get my head around it.
Does it mean that a very, very stable and flat brew temp profile really is the answer? This would allow you to avoid those "off" temps and stay within a discrete sweet spot.
Or does it mean that a changing brew profile is the answer as it will allow you to combine positive attributes from various sweet spots across the top of the bell curve?
Right about now I really badly want to be able to control brew temp profile.
And, for the first time in a long time, I have consumed enough caffeine to give myself the sweaty creepy crawlies.
Andy... Greg... if you have a chance please please check and see if you can replicate this.
(Please note that the scores above are not in relation to some absolute scale - i.e are not compared to other coffees - but rather purely self-referential - i.e. compared to other shots in this experiment - and are thus totally arbitrary)