Scientific Paper: Brewing Temperature and the Sensory Profile of Brewed Coffee

Coffee preparation techniques besides espresso like pourover.
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TomC
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#1: Post by TomC »

https://sca.coffee/sca-news/read/just-p ... wed-coffee

UC Davis Coffee Center has a new paper out that was published in Scientific Reports, evaluating the results of some 3 years of study into temperature of a filter brewed coffee, its sensory differences and lack thereof, when brew ratio and extraction are kept constant.

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yakster
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#2: Post by yakster »

Surprising result, thanks for posting this. It would be interesting to see this repeated for a natural processed coffee from Ethiopia.

I also found this quote from the paper surprising regarding cafes: "At least one estimate indicates that energy usage in a café accounts for 45% of the overall carbon dioxide emissions of brewed coffee production, even when accounting for all other steps including the agronomy at the farm, the post-harvest processing, and the roasting [33]."
-Chris

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another_jim
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#3: Post by another_jim »

The paper deals in minute differences. Given my everyday experience, I would be very surprised indeed if I and everyone else could not tell apart two brews with identical extraction yields and brew strengths, one ground course and steeped at 95C in a french press, the other ground fine and slow drip brewed at 85C.

If you are looking for the effect of a variable; it's good practice to actually vary it. Especially when you use a brewer that isn't exactly a precision instrument.
Jim Schulman

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CarefreeBuzzBuzz
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#4: Post by CarefreeBuzzBuzz »

another_jim wrote:The paper deals in minute differences. Given my everyday experience, I would be very surprised indeed if I and everyone else could not tell apart two brews with identical extraction yields and brew strengths, one ground course and steeped at 95C in a french press, the other ground fine and slow drip brewed at 85C.

If you are looking for the effect of a variable; it's good practice to actually vary it. Especially when you use a brewer that isn't exactly a precision instrument.

Not sure the average person can meet the prep requirements.
we have to be careful in our terminology: the brew strength (as measured by TDS) and the extraction yield can be either dependent or independent variables, depending on what experiment you're talking about. For example you can change the grind size for several different brews, then measure the resulting TDS in each. In that experiment the grind size is the independent variable and the TDS is the dependent variable. For our work, we carefully changed several parameters, including the grind size and flow rate, to achieve a specific TDS, and we then measured the resulting sensory profile at that TDS. In this case, the independent variable is the TDS, and the sensory attributes are the dependent variables. Brew time, grind size, and brew temperature are all tremendously important for coffee brewing-but our data strongly indicate that they are important because they affect what TDS and extraction percentage you get, not because they intrinsically alter the coffee (at least over the range of temperatures tested here). Again, it's the destination that matters, not the exact route you took to get there.
CarefreeBuzzBuzz
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DamianWarS

#5: Post by DamianWarS »

another_jim wrote:The paper deals in minute differences. Given my everyday experience, I would be very surprised indeed if I and everyone else could not tell apart two brews with identical extraction yields and brew strengths, one ground course and steeped at 95C in a french press, the other ground fine and slow drip brewed at 85C.

If you are looking for the effect of a variable; it's good practice to actually vary it. Especially when you use a brewer that isn't exactly a precision instrument.
I only read he SCA interview (not the actual study) but it seems to be regarding drip (and more specific with batch brewing) and not suggesting that other brew methods with the same TDS taste the same. I'm more wondering why they didn't test hotter temps as well like boil/off the boil. But perhaps their batch brewer which was a Curtis G4 doesn't do boiling.

Like you I would have been more interested in some more varied testing. Breville helped to fund it (I guess) so you think at least they could have tried a Breville batch brewer.

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another_jim
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#6: Post by another_jim »

CarefreeBuzzBuzz wrote: Not sure the average person can meet the prep requirements.
You're simply repeating my point. If you contend that two brews with equal TDS and EYs will taste the same; then you falsify that contention by making two really different preps with the same TDS and EY, not two preps that are in nearly indistinguishable on every other variable.

Given our fruitful discussion guidelines, I will not comment on the general standard of this lab's papers, nor on why anyone would pay attention to them. But I can't resist saying that we are living in truthy times; and it seems the SCA has gone all in on being sciency.
Jim Schulman

DamianWarS

#7: Post by DamianWarS »

yakster wrote:Surprising result, thanks for posting this. It would be interesting to see this repeated for a natural processed coffee from Ethiopia.

I also found this quote from the paper surprising regarding cafes: "At least one estimate indicates that energy usage in a café accounts for 45% of the overall carbon dioxide emissions of brewed coffee production, even when accounting for all other steps including the agronomy at the farm, the post-harvest processing, and the roasting [33]."
With cafes I think the worst comes down to how water is heated and then how much of it is wasted. There is a web app made by a scientist Steven Abbott with Barista Hustle and it shows that brewing alone contributes to 45% of the overall carbon footprint of coffee.

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CarefreeBuzzBuzz
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#8: Post by CarefreeBuzzBuzz »

another_jim wrote:You're simply repeating my point. If you contend that two brews with equal TDS and EYs will taste the same; then you falsify that contention by making two really different preps with the same TDS and EY, not two preps that are in nearly indistinguishable on every other variable.

Given our fruitful discussion guidelines, I will not comment on the general standard of this lab's papers, nor on why anyone would pay attention to them. But I can't resist saying that we are living in truthy times; and it seems the SCA has gone all in on being sciency.

Jim, I think its super important that you speak up. This is UC Davis, and their coffee program, living off their wine program. If there are issues as you see them by all means speak up and send them to Davis as well. Otherwise people will just get #fakenews and that's not what the coffee community really wants.
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Peppersass
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#9: Post by Peppersass »

another_jim wrote: ... I would be very surprised indeed if I and everyone else could not tell apart two brews with identical extraction yields and brew strengths, one ground course and steeped at 95C in a french press, the other ground fine and slow drip brewed at 85C.
I get that you're saying identical TDS and EY wouldn't result in identical taste between 95C french press and 85C slow drip, but you've introduced another variable: immersion brewing versus drip brewing, not to mention the dramatically different body/mouthfeel between those methods that might influence tasters.

The study used the same brewers/methodology at each tested temperature:
All coffees were brewed in Curtis G4 Single 1.0 Gal brewers (Model: G4TP2S63A3100, Wilbur Curtis Co., Montebello, CA, USA), with a flat bottomed brew basket and disposable paper filters.
I'm not saying that the study is right, just that they took pains to compare only the temperature differences.

For me, the shocking conclusion of this study is not so much that temperature differences don't matter, but that grind size differences don't matter, provided other parameters (e.g., temperature) are adjusted to keep TDS constant. That flies in the face of many discussions here on HB.

The question that's always in my mind, that I don't believe anyone has answered, is this: "What dissolved compounds from the grounds are present in the cup, and in what respective concentrations and or ratios, and how does that affect perceived taste?" If we can accurately measure that, then we can determine the impacts on taste of varietal, terroir, cultivation methods, processing methods, roasting levels/methods, and brew methods.

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another_jim
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#10: Post by another_jim »

They are claiming nothing but EY and TDS matters .... (if you don't vary the temperature by more than 3C and he grind by three clicks and the brewer not at all.)

It's BS either way. The independent variables, grind and temperature, constrained by constant EY and TDS, are so invariant in the test that most people would not taste the difference even if the EY and TDS had not been controlled. And if these independent variables had been greatly varied, the constraint of a constant TDS and EY would not matter.

Ask, why are they using Curtis brewers instead of some easily controlled immersion process where brew time and temp can be changed over a wide range. Do this at home, and convince yourself that once brewing temperatures fall below 88C or go above 97C, the mix of compounds extracted is so changed compared to the normal range of brewing temperatures, that TDS and EY cease to matter all that much. Pressure brewing, e.g. espresso also changes the taste; although long P/I times at low pressure change the taste back to a more brewed profile.

We know all this brewing stuff inside out; so why do we take this commercialized trivia-science seriously? I read Science News and Science Daily very regularly. PR people are swarming all over the abstract releases, and even with peer reviewed papers, ones BS detectors need to be very wide open nowadays. About half the stuff I read on those sites is trivia (like this paper) or me-too entries in hot fields. The good part of having lots of STEM people is lots of new research, The bad part is that more and more of it is noise.

In the fields we know, it is up to us to denounce trivia like this, not to bow down blindly to everything that describes itself as a "Scientific Paper" We are the peers, and we should be reviewing.
Jim Schulman