Brew temperature and the weather

elusive espresso... theorize, philosophize!

Re: Brew temperature and the weather

Postby IanClark on Wed Apr 29, 2009 2:05 pm

Hi Alistair -

I agree that it may be all for nought, however what got me on to this in the first place was seeing a very strong correlation between outdoor ambient temperature and a consistent ideal boiler set point across all of our shops on a given day (although this has become a little less clear upon further review!). This has lead me to believe that there may potentially be a limited number of variables that, if everything is is kept as constant as possible, I may be able to define, track and use to predict close-to ideal temps instead of reacting to them. At the risk of opening up a completely unrelated discussion on the realities of the labour market and the need to develop systems instead of relying entirely on human engagement, I simply don't think I have that option given the size and nature of our organization. Maybe in time.

Don't get me wrong though - I am a huge advocate for engagement and have witnessed what it can do for coffee and for our organization. In fact, my ultimate goal is to to identify a number of key variables that help us predict an ideal set point in the morning and have our staff check on these first thing - much like a baker would check on the humidity, tap water temperature, etc, before they start making bread in the morning. I think this would do wonders for their level of engagement, with resulting positive impacts on the attention and care going into coffee. In fact, there has already been a very positive impact just from me emailing ideal temps and having staff check the results.

I do see your point though, and perhaps it would be time better spent training enough espresso tasters within the company that know how to relate taste balance and flavour properties to necessary changes in brew temperature. This isn't at all unreasonable now that I consider it, but ultimately I'm a "systems" kind of guy and I'm much more inclined towards the approach of giving all 130+ of our baristas control over the coffee through well defined systems. If in the long term I end up with no meaningful results, then I'll have to rethink my approach! In the mean time this is a fun and very much enlightening experience to go through.

Andy, you make a great point - I hadn't thought of that variable. I've been checking the grinder's ambient temp with a thermocouple meter on every test. I said "more or less" before I started looking at this situation in detail, and there was a degree of ignorance in that statement I must admit!

There is in fact a variation due to the door being open on a cold day or a struggling A/C on a warm day. Looking back at the data I've gathered so far, there's no direct correlation between the fluctuations in ambient temperature I am seeing and the ideal set point, although it certainly may be influencing things. Just to pull data from one batch of coffee, I've got some shots being pulled at the same ideal boiler set point when the ambient temperature is 19C and 22C. What's both puzzling and encouraging is that I'm finding the same set point across all of our locations that, on a given day, all have minor variations in ambient temperature between them.

Mike - you're right, the variables are definitely overwhelming! It's quite fun =)
Ian Clark
Bridgehead
Ottawa, ON
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Re: Brew temperature and the weather

Postby justinemerson on Mon May 04, 2009 6:44 pm

interesting post, a great amount of information has been gathered and shared! We also have a few HX machines that we need to adjust as the weather cools down, just out of interest do your kgs/day go up significantly with the cold weather? and where are the ambient shop temps taken from? im still convinced that in our case its because the machine in general (group head specifically) can radiate more heat into the cafe when its cold, damp and the door is constantly being opened by more customers! pute theory tho.
justin
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Re: Brew temperature and the weather

Postby IanClark on Thu May 21, 2009 9:51 am

I'm pretty sure I've solved the mystery.

I ran a linear regression analysis of all the variables I was tracking. Granted I should have done multiple regression but I don't know how! From what little I know about regression I think these are still meaningful.

Anyway, here are the R Squared values for all the variables I was tracking:

Outdoor Temp: 0.021031444
Indoor Temp: 0.057406968
Dew Point: 0.100688152
Outdoor RH: 0.103337016
Indoor RH: 0.082390895
Ambient Pressure: 0.015590078
Absolute Humidity: 0.009350323
Days Off Roast: 0.057551578
Inlet Water Temperature: 0.218914186

As you can see, these were all totally irrelevant to the major changes I was seeing in ideal brew temp. I should note that of course they aren't irrelevant to temperature at a minor level - I was able to identify correlations between ideal temp and changes in ambient temperature and inlet water temperature, but these usually only influenced the ideal temperature by maybe 0.5F to 0.75F, as opposed to the 2F to 2.5F major fluctuations.

So, having determined that these environmental conditions were not relevant (I really didn't have to do a regression analysis... the ideal temperatures stabilized about a two weeks ago while the weather has continued to fluctuate wildly), I figured I would explore my initial hunch: water chemistry. Particularly alkalinity.

I got in touch with the Water Quality Supervisor with the City Government. She was very helpful and gave me information related to the seasonal changes in water chemistry - in particular changes that result from the "spring run off" .

In mid-March I started to notice the drop and fluctuation of ideal brew temperatures. At the same time the alkalinity of the city water begin to increase from about 25mg/L up to a peak of 40mg/L around April 12th, after which point it began to decrease again.

If you were to chart the trends in our ideal brew temperatures and the changes in city water alkalinity between Mid march and towards the end of April they would pretty well match in slope!

So, I'm pretty sure that solves the dilemma! Thanks to all for your input - this was quite an interesting undertaking. What still remains curious is that last summer our ideal temp was generally around 200F, whereas now it is still at about 203F! Well, I guess the coffees in the blend are different crop years so that might account for a difference.

Ian
Ian Clark
Bridgehead
Ottawa, ON
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Re: Brew temperature and the weather

Postby Dan Streetman on Thu May 21, 2009 8:42 pm

Ian,

that is a very interesting, and enlightening thing to find.

thanks for sharing
Dan Streetman
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