Brew temperature and the weather

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Brew temperature and the weather

Postby IanClark on Tue Apr 07, 2009 8:14 am

Hi all,

I've been tracking a really fascinating trend over the past year with the boiler temps on our 8 Synessos across town. I'll explain what I've been encountering first - ultimately I'm curious if anyone has had a similar experience and if anyone has any idea what, in 'sciency" terms, is going on.

I'm writing from Ottawa, which for better or worse boasts the most extreme climate (temperature) of any capital city in the world. I've had to make dramatic temperature adjustments based on the temperature in the city on any given day. Essentially it works like this:

Above 15C: Temperature setpoint between 200F and 200.5F
Between 5C and 15C: Around 201F - 201.5F
Between 0C and 5C: 202-202.5F
Below freezing: 203F - 203.5F

These findings are the result of optimizing temperature to taste balance during the fall when temperatures started to drop, and once again throughout spring as temperatures rise (and fall.. and rise... and fall...). These findings are also uniform across the city. During Spring and Fall I'm resetting the temperatures on all machines up to a few times per week depending on weather patterns.

If our machines are set below the "recipes" listed above we get sour espresso, and anywhere above we get muddled flavour, low sweetness and general signs of overextraction. I'll note that the balanced shots in warm weather (200F) are way nicer than during cold weather (203F), but anything below 203F in the winter is horrifically sour.

The cool thing is this is completely consistent, so I can actually develop a brew temperature schedule based on the weather forecast (although I'd much rather just keep it constant!).

I've had a lot of fun tracking this problem! I'd also love to know what exactly is going on, mainly so that I can get balanced shots at 200F this coming Winter instead of being forced to pull good but never excellent shots at 203F.

Thanks if anyone has any experience or advise on where to look for the source of the phenomenon. I'm wondering if there is a change in alkalinity occurring? I'll have to grab a pH meter before Spring is over.

Ian
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Re: Brew temperature and the weather

Postby gscace on Tue Apr 07, 2009 10:36 am

Well inadequate temperature compensation of the PID controllers for ambient temperature changes would be one place to look. Also, is there a machine in your sphere of influence whose environmental conditions (temperature and humidity) do not change throughout the year that you could use as a reference? If that machine remained constant in its performance compared to the others, then I'd suspect controller issues. If that machine required setpoint changes as well I'd guess that the roasting and coffee storage conditions might have an effect, and I'd say that PID controller temperature compensation was OK. Humidity might also be a factor here, with colder outside conditions meaning drier inside conditions and less moisture within the coffee grinds.

-Greg (Sciency look and feel without the substance) Scace


IanClark wrote:Hi all,

I've been tracking a really fascinating trend over the past year with the boiler temps on our 8 Synessos across town. I'll explain what I've been encountering first - ultimately I'm curious if anyone has had a similar experience and if anyone has any idea what, in 'sciency" terms, is going on.

I'm writing from Ottawa, which for better or worse boasts the most extreme climate (temperature) of any capital city in the world. I've had to make dramatic temperature adjustments based on the temperature in the city on any given day. Essentially it works like this:

Above 15C: Temperature setpoint between 200F and 200.5F
Between 5C and 15C: Around 201F - 201.5F
Between 0C and 5C: 202-202.5F
Below freezing: 203F - 203.5F

These findings are the result of optimizing temperature to taste balance during the fall when temperatures started to drop, and once again throughout spring as temperatures rise (and fall.. and rise... and fall...). These findings are also uniform across the city. During Spring and Fall I'm resetting the temperatures on all machines up to a few times per week depending on weather patterns.

If our machines are set below the "recipes" listed above we get sour espresso, and anywhere above we get muddled flavour, low sweetness and general signs of overextraction. I'll note that the balanced shots in warm weather (200F) are way nicer than during cold weather (203F), but anything below 203F in the winter is horrifically sour.

The cool thing is this is completely consistent, so I can actually develop a brew temperature schedule based on the weather forecast (although I'd much rather just keep it constant!).

I've had a lot of fun tracking this problem! I'd also love to know what exactly is going on, mainly so that I can get balanced shots at 200F this coming Winter instead of being forced to pull good but never excellent shots at 203F.

Thanks if anyone has any experience or advise on where to look for the source of the phenomenon. I'm wondering if there is a change in alkalinity occurring? I'll have to grab a pH meter before Spring is over.

Ian
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Re: Brew temperature and the weather

Postby IanClark on Wed Apr 08, 2009 1:44 pm

Thanks for your thoughts Greg! (and yes, this situation is a very good reason why I should replace our broken scace device... if you're curious I left it in one of our shops overnight and it was returned to me with the thermocouple wire detached...)

I've definitely wondered the same things, but here's where I'm not sure...

Ambient temperature is pretty well constant as the machines are all indoors in more or less controlled environments. Would the PID have to correct for changes in the temperature of the water coming into the boiler? Perhaps so, but I'd imagine the HX would largely eliminate that variable as most water tends to enter the boiler above brew temperature. Also, the situation I've described applies to "working" machines as well as "standing" machines.

With respect to humidity, I suppose there could be a link however I'm not feeling convinced given that:

a) The same set point (within a 0.3F range) across 8 locations is required on two days with the same temperature range where one day is rainy and the other is dry.

b) Some of our shops have "living walls" that slightly increase the humidity of the store environment and these shops require the same set points (again within a 0.3F range) as those that do not have living walls, again strongly correlated with outdoor temperature

My next thought is to contact the City and inquire about known changes to water chemistry when the ambient temperature changes.

Thanks for the reply,

Ian
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Re: Brew temperature and the weather

Postby Phil Robertson on Wed Apr 08, 2009 9:54 pm

Hi Ian,

Well that's a head scratcher. Here's some random thoughts, based on some experiences we've had...

1) Is one of your controlled variables roasting? Specifically, have you experienced the need to run different temperatures for coffee roasted in the exact same batch? Could the ambient temperature be affecting the roasting and consequently the brewing?

2) What about the way that your roasted coffee is stored before it's used. Our coffee degases slower in the winter, as it's subjected to cooler conditions during transport. We've often had to run it hotter to compensate.

3) Consider measuring the ambient temperature, just to make sure that's not an issue. According to Mark, the Synesso does have cold junction compensation, but if it's not working properly for some reason, a degree shift in ambient temperature could cause a whole degree shift on the hot side of the thermocouple (i.e. in the boiler).

4) I'd suggest that you dig a bit more into the humidity. Check wunderground.com for dew point values for a particular day you have temperature data for (they have complete historical information). Use something like: http://www.hpc.ncep.noaa.gov/html/dewrh.shtml, to estimate indoor humidity. Or ideally, buy a humidity meter with data logging capability (that's what we ended up doing).

5) Measure your voltage. We had a big issue with power during periods of heavy load. Perhaps you're seeing additional loading caused by cooler ambient temperatures. We ended up installing buck-boosters to stabilize our voltage. Although, I would be shocked if you saw this issue across 8 machines.

6) If you don't have one already, consider buying a TDS meter. It's certainly not a comprehensive way to test water, but it's a great starting point. Our water TDS fluctuates all over the place; we've seen a 50ppm swing in a single day. Not necessary sure how this relates to temperature, but I wouldn't hold your breath waiting to get much out of the city regarding water (I couldn't seem to get much from the City of Calgary). Also, it's worth tasting the water from the group heads and the nearby tap on these various days. What kind of water conditioning do you use?

7) Send your scace to Greg to get fixed (via Espresso Parts NW), that's what we just did as our thermocouple snapped off too.

Good luck!
Phil

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Re: Brew temperature and the weather

Postby IanClark on Thu Apr 09, 2009 3:59 am

Thanks Phil, you rock. Many leads to work on now =)

It would be very interesting to track indoor humidity closely, so I'm going to have a go at that. I will also do some thorough ambient temperature logs as you and Greg advise.

I think I've eliminated storage/transportation (this was my first suspected cause) but I am going to continue tracking it.

With regards to TDS, I haven't been checking recently but in the not too distant past I did some considerable testing across town and never found a variance outside of 10ppm (we get 75ppm-85ppm across town). That's crazy that you have a swing of 50ppm in one day! Something to look out for no doubt.

At the moment we have some machines on cirqua taste & odour sediment/carbon filters and a couple that, for a short time, are still on a carbon/softener/sediment filter cartridge with mineralizer (which is not my preference... it makes our coffee taste a little too walnut-like). Machines on both systems follow the same temperature pattern.

Thanks again for the great advice.

Ian
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Re: Brew temperature and the weather

Postby IanClark on Thu Apr 09, 2009 6:55 am

With regards to humidity, would absolute humidity not be a more relevant variable than relative humidity?
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Re: Brew temperature and the weather

Postby Phil Robertson on Thu Apr 09, 2009 11:24 pm

Right, I agree. Absolute humidity is ultimately most important. The dew point is great to use because it's basically a measure of absolute humidity.

RH is just easier to work with (and we're more familiar with it's ranges). I'm assuming that we're discussing RH in the context of indoor temperatures (21 / 22 degrees C). With less than 20% RH considered arid and more than 50% considered humid, at 21/22 degrees C.

I'm a big believer in the affect of humidity on espresso extraction. I haven't gathered as much scientific research material as I'd like on the subject, but I have done a number of trials at various dew points. As always, controlling the plethora of other variables in espresso extraction is always a challenge.

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Re: Brew temperature and the weather

Postby Cosimo Libardo on Fri Apr 10, 2009 6:33 am

Hello Everybody, I am a new addition to Coffeed.com
I believe the problem you are describing should be more related to water temperature rather than room temperature: city water temperature fluctuates through the year, it is a small range of fluctuation (approx. 5°C), but in winter (especially in Ottawa) it could be annoying.
In a dynamic situation (brewing lots of coffees) the machine will not immediately compensate the change in temperature, also because in an espresso machine using dedicated boilers hot and cold water could not mix right away: it depends on how the boiler's cold water inlet is positioned and designed.
My suggestion would be to analyze water temperature and see if there is a fluctuation between seasons, also I would see if, after waiting 5 minutes from shot to shot, brewing temperature in fall / winter results to be higher.
It is just an idea.
Ciao,

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Re: Brew temperature and the weather

Postby gscace on Fri Apr 10, 2009 12:59 pm

Phil Robertson wrote:Right, I agree. Absolute humidity is ultimately most important. The dew point is great to use because it's basically a measure of absolute humidity.

RH is just easier to work with (and we're more familiar with it's ranges). I'm assuming that we're discussing RH in the context of indoor temperatures (21 / 22 degrees C). With less than 20% RH considered arid and more than 50% considered humid, at 21/22 degrees C.

I'm a big believer in the affect of humidity on espresso extraction. I haven't gathered as much scientific research material as I'd like on the subject, but I have done a number of trials at various dew points. As always, controlling the plethora of other variables in espresso extraction is always a challenge.


Yep. Water vapor concentration is what's important here. Use whatever unit you want, so absolute humidity is reasonable. RH and Dewpoint can be used to get water vapor concentration, but you have to know the saturation vapor pressure of water at the drybulb temperature in order to calculate concentration.

The idea that storage conditions affect the coffee is interesting and worth investigating. Water tends to diffuse into porous materials when it's humid and out of them when it's dry, reaching equilibrium in both cases.

-Greg (Actually, humidity research is my day job so I can quote chapter and verse on water in gasses any old time you wanna get an earful) Scace
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Re: Brew temperature and the weather

Postby gscace on Fri Apr 10, 2009 1:02 pm

Hey Cosimo!!

Welcome to Coffeed! Am I gonna see you in Atlanta next week?

Anyhoo, as I recall the Synesso machines preheat their water in the steam boiler before it goes to the brew boiler, so I'd expect that changes in inlet water temp would have very little affect on the brew temp.

-Greg


Cosimo Libardo wrote:Hello Everybody, I am a new addition to Coffeed.com
I believe the problem you are describing should be more related to water temperature rather than room temperature: city water temperature fluctuates through the year, it is a small range of fluctuation (approx. 5°C), but in winter (especially in Ottawa) it could be annoying.
In a dynamic situation (brewing lots of coffees) the machine will not immediately compensate the change in temperature, also because in an espresso machine using dedicated boilers hot and cold water could not mix right away: it depends on how the boiler's cold water inlet is positioned and designed.
My suggestion would be to analyze water temperature and see if there is a fluctuation between seasons, also I would see if, after waiting 5 minutes from shot to shot, brewing temperature in fall / winter results to be higher.
It is just an idea.
Ciao,

Cosimo Libardo
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Re: Brew temperature and the weather

Postby Cosimo Libardo on Sat Apr 11, 2009 8:19 am

Hi Greg,
yes I will be in Atlanta next week.
I have to abmit that I do not know well the hidraulic system of Synesso machines, but it seems quite unique that the phenomenon described happens in different locations.
I can tell you that in the past, on one of our older super automatic machines we had to analyze a similar phenomenon in Japan: our customer was continuously brewing long shots out of a 3,5lt. boiler, we found out that the cold incoming water was not "blending" completely with the hot water in the boiler, affecting the shot temperature. We have modified the boliler so that water would take a longer "pattern" through it having more time to mix and that solved it.
Again, I do not know if this could apply on a Synesso but it definitely has an impact on many boiler designs.
See you soon!
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Re: Brew temperature and the weather

Postby Phil Robertson on Sat Apr 11, 2009 8:53 am

I believe the problem you are describing should be more related to water temperature rather than room temperature: city water temperature fluctuates through the year, it is a small range of fluctuation (approx. 5°C), but in winter (especially in Ottawa) it could be annoying.
In a dynamic situation (brewing lots of coffees) the machine will not immediately compensate the change in temperature, also because in an espresso machine using dedicated boilers hot and cold water could not mix right away: it depends on how the boiler's cold water inlet is positioned and designed.
My suggestion would be to analyze water temperature and see if there is a fluctuation between seasons, also I would see if, after waiting 5 minutes from shot to shot, brewing temperature in fall / winter results to be higher.


Good point Cosimo. However, as Greg mentioned, the Synesso has a pre-heat path for the water entering the brew boiler, additionally the cold water inlet is mounted on the side of the brew boiler and the hot water pick-up is off the very top of the brew head / neck, so mixing affects should mitigated. Additionally, the Synesso element is way over-sized, so it keeps up pretty good, unless you're pulling copious amounts of water from the boiler. All that said, this is an issue (water inlet temperature) that would present itself across all eight machines on days that have colder outside temperatures, so it is very suspicious and worth investigating further....

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Re: Brew temperature and the weather

Postby IanClark on Mon Apr 13, 2009 7:13 am

Last week I started some serious data logging to go along with my temperature optimizations. I'm tracking indoor & outdoor temperature and RH (using the calculator Phil linked to) as well as all other major variables relevant to extraction, in addition to logging temperature and humidity on the roasting day and on the transportation day to see if there is a correlation there.

I'm also going to start taking measurements of inlet water temperature to see how much that sways. I think I have an SCAA pH meter around somewhere too...

It's going to take quite a while to develop enough data but hopefully I'll be able to better identify the cause of the phenomenon in the end. Sadly this will all have to wait until after Atlanta.

I love my job.

Thanks for the input.

Ian
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Re: Brew temperature and the weather

Postby Brent on Mon Apr 13, 2009 1:59 pm

Couple of late thoughts.

I have only really noticed temperature swings at home causing big shifts in grind changes. That was mainly one time when my wife managed to drop the inside temperature about 20 degrees in a few minutes. It took around 30 minutes to restore the temperature, and I was constantly adjusting the grind during that time.

The other thought that I had was what about the barometric pressure? What effect does this have?
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Re: Brew temperature and the weather

Postby IanClark on Fri Apr 24, 2009 10:48 am

I had a really exciting day of experimentation today:

Yesterday I optimized all of our machines for temperature and pressure, setting them all to a 203.5F brew set point for optimal balance and flavour clarity. These were all using the same batch of espresso (well, not exactly the same roasted batch but all espresso roasted the same day with the same electronically controlled and confirmed profile).

Yesterday's environmental conditions were:

Outside temperature (C): 12.17
Inside temperature (C): 22
Dew point (C): 4
Outoor Relative Humidity: 49.82
Indoor Relative Humidity: 26.74
Ideal brew temperature (F): 203.5

Again, all 7 machines I tested yesterday were pulling optimal shots at 203.2F to 203.5F

Today we started to roll over to a new roast date (4 days instead of 9 the previous day), but one shop I was at was still on the previous date. This gave me a great opportunity to see how both coffees would behave given today's environmental conditions. I was able to compare the required change in optimal brew temperature (recalling that just yesterday these were both optimal at 203.5) at one shop with the older coffee and one shop with the new coffee.

Today's conditions:

Outside temperature (C): 19.72
Inside temperature (C): 22.11
Dew point (C): 2
Outoor Relative Humidity: 30.76
Indoor Relative Humidity: 26.56
Ideal brew temperature (F): 201.2

Much to my delight, I was able to confirm that both coffees were tasting optimal at 201.2F whereas just yesterday Coffee # 1 had to be run at 203.5. In fact, while I was at one of the shops testing #1 we had a complaint that the coffee was bitter because I had not yet had a chance to adjust the temperature. After making the change to set point the customer enjoyed their replacement drink (meaning: I'm not just crazy).

So, let's have a look at the local variables:

Outdoor RH: + 19%
Indoor RH: No change

Outdoor temp: +7C (%change of 62.04%)
Indoor temp: No change

Roast date: 9 days : 4 days

Brew temperature set point: - 2.3F

Here are the roasting date environmental conditions:

Coffee 1 (9 days):

Mean temperature (C) 4
Dew point (C) -9
Avg humidity (RH) 36
Pressure (hPa) 1019.7

Coffee 2 (4 days):

Mean temperature (C) 8
Dew point (C) -5
Avg humidity (RH) 36
Pressure (hPa) 1020.43

Note that these are pretty similar.

Transportation date environmental conditions:

Coffee 1 (9 days):

Mean temperature (C) 7
Dew point (C) -8
Avg humidity (RH) 30
Pressure (hPa) 1022.82

Coffee 2 (4 days):

Mean temperature (C) 7
Dew point (C) 4
Avg humidity (RH) 86
Pressure (hPa) 1010.04

Note how much higher RH was for coffee #2! I'm not sure if this would have an impact on the coffee that is placed in valve bags on the roasting day though.

So, which variables have changed significantly?

Outdoor temperature: +62.04%
Outdoor RH: +19%
Transportation day RH : +56%

What can I draw from this?

I don't have information on water pH, inlet water temperature, actual brew temp (just working off PID settings until I get the scace fixed) or absolute humidity.

That said, given that both coffees required an identical change in boiler set point I think I can safely eliminate roasting & transportation environmental conditions. I'm going to continue tracking these variables to see if I can narrow things down a little more!
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Re: Brew temperature and the weather

Postby IanClark on Mon Apr 27, 2009 9:09 am

Brent wrote:The other thought that I had was what about the barometric pressure? What effect does this have?


Hi Brent,

Ambient pressure certainly influences the absolute humidity, hence influencing water activity in the coffee.

I'm looking at absolute humidity this morning and so far there's only a weak correlation to brew temperature. With full awareness that I don't have a lot of variables controlled, here are some data pairs:

Indoor Absolute Humidity (grains of water / lb) : Brew Temp Set Point

65.81 : 202
35.85 : 201.2
37.46 : 203.5
36.42 : 203
31.4 : 203.5
30.89 : 201.2
20.37 : 200.9
22.71 : 201.3
20.48 : 201.7
11.34 : 201

Still, the main climatic differences between last Friday and today using the same coffee but considerably more degassed are relative and absolute humidity (35.85gr/lb, 25.51% to 65.81gr/lb, 50%). The ideal brew temp set point increased by 0.8F today over last Friday, transforming a slightly sour and poorly flavoured cup into a sweet, fruity and balanced espresso.

Interesting, but so far not useful in predicting ideal brew temperatures.
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Re: Brew temperature and the weather

Postby gscace on Mon Apr 27, 2009 10:33 am

Howdee:

I just did a kwickee calculation to check on your numbers, and I'm curious how you got your RH and Dew-point numbers. For an outside temp of 19.7C and Dpt of 2, I get 31%RH. But for outside temp of 12 and dp of 4, I get 58%. Even so, it actually doesn't matter too much as i'll explain.

There are problems with the percentage thing. The temp and RH numbers may have changed by such and such percent, but...

In the case of the temp numbers, the fraction is based on the temperature scale that you chose to use. The Celcius scale uses the ice point as 0 and the atmospheric pressure boiling point as 100, which is really arbitrary. The behaviour of most temperature dependent things in the physical world is better predicted using absolute temperature, which is Degrees Celsius + 273.15 (the difference between the ice point and absolute Zero).

In the case of humidity, you're prolly better off using water vapor concentration, than using relative humidity. Relative humidity is the ratio of the actual amount of water vapor in the air (given in units of pressure - Pascal) to the maximum amount of water that can remain in the vapor phase at a specific temperature (the saturation vapor pressure - also given in Pa). If the outside temperature is at the dew-point temperature the RH is 100%. Since RH is given in percent, the ratio is multiplied by 100. At 50% RH, the air holds 50% of the water vapor that would be possible for it to hold at that specific temperature. The problem with RH is that it is dependent on absolute temperature. For your case of outside temp 12C, Dewpoint of 4C, the air could hold 1403 Pascal of water vapor, but actually holds 814 Pa. In the case of outside temp of 19.7C with dewpoint of 2C, the air can hold almost twice the water at 2299 Pa, but only holds 706 Pa. Actually the air in the colder case held more water vapor by 15%.

Additional comments - the inside environment temps and RH values that you observed were pretty constant. I'm guessing humidity ain't the source of your change, unless the coffee spends a lot of time outside, or the temp and humidity inside that you measured ain't what happens when the shop is busy.

I'm also interested in how your observed best brew temp squares with Emily Oak's recent post about the new vs old coffees and brewing temps. I also think you should gitcher Scace fixed and make the temp measurements at the group.

But you knew I was gonna say that sooner or later.

-Greg
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Re: Brew temperature and the weather

Postby gscace on Mon Apr 27, 2009 10:39 am

How lame. I'm replying to my own post to tell you that your experience of needing colder temps for newer coffee runs counter to the idea that Ms. Oak was curious about. Go figure.

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Re: Brew temperature and the weather

Postby IanClark on Mon Apr 27, 2009 11:40 am

Thanks Greg! Yes, I definitely should get my scace fixed. You will receive it shortly =P

I got my RH numbers from the calculator linked to earlier in the thread... I can't comment on its accuracy but that's interesting that there is some discrepency here...

EDIT: I just checked that calculation out and it was human error. The correct RH is 57.38%

Thanks for the explanation on RH and its relevance, I was actually wondering about this recently, which is why I started calculating absolute humidity (which so far hasn't yielded any strong correlations to ideal brew temp).

So far I haven't found the freshness of the coffee to be all that significant. Last week I was able to compare ideal temps on fresh coffee and less-fresh coffee and I found the same ideal temp set point for both. That said, this is all a bit uncontrolled and is hardly up to the standards the scientific method would demand. I'm trying to keep an open mind about everything so every suggestion is appreciated.

Edit: I just went over the relationship between roast freshness and ideal brew setting and did find something interesting:

4 days - 201.2
4 days - 201.3
4 days - 201.7
8 days - 202
8 days - 201.7
8 days - 203.5
8 days - 203
8 days - 200.9
8 days - 201
9 days 203.5
10 days - 201.2

The one constant here is that coffee very fresh has so far always preferred a lower temperature between 201 and 202. Getting above 7 days, the ideal temperatures fluctuate. That being noted, there is WAY too little data at this point (I've only been tracking this less than two weeks, with one of those weeks spent away in Atlanta) to draw any conclusions as there is so much else going on. This one will be interesting to follow over the coming weeks!
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Re: Brew temperature and the weather

Postby Brent on Mon Apr 27, 2009 3:13 pm

IanClark wrote:Ambient pressure certainly influences the absolute humidity, hence influencing water activity in the coffee.


we got a weather station thingy recently, and I have been watching the trends etc, which is quite interesting.

One thing I noted was that I have spotted some drastic drops in pressure, which among other things set one of the car alarms off.

which probably set off my question also... I use wunderground.com to store the data form the station and check that in relation to other stations in the wider area things are reading about right - this is particualrly so for pressure and humidity.
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Re: Brew temperature and the weather

Postby gscace on Tue Apr 28, 2009 10:00 am

Ian,

You might just have to log everything you can think of for a period of a couple months or so and see if there's anything that sticks out over time. Might take a good long while, but we ain't a goin nowhere.

-Greg
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Re: Brew temperature and the weather

Postby IanClark on Tue Apr 28, 2009 10:33 am

That's my plan =)
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Re: Brew temperature and the weather

Postby Michael Phillips on Tue Apr 28, 2009 9:00 pm

wow... I am dramatically outclassed by both the thought and effort you guys have put into this thread thus far but for some reason still feel compelled to comment. I work for the most part in one shop in Chicago and use a 3 group synesso. We have a cirqua system for water that is checked throughout the week to keep our water in spec. I am pretty involved with with keeping tabs on our espresso and usually dial it in at least 5 days a week if not more. I have found that the ideal temperature floats within about a 2 degree range and depending on how close an eye we keep on things that can even happen throughout the course of one day. It is unlikely to have swings that big in one day but not unheard of... In all of our shops we consider temp to be similar to grind when dialing in and there fore it gets adjusted somewhat frequently. I feel silly for having not tried to link its changes to anything so far but I"ll say for the most part it is because I am overwhelmed by the variables. Being that you have found your changes consistent across multiple machines and roasts really sounds environmental. I can say that just recently I did notice a somewhat consistent change to higher temps as we introduced a new origin to our blend. This is fascinating stuff Ian, I look forward to any results.
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Re: Brew temperature and the weather

Postby Alistair Durie on Wed Apr 29, 2009 12:21 am

I'm just wondering if what you're after here some formula that can be applied in a real world scenario. Such as reading a humidity increase and your barista drops the temperature by a degree and you get better shots? In the end all this measuring actually has some sort of benefit to your coffee? really? Is the goal of the experiment to try to make x + y = z?

Environmental shifts throughout the day seem to me enormously abstract measurements compared to those of colour, texture, flow rate, and taste of your coffee. Then there are beans themselves, the blend, the roasting, staling, grinding, all the variables that the barista is managing (or not) - all of these are seriously fast moving targets! Even if some formal science attempted to extract any discernible environmental measures to identify some trends over some long period, the coffee would be changing so fast that I think it would make all the data useless if reapplied. Environment can be tracked and responded to, but the largest factor - the coffee itself, remains truly elusive and will continue to surprise.

The requirement for human engagement to create great coffee is what makes it so fascinating and extraordinary.

Tell me the meaning of life and I'll tell you about your coffee.
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Re: Brew temperature and the weather

Postby Andy Schecter on Wed Apr 29, 2009 1:03 am

IanClark wrote:Ambient temperature is pretty well constant as the machines are all indoors in more or less controlled environments.


I'm playing with some numbers and wondering what you mean by "more or less" constant ambient temperature.

Below is a chart that makes some assumptions and is way oversimplified. But it suggests that when your dry coffee temperature goes down, the brew water temperature has to go up in order to maintain a constant brewing temperature in the portafilter.

The chart is a different take on the specific heat relationships originally outlined on page 30 of Scott Rao's book, The Professional Barista's Handbook.

Image
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