Mash temp and Thermometer issues

[HBCBrewmaster]

Sorry; that was unclear and I'll change the original post.

When weather services post barometric pressure, they are calibrating it to sea level to remove the amount of variation that is attributed to elevation change. Go to the wunderground.com and check the listing for Denver. Right now, the pressure is listed at 30.33 inHg, pretty much exactly what yours is.

I'm not sure of exactly why they do this, but that number doesn't reflect absolute atmospheric pressure. Instead, 30.33 inHg is how much pressure there would be if Denver were at sea level. The absolute number would be much lower. Meteorologists are tracking weather systems far up in the atmosphere and are interested in the numbers up there. Whether a column of high pressure or low pressure air happens at any given moment to be above death valley or Denver doesn't actually change the thing that they are interested in, which is atmospheric pressure at 20k feet.

aww crap. so what you're saying is that the pressure in my kitchen might not be the pressure stated by weather.com...or the wunderground.com for that matter either?...

 

[MalFet]

aww crap. so what you're saying is that the pressure in my kitchen might not be the pressure stated by weather.com...or the wunderground.com for that matter either?...

Nope.

Fortunately, there's a calculator here: http://www.srh.noaa.gov/epz/?n=wxcalc_stationpressure

 

[HBCBrewmaster]

Nope.

Fortunately, there's a calculator here: http://www.srh.noaa.gov/epz/?n=wxcalc_stationpressure

I tried using that calculator but I need to know my altimeter setting. This seems to be getting too complicated. Would you agree that the difference in pressure that exists at ground level where I am is negligible? After all If can be certain that a temperature reading of 152 F is actually somewhere between 151F and 153 F I'll be satisfied with that. At this point any way. I just don't think a variance of +/- 4degrees is acceptable but +/- 1 degree is.

 

[MalFet]

I tried using that calculator but I need to know my altimeter setting. This seems to be getting too complicated. Would you agree that the difference in pressure that exists at ground level where I am is negligible? After all If can be certain that a temperature reading of 152 F is actually somewhere between 151F and 153 F I'll be satisfied with that. At this point any way. I just don't think a variance of +/- 4degrees is acceptable but +/- 1 degree is.

The "altimeter setting" would (I believe) be the number you are getting for pressure from weather.com. So at 355 ft a weather report of 30.38 inHg is equivalent to 29.99 inHg. Based on that, your water should boil at 212.12 (i.e., almost exactly 212).

To answer your broader question, I certainly agree that this is a level of precision far beyond what is necessary or useful. At a high-ish elevation or in extreme weather situations it might make a difference, but not for your situation.

 

[HBCBrewmaster]

OK I did a new test with distilled water and tightened up the process a bit using some of the suggestions that you all had. Tomorrow, after I sober up from the Philly Beer Fest I will post my results.

 

[jkarp]

That first part is certainly true, and thanks for spotting the over-simplification. That said, 4 degrees is an enormous variation unlikely from simple weather based variation.

That depends. C or F?

It is VERY normal to see barometric pressure readings between 28 and 31 in-Hg. Check your local NOAA historical data if you doubt it. Even between those well rounded numbers, water's boiling point will vary 3 degrees Celsius, or over 4 degrees Fahrenheit. Sorry I did not give the scale in my previous post.

Here's a simple online boiling point calculator to play with.

 

[jkarp]

Perhaps you can explain that a bit more...I've always understood that boiling water at higher elevations means a lower boiling point. perhaps that has to do with pressure changes associated with higher altitudes.

Exactly. Water is stupid. It is not aware of what elevation it's at. Water held at 30 in-Hg on top of Mt. Everest will boil at 212F.

If that be the case then how do I adjust my expected boil point on any given day? It would seem that a brewer ought to nail that down before trying to make any calibrations. My elevation is 355 ft above sea level which I don't think would have any relevant impact on my boil temperature.

What does it matter? A boil is a boil. For brewers, as long as the boil temp is > 140F (the isomerization temp of alpha acids), we're just interested in the mechanical process of boiling - churning the wort, evaporation, etc. There's loads of world-class breweries here in CO and none give two thoughts to their boiling point. Mine is around 198F.

This also raises another interesting question about non digital thermometers...Could it perhaps be the case that the temperature reading at boiling given by my lab thermometer is being affected by the change in air pressure? In other words perhaps it's not the temperature at which water boils that's changing but rather the accuracy of my thermometer that is fluctuating with changes in atmospheric pressure? Could such a phenomenon affect lab and dial thermometers and not affect digital ones?

Shouldn't be anything different about digital or non-digital thermometers based on pressure. For any thermometer, at sea-level and a local barometric pressure of 30 in-Hg, they should read 212F at boiling in water.

 

[jkarp]

I tried using that calculator but I need to know my altimeter setting.

Call your local TV weatherman. As long as they're not on the air, they gladly give this data out. Just tell 'em you want the local non-elevation adjusted barometric pressure.

 

[MalFet]

That depends. C or F?

It is VERY normal to see barometric pressure readings between 28 and 31 in-Hg. Check your local NOAA historical data if you doubt it. Even between those well rounded numbers, water's boiling point will vary 3 degrees Celsius, or over 4 degrees Fahrenheit. Sorry I did not give the scale in my previous post.

Here's a simple online boiling point calculator to play with.

Oh, I see. You mean 4 degrees total range (i.e., (210º-214º). I think both the OP and I thought you were suggesting a four degree variation from a mean (212º±4º).

Even still, that seems very high. Do you have a link to the historical data? I couldn't find anything, but I'd be interested to see it. Doing a manual scan over the NOAA data in both my neighborhood and the OP's over the last few years, I found a maximum range on the order of 29.2 and 30.6, which is only 210.8ºF and 213.1ºF. Within that even, those extremes represented unusual days. 95% of days were within 29.6 and 30.3 (211.5ºF and 212.6ºF). But perhaps others aren't so lucky.

 

[jkarp]

Even still, that seems very high. Do you have a link to the historical data? I couldn't find anything, but I'd be interested to see it. Doing a manual scan over the NOAA data in both my neighborhood and the OP's over the last few years, I found a maximum range on the order of 29.2 and 30.6, which is only 210.8ºF and 213.1ºF. Within that even, those extremes represented unusual days. 95% of days were within 29.6 and 30.3 (211.5ºF and 212.6ºF). But perhaps others aren't so lucky.

Denver's been above 31 in-Hg and into the low 29s already this year and we're only 2 months in. Maybe our weather's more extreme?

http://www.thorntonweather.com/climatedatayearout.html

 

[HBCBrewmaster]

Exactly. Water is stupid. It is not aware of what elevation it's at. Water held at 30 in-Hg on top of Mt. Everest will boil at 212F.



What does it matter? A boil is a boil. For brewers, as long as the boil temp is > 140F (the isomerization temp of alpha acids), we're just interested in the mechanical process of boiling - churning the wort, evaporation, etc. There's loads of world-class breweries here in CO and none give two thoughts to their boiling point. Mine is around 198F.



Shouldn't be anything different about digital or non-digital thermometers based on pressure. For any thermometer, at sea-level and a local barometric pressure of 30 in-Hg, they should read 212F at boiling in water.

Thanks. To be clear, I am not concerned about the boiling temperature of water or wort except in so far as it helps me calibrate my thermometers.

 

[jkarp]

Thanks. To be clear, I am not concerned about the boiling temperature of water or wort except in so far as it helps me calibrate my thermometers.

But you were trying to use the former to achieve the latter, which is problematic. Again, buy a NIST traceable calibrated lab thermometer and calibrate to it, ideally around 150F where mash temps are so critical. As long as your dials are accurate around mash temps, it really doesn't matter if they're off a few degrees at boiling. Non-linear errors are not at all uncommon in thermometers.

 

[HBCBrewmaster]

But you were trying to use the former to achieve the latter, which is problematic. Again, buy a NIST traceable calibrated lab thermometer and calibrate to it, ideally around 150F where mash temps are so critical. As long as your dials are accurate around mash temps, it really doesn't matter if they're off a few degrees at boiling. Non-linear errors are not at all uncommon in thermometers.

Hey for nearly 5 hundred bucks it better be a good one! I'm not quite there yet but with the accuracy they claim that is likely where I'll end up. Thanks!

 

[HBCBrewmaster]

I did this test with a few changes from the first test. they are...
*I made sure that the thermometers were all 2 inches from the bottom of the pot.
*I used distilled water
*I recorded my observations of the temperatures at a specific time and repeated the process swapping out the three dial thermometers in succession resulting in a total of 10 readings for each dial thermometer and 30 readings for the digital thermometer and 30 for the lab thermometer.
*I tested in the range from 134F to boiling.

I won't bother listing all the numbers but briefly here is what I found.

The digital thermometer read 211 F at boiling and never exceeded that temperature throughout the entire process.

Of the three measurements at boiling, dial 1 was consistently at 210F, Dial 2 averaged 215.3F and dial 3 measured 212 on the nose each time.

Dial 1 measured an average of 2.2 F less than the digital,
Dial 2 was all over the place measuring higher and lower than the digital but was on average .3F higher than the digital
Dial 3 was never more than 1 degree from the digital and averaged exactly a zero F difference.

The Lab thermometer measured an average of 4.6F above the digital with several differences being 8 degrees above and one measurement being 5 degrees below. the mode was +4 degrees

My conclusions
1. Placement of the thermometer relative to the bottom of the pot is critical. That did not occur to me the first time.
2. The only way I could get the lab thermometer to agree with the digital was if I only had the very tip i.e. the first half inch touching the water. In my tests I held the lab thermometer with my hand at the same height above the bottom of the pot as the other thermometers. No doubt holding it with my hand caused greater variation in the measurements.
3. A lab thermometer is NOT the best choice for brewing
4. The dial thermometers were held in place by 12 gauge wire suspending them over the boiling water with the sensor part in the water at exactly the same depth as the digital probe. After observing the varying nature of their readings I can conclude that some are better than others even when they are all from the same manufacturer.
5. Knowing how atmospheric pressure can affect by boiling points is relatively unimportant compared with controllable factors such as depth, but was reassuring because I knew what to expect from an accurate thermometer. It is likely that the digital thermometer would have read a consistent 212 instead of 211 if the clip would have allowed me to push it further down into the pot. I will assume that the digital is accurate to within 1 degree.
6. As a result of #4 above I will recalibrate Dial # 1 and Dial # 2 using dial # 3 and the digital as benchmarks. I will install #3 in the mash tun, # 1 on the HLT and #2 on the boil pot. :rockin:

 

[jkarp]

At the risk of beating a dead horse (and please Dschuetz - tell me to STFU if you've had enough of me), why does what they're all reading at boiling matter?

It seems to me you're assuming that if you do a single-point calibration at boiling that you're all set. Dial thermometers in particular tend to exhibit non-linear errors. The further away from their calibration point, the greater the error. Ideally, you want to calibrate them as close as possible to the temperature range that's really important to you.

Recall back to your high-school science classes. Thermometers were tested against an ice water solution at 32F; NEVER against boiling water. A boiling liquid is far too dynamic. Simply by whirlpooling the water you can create several degree differences in the pot.

Lab thermometers are marked with the immersion depth for taking proper readings. For brewing, total immersion thermometers are best as you can get accurate readings deep in the mash. Using the wrong kind can lead to significant reading errors.

At this point, since you have one dial that's in the ball park at boiling, I would do a second test with it at 32F to check its linearity. If it reads reasonably close to 32F in a ice water solution, use it to recalibrate all the others at 150F. Then, don't worry about reading differences at the extremes.

 

[HBCBrewmaster]

At the risk of beating a dead horse (and please Dschuetz - tell me to STFU if you've had enough of me), why does what they're all reading at boiling matter?

It seems to me you're assuming that if you do a single-point calibration at boiling that you're all set. Dial thermometers in particular tend to exhibit non-linear errors. The further away from their calibration point, the greater the error. Ideally, you want to calibrate them as close as possible to the temperature range that's really important to you.

Recall back to your high-school science classes. Thermometers were tested against an ice water solution at 32F; NEVER against boiling water. A boiling liquid is far too dynamic. Simply by whirlpooling the water you can create several degree differences in the pot.

Lab thermometers are marked with the immersion depth for taking proper readings. For brewing, total immersion thermometers are best as you can get accurate readings deep in the mash. Using the wrong kind can lead to significant reading errors.

At this point, since you have one dial that's in the ball park at boiling, I would do a second test with it at 32F to check its linearity. If it reads reasonably close to 32F in a ice water solution, use it to recalibrate all the others at 150F. Then, don't worry about reading differences at the extremes.

I would only tell you to STFU if you were saying stupid things which you are definitely not. But to address some of the issues you raise, I did test the thermometers against themselves through a range of temperatures from 130F to boiling. The only reason to go to boiling was to see how they responded at a temperature point that I was very confident should be very close to a known value. Prior to beginning the test I wasn't even sure I had a reliable digital thermometer. Now I have more confidence in it. I made 18 tests from 179-boiling (6 for each dial) and 12 tests from 130 to 200 (4 for each dial) and at that point I was sick of doing it and had to get ready for the Philly Craft Beer Fest!!! Ootherwise I would have made several more readings in the mashing range. The Lab thermometer does have an immersion line marked and that is exactly where I did my best to hold it however my hand is not as steady as a pot clip or the wires I used to hold the other ones. Regarding the ice water bath I'm afraid that will be impossible with the dial thermometers because their lowest mark is 65 f. These are the ones that come with a Blichmann boilermaker. AND the cheapish digital just reads "Low temp" at anything below 33F so that's not much use either. But your point is well taken about calibrating to the mash range and that is just what I'll do. After I get my Therma pen I will use that and the cheapish digital probe and the reliable dial thermometer to calibrate all three dial thermometers to be accurate at 152F. By doing this, I think (my hope is any way) I will get all three linear representations of the dial thermometers to intersect at the same point. That point being 152F, plus or minus 1 degree

 

[jkarp]

Oh wow, never noticed the Blichmann ones bottomed out at 65. NOW I see your predicament...

 

[MalFet]

Cool stuff Dschuetz. I am reminded of why all my lab monkey/research science grad student friends hate their lives so much.

The fact that you got more consistent results is both good news and bad news. Boiling water would have helped you figure out which of your thermometers were off by 7 degrees, but won't tell you which of them might be off by the more modest margins you are seeing now. The good news is that now you can laugh all the folk who have digital displays on their mash tuns spitting out measurements to the hundredth of a degree and explain to them the difference between accuracy and precision.

Jkarp's suggestions are good ones, and now that you've got a thermapen coming you will with any luck have a more reliable baseline against which to calibrate everything else. Keep us posted!

 

[HBCBrewmaster]

Will do MalFet. Just to point something out however, something I didn't mention in my conclusions as clearly as I should, I am very confident based on my observations that the reason my dials were all reading 7 or so degrees higher than the digital is because I was not paying attention to their depth in the water bath as compared to the digitals probe. I remember that at the time I was more concerned with making sure that they were submerged to the depth at which t they would connect to the pots they attach to. This meant that they were about 3/4 of an inch lower toward the bottom of the pot and much closer, relatively speaking, to the flame radiating underneath the pot. all three dial thermometers were about on average 7 degrees lower than they were on the first test.
And thanks for the compliment as well as all your input, without which I would still be scratching my head in confusion.
D

 

[lemy]

I had much the same experience with several Taylors. They are now residing somewhere in a landfill. The most reliable thermometers are the traceable glass lab thermometers. I have this one and it is go to benchmark when checking/calibrating the others I have:

http://www.carolina.com/product/equ...).do?keyword=745416&sortby=bestMatches&page=1

Exactly what I have been looking for Thanks for the link!

 

[lemy]

So, I brewed many batches using unreliable thermometers (common walmart digital meat thermometer). I used two separate thermometer's and later compared both with ice water and both gave me different temperatures. It really explains a lot of my low temp mashing and light body beers.

I bit the bullet after much research and purchased a cole-parmer thermocouple. The sensors can be purchsed from ebay for $3.00 - $6.00 each... I really think this is the way to go and am extremely happy with my purchase as it puts an end to a lot of frustration.

I believe a thermocouple, is as important to the home brew machine as is a heat exchanger or an auto-siphon.

The whole thing for under $50.00:
http://www.coleparmer.com/catalog/product_view.asp?sku=9121045&pfx=

 

[HBCBrewmaster]

That is a pretty cool thermometer. How do you use it? By that I mean, how/where do you place it in your mash tun? I have found that the $20.00 digital oven thermometer is very acurate. I check it against a NIST Thermapen. And after all my calibrations and comparisons I feel very confident in how it reads. But I've also found that by placing it in different locations in my MT I can get very different readings. I pull on a Blichmann elbow length brewing glove and shove the probe all the way to the middle center of my 20 gallon mash and it reads one thing, then I move it to the top left and I get another then the top right and another. (I circulate with a modified rims system- a March pump and a propane burner as the heat source) Usually it's within about 5 degrees which is not really the acuracy I'm looking for. But, when I take a quick average and compare it to the dial on the Boilermaker it gets to within 2 or 3 degrees of agreement. Then I make a judgement to raise or lower the flame. It's not easy but I feel that because I can measurre the temp in any location I want I can get a better feel for what the real temp is. I'd like to see if that company makes a 2 sensor model so I can place the sensors in different places at once and doubble my data collection.

 

[lemy]

My big problem was that u was using two thermometers and one was way off. So I would start with water way too low, typically, and end up decocting.

My other problem was not really knowing, or believing that my actual mash temp was correct.

The thermocouple comes with an NIST cert saying it was calibrated, so I have more faith in that (so Many things in life come down to a simple question of faith)

The other thing is the digital meat therms are not water tight and if you submerge them past the metal probe they can start giving funky readings. I actually had that happen and read about it in these forums.


I Do understand there are hot and cold spots in the mash tun, but I guess we can only do what we can do, because i dont know a way around that one. I may look into a rims at some point.

 

[HBCBrewmaster]

I wanted to add this video link from Thermoworks where I eventually bought my thermapen. I do love my thermapen. For home brewing I use it to quickly determine the temperature of my mash (within 6 inches from the surface) the temperature of wort when I take a gravity reading, the temperature of the water coming out of my fawcet so I know about how low I can reasonably expect my counterflow wort chiller to take the temperature of my wort, and I even use it to check the ambient temperature of my basement. It is awesome. To illustrate just how reliable this thing is, I can take my body temperature by touching the tip (which is like touching the tip of a sharp knitting needle) and within a few seconds I get an accurate body temp. I also use it all the time when I cook meat. I love it.
Dave

 

[TrubDog]

Hey - I just ran across this thread and it's great! The dial thermometer that came with my Bayou Classic was 10 degrees off (low) when I compared it to my glass floater and my digital instant read. That explains my crappy efficiency on my first two batches. I now use two thermometers to validate my mash temps.

 

[oakbarn]

Use the lab thermometer to calibrate the digital. If you want 151 degree mash, heat some water to 151 with the lab one, check the temp of the digital, if it reads 154, and then just apply that correction. I have found the cheap ones unreliable but usable if I calibrate and use 154 as 151. As a side note, I have a 40 gal Mash Tun with 2 thermometers, on higher than the other. They normally read different by several degrees and they have been calibrated together. I use a Herms system, and the higher one is normally higher temp (mash) than the lower one. They eventually come together after about an hour of recirculation. You should recalibrate on a regular basis.

 

[HBCBrewmaster]

I'll respectfully disagree with oakbarn. If you mean a glass lab thermometer, those are not very good in my experience. (read this thread) while they may be accurate, they are very particular about the depth that they are plunged into the medium being measured and worst of all they are very slow. A digital NIST thermometer like that from ThermoWorks.com - Home of the Thermapen is very fast and can be relied uppon for accuracy. If you want to be accurate to within +/- one degree F a lab thermometer won't get you there without a lot of hassle and doubt.

 

[homebrewers_haven]

I work in the food service industry where probe thermometers are common. I use an Atkins brand probe and it works great--and the probes are replaceable. They are a bit spendy but should last forever...I've had mine for yearssssss.

Here is what I have-- http://www.google.com/products/cata...=X&ei=04QtT7WANs_ciQKkxMzJCg&ved=0CK0BEPICMAk