Lesson learned about being cheap

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Lesson learned about being cheap

Postby budvar » Wed Feb 13, 2008 12:58 pm

I feel I should share my mistakes with others, so you won't make the same errors I made.

In the quest to obtain the perfect strike temp, I found my problem and it's not the software, it was my digital thermometer.

I was using 2 thermometers I picked up in a big box store's cooking section and one was 7 degrees off and the other was 1 degree off.

How can you find out if your thermometer is accurate, easy, place it in a cup of ice water and it should read 32 degrees.

If I would only have know I could of saved a lot of hair pulling.
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Re: Lesson learned about being cheap

Postby jeff » Wed Feb 13, 2008 2:05 pm

budvar wrote:one was 7 degrees off
Yikes :shock:
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Postby dasein668 » Wed Feb 13, 2008 3:27 pm

Test it in boiling water, too. Mine is accurate at freezing, but off by 3 degrees at the boiling point. I adjust by 2 degrees at mash temps, and call it good.
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Postby budvar » Thu Feb 14, 2008 1:04 am

When it comes to boiling water you have to take alltitude into account. Ice water is the same anywhere.
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Postby dasein668 » Thu Feb 14, 2008 8:16 pm

budvar wrote:When it comes to boiling water you have to take alltitude into account. Ice water is the same anywhere.


True, but that is easy to do. (I should have remembered to point that out, though! Sometimes I forget because I live at about 50ft of altitude, which only accounts for less than a tenth of a degree.) There are lots of online calculators such as this one here.
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thermometer calibration

Postby slothrob » Fri Feb 15, 2008 10:14 am

It's good to check at both ends of the temperature scale, anyway, if you don'thave a way to check at mashing temperatures, since thermometers can be accurate at one end and not the other. If they are correct, or off by the same amount, at both ends, there's a good chance they'll be accurate in the middle.
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Barimetric Pressure can be more important than elevation

Postby billvelek » Fri Feb 15, 2008 11:06 am

dasein668 wrote:snip ... There are lots of online calculators such as this one here.
I like this one better -- http://www.thermoworks.com/software/bpcalc.html -- because it has a greater range on the barimetric values. I checked the weather history for my zip code for the past two years for pressures, and found that our minimum was 29.24 and our maximum was 31.18, but when I entered 31.18 into the calculator at your link an error message said: "The calculator can only calculate for pressures between 0.2 and 30.3inHg. Please try again." Anyway, I was very surprised to see that the barimetric pressure makes even more of a difference than altitude -- almost five times as much of a difference. Here is my data for my 2-year minimum and maximum barimetric pressures and for both S.L. (sea level altitude = 0) and my altitude of 361 feet:
31.18 + S.L. = 214.04
31.18 + 361' = 213.40 : 214.04-213.40= 0.64
29.24 + S.L. = 210.89
29.24 + 361' = 210.24 : 210.89-210.24= 0.65
214.04-210.89= 3.15 : 213.40-210.24= 3.16

As you can see, the difference between S.L. and 361' is just .64 or .65 degrees, whereas the difference between a pressure of 31.18 and 29.24 is 3.15 or 3.16 degrees. Next brew session, I'm going to check our barimetric pressure and recalibrate my thermometer. This also makes me wonder if the BTP software needs to take pressure into consideration rather than altitude (the 'Schedule' tab has an entry for 'Elevation'). It's not hard to check on current barimetric pressure for a location; I just click on my weather station icon in my programs tray.

Here is the site I used to check pressures over the past 2 years -- http://www.wunderground.com/history/air ... .html?MR=1 -- enter your zip code in the upper left corner, go to history, select the 'monthly' tab, and then use the 'previous month' and 'next month' controls in the upper corners of each monthly summary.

Of course, I don't know how vital those differences could be to BTP, but if it's important enough to insert 'Elevation' then it seems to me that it should be important enough to insert 'Barimetric Pressure' if it could have five times the influence.

Cheers.

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Postby budvar » Fri Feb 15, 2008 12:38 pm

The real question then becomes how do you test for accuracy at mashing temps? Because it's going to boil regaurdless of where your at.

Do you think the big boys takes all that into account? With everything they do I wouldn't be surprised.
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Thermometer accuracy

Postby billvelek » Fri Feb 15, 2008 1:14 pm

budvar wrote:The real question then becomes how do you test for accuracy at mashing temps? Because it's going to boil regaurdless of where your at.

Do you think the big boys takes all that into account? With everything they do I wouldn't be surprised.
Right, but that's why you need to accurately determine the boiling temperature for your location using barometric pressure and elevation, and then see what you thermometer reads. Then, in order to compensate for any differences, I think it depends on the type of thermometer you have and how it is off. If it's off the same amount at both freezing and at boiling, then it is strictly a linear adjustment of adding or subtracting the difference regardless of temp. If there is a difference in the delta at each end, then I think you can probably extrapolate with no problem to arrive at a proportionate adjustment which will vary depending upon your temperature point. That sounds like a lot of bother, but just remember that you only need to do this once for each typcial temp that you use, and then record that info for reference during future brewing sessions. And I'm sure the big breweries calibrate their equipment.

Cheers.

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Postby budvar » Fri Feb 15, 2008 4:16 pm

I'm only 12 mister
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