Author Topic: Hydrometer Temperature Accuracy  (Read 999 times)

Offline Kochhandwerk

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Hydrometer Temperature Accuracy
« on: May 10, 2017, 09:40:50 PM »
I brewed a Belgian Wit this weekend using 50% 2-row and 50% wheat flakes. I was in a bit of a mood because I knew I had a lot of other stuff to get done that day which probably caused most of my brew day issues.

I got my BIAB mash going with my volumes from BeerSmith. All seems to be going well.  Shooting for 1.046 OG.  Mash finishes, and I'm in a hurry and take a hydrometer reading at 110 degress Fahrenheit. Usually I cool down to 70-80, but like I said, I have a lot to get done so I roll with it and use a temperature converter tool. Even with the adjustment for high temp, I'm reading only 1.036. Since I boil 5 gallons and top off the ~1 gallon that evaporates, it really alarmed me that the gravity was much lower than 1.046.

I scramble and head to my LHBS (and fortunately they're my neighbors so they let me in before they were supposed to open) and grab some DME (I thought I had some handy, but nope, another mistake on my part). I get home, add the correct amount to adjust for gravity 1.046 for 5 gallons.  Not the focus, but I also added the DME in a rush and made a huge boilover mess on my stove that my ladyfriend had just made pristine.

So, I finish my boil, cool 'er down and add top off water to get 5 gallons.  Take a gravity reading, it says 1.056! I am pretty confident I did the DME math right.

SO, my question: does anybody know if your run-of-the-mill $10 float hydrometer has a limited temperature range where it is accurate?  Like I said, I used a gravity adjustment tool for temp, but I'm curious if the hydrometer loses precision far from its calibration temp (mine is 60 degrees F).  I was tempted to believe the reading at first because the wort looked very pale, but it also happened to be the lightest SRM beer I've made.

Offline lupulus

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Re: Hydrometer Temperature Accuracy
« Reply #1 on: May 10, 2017, 10:15:38 PM »
No. Hydrometers do not have a temperature range nor they lose precision.
Hydrometers have a temperature at which they were calibrated, so when you are measuring at another temperature just make sure you are measuring the temperature right and use the calibration correction from the current temperature to the calibration temperature.

Cheap hydrometers do have a problem, which is that the paper inside can slip.

Measure the density of water at the calibration temperature and if it is 1.000, the paper should be in the right place.
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Offline flars

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Re: Hydrometer Temperature Accuracy
« Reply #2 on: May 10, 2017, 10:20:56 PM »
Hydrometers are most accurate at the calibration temperature.  As the temperature of the wort increases the accuracy decreases.

Offline a10t2

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Re: Hydrometer Temperature Accuracy
« Reply #3 on: May 10, 2017, 10:36:57 PM »
A hydrometer can in principle be corrected to any temperature - the problem is that as the temperature differential rises, so does the rate of cooling of the sample. At 110°F it's cooling substantially (and unevenly) as you're trying to take a reading. That's why hot side readings are where refractometers shine.

A separate issue, but one that could explain your readings, is that it isn't really possible to get wort and water mixed homogeneously by hand. The yeast does a really good job of that, but stirring won't cut it.
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Offline denny

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Re: Hydrometer Temperature Accuracy
« Reply #4 on: May 10, 2017, 10:39:22 PM »
A hydrometer can in principle be corrected to any temperature - the problem is that as the temperature differential rises, so does the rate of cooling of the sample. At 110°F it's cooling substantially (and unevenly) as you're trying to take a reading. That's why hot side readings are where refractometers shine.

A separate issue, but one that could explain your readings, is that it isn't really possible to get wort and water mixed homogeneously by hand. The yeast does a really good job of that, but stirring won't cut it.

Agreed with both.  I'm almost positive your problem is the mixing.
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Offline Kochhandwerk

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Re: Hydrometer Temperature Accuracy
« Reply #5 on: May 11, 2017, 07:26:29 PM »
Thanks everybody. I usually do an average temperature from before I pour into my test flask and after I take the hydrometer reading but I may have only done the after reading this time. As one of you pointed out, the wort will cool at a faster rate the further it is from room temperature, so I probably screwed up and didn't adjust the gravity reading enough.  I did not know that I needed to mix the wort before reading to homogenize the mixture, so I will definitely do that from now on.

Offline 69franx

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Re: Hydrometer Temperature Accuracy
« Reply #6 on: May 11, 2017, 07:50:14 PM »
The best advice is to wait until boil gets going to take a post mash sample for OG. the boil should get it all pretty well mixed together. You can test gravity of separate runnings and then do some math (not sure of the math, likely averaging the gravities and volumes of the separate runnings) to predict the actual post mash OG, but once boil is going is the easier route
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Offline Lazy Ant Brewing

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Re: Hydrometer Temperature Accuracy
« Reply #7 on: May 11, 2017, 07:56:10 PM »
A hydrometer can in principle be corrected to any temperature - the problem is that as the temperature differential rises, so does the rate of cooling of the sample. At 110°F it's cooling substantially (and unevenly) as you're trying to take a reading. That's why hot side readings are where refractometers shine.

A separate issue, but one that could explain your readings, is that it isn't really possible to get wort and water mixed homogeneously by hand. The yeast does a really good job of that, but stirring won't cut it.

If it's difficult to get the wort and water mixed, how do you know that your refractometer is measuring an appropriate i.e. properly mixed sample?
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Offline denny

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Re: Hydrometer Temperature Accuracy
« Reply #8 on: May 11, 2017, 07:59:08 PM »
A hydrometer can in principle be corrected to any temperature - the problem is that as the temperature differential rises, so does the rate of cooling of the sample. At 110°F it's cooling substantially (and unevenly) as you're trying to take a reading. That's why hot side readings are where refractometers shine.

A separate issue, but one that could explain your readings, is that it isn't really possible to get wort and water mixed homogeneously by hand. The yeast does a really good job of that, but stirring won't cut it.

If it's difficult to get the wort and water mixed, how do you know that your refractometer is measuring an appropriate i.e. properly mixed sample?

He said hot side, which would be before water is added.
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Offline Lazy Ant Brewing

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Re: Hydrometer Temperature Accuracy
« Reply #9 on: May 12, 2017, 11:51:07 AM »
I'm confused.  The gentleman I quoted a10t2, said it could have affected the measurement.  You yourself said the problem was maybe the mixing.  Doesn't getting a correct reading from a refractometer depend on a homogeneous sample?

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Offline HoosierBrew

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Re: Hydrometer Temperature Accuracy
« Reply #10 on: May 12, 2017, 12:01:25 PM »
  Doesn't getting a correct reading from a refractometer depend on a homogeneous sample?





It does, but it's an easier thing to do for preboil and end boil readings because the turbulence of the boil does a good job of mixing the wort evenly. Turn off the heat though and wort begins to stratify pretty quickly. Personally, I use a refractometer for preboil OG readings and a hydrometer for FG readings.
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Offline Kochhandwerk

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Re: Hydrometer Temperature Accuracy
« Reply #11 on: May 12, 2017, 03:08:11 PM »
I use a hydrometer not a refractometer. I am guessing everybody that was referring to mixing was talking about samples for a refractometer and not a hydrometer sample which is much larger and presumably of much more uniform gravity.  I did not initially understand.

Offline denny

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Re: Hydrometer Temperature Accuracy
« Reply #12 on: May 12, 2017, 03:56:14 PM »
  Doesn't getting a correct reading from a refractometer depend on a homogeneous sample?





It does, but it's an easier thing to do for preboil and end boil readings because the turbulence of the boil does a good job of mixing the wort evenly. Turn off the heat though and wort begins to stratify pretty quickly. Personally, I use a refractometer for preboil OG readings and a hydrometer for FG readings.

Jon, have you seen that happen?
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Offline HoosierBrew

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Re: Hydrometer Temperature Accuracy
« Reply #13 on: May 12, 2017, 04:16:08 PM »
  Doesn't getting a correct reading from a refractometer depend on a homogeneous sample?





It does, but it's an easier thing to do for preboil and end boil readings because the turbulence of the boil does a good job of mixing the wort evenly. Turn off the heat though and wort begins to stratify pretty quickly. Personally, I use a refractometer for preboil OG readings and a hydrometer for FG readings.

Jon, have you seen that happen?


If I took a reading sample right at flameout, no. But after cooling started,  readings usually seemed more erratic. I attributed it to wort stratification. Nowadays I just take a preboil refractometer reading (actually a couple minutes into the boil to get good mixing) and a hydrometer FG reading, and call it good. It's by no means the only way to get there. Just my routine.
 
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Offline denny

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Re: Hydrometer Temperature Accuracy
« Reply #14 on: May 12, 2017, 04:27:59 PM »
If I took a reading sample right at flameout, no. But after cooling started,  readings usually seemed more erratic. I attributed it to wort stratification. Nowadays I just take a preboil refractometer reading (actually a couple minutes into the boil to get good mixing) and a hydrometer FG reading, and call it good. It's by no means the only way to get there. Just my routine.

Since I've heard this for years, I've tested it several times and never seen it happen.  Readings immediately post boil from various depths were the same as reading 15 min. and 1/2 hour later.  Now, that's iust me, which is why I'm looking for evidence that might contradict what I've seen.
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