Innacurate Hydrometer

I was skeptical of a FG reading on my Irish Stout at bottling so I took a reading of water at 60F and it read 1.005. It is the basic triple scale hydrometer that came with my first brewing kit. Can I just subtract 5 points from all readings, or do I need a new hydrometer? Is there a more accurate hydrometer if I get a new one?

Look into getting a refractometer...you wont regret it. I would probably just get a new hydrometer if not. Also, use distilled water to check your current one before you write it off as being bad. Dissolved salts and other compounds are measured by the hydrometer as well and may be noticable in your tap water.

wobrien said:

I was skeptical of a FG reading on my Irish Stout at bottling so I took a reading of water at 60F and it read 1.005. It is the basic triple scale hydrometer that came with my first brewing kit. Can I just subtract 5 points from all readings, or do I need a new hydrometer? Is there a more accurate hydrometer if I get a new one?

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Toss it and get a new one. Refractometers are great, though I still use a hydro to verify FG (I like tasting it&#128521.

wobrien said:

I was skeptical of a FG reading on my Irish Stout at bottling so I took a reading of water at 60F and it read 1.005. It is the basic triple scale hydrometer that came with my first brewing kit. Can I just subtract 5 points from all readings, or do I need a new hydrometer? Is there a more accurate hydrometer if I get a new one?

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the scale is linear, so yes, you can just subtract 0.005 from your readings

I'll try a reading in distilled water when I get a chance. Not ready to spend the money for a refractometer, but there has to be a more accurate hydrometer, no? I feel like the paper glued inside the tube could easily shift.

mb2696 said:

the scale is linear, so yes, you can just subtract 0.005 from your readings

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Nope. It is not linear. The error can become greater as the gravity increases. I've done some signficant testing on this. I'll find the results and post, but I have (had) 3 hydrometers and one of them was bad.

Throw the hydrometer away.

[edit]

Conclusion: Hydro #2 got thrown away. It had error that was definitely NOT linear. Measured same samples with a refractometer and 3 hydrometers. The data:

Whether it's linear or not will depend on why it's inaccurate. If it's because the paper with the scale on it has shifted inside the glass tube, then it'll just be an offset. If it's because the tube is the wrong diameter (or is not cylindrical), then it will be more than an offset (though not necessarily nonlinear---if it were conical instead of cylindrical, it'd be linear, but not just an offset).

zeg said:

Whether it's linear or not will depend on why it's inaccurate. If it's because the paper with the scale on it has shifted inside the glass tube, then it'll just be an offset. If it's because the tube is the wrong diameter (or is not cylindrical), then it will be more than an offset (though not necessarily nonlinear---if it were conical instead of cylindrical, it'd be linear, but not just an offset).

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Great point zeg -- thank you for pointing that out. 1) I was misapplying the term linear and 2) I hadn't even thought of the shape of the glass!

You're only off by 5 points. My bet is that it is due to dissolved stuff in your water. Distilled water should read spot on, but not tap water. Get a second hydrometer and see if the readings match.

You could standardize it by dissolving sugar in water at different concentrations and then seeing what the specific gravity reads. I suppose that's a lot of work for a $5 item.

If all you are interested in is determining %abv, that's calculated by the difference of two readings. If the hydrometer is off in the same direction (systematic error), the errors should cancel when subtracting. I'd be more concerned if I had 2 hydrometers that read differently than each other than if my single hydrometer read off what I expected.

passedpawn said:

Nope. It is not linear. The error can become greater as the gravity increases. I've done some signficant testing on this. I'll find the results and post, but I have (had) 3 hydrometers and one of them was bad.

Throw the hydrometer away.

[edit]

Conclusion: Hydro #2 got thrown away. It had error that was definitely NOT linear. Measured same samples with a refractometer and 3 hydrometers. The data:

Refractometer: Water: 1.000 Test Solution: 1.100 (as much as I could discern the fine lines)
Hydro 1: Water: 1.000 Test Solution: 1.101
Hydro 2: Water: 1.002 Test Solution: 1.111
Hydro 3: Water: 1.000 Test Solution: 1.100​

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I did misspeak by saying that since it's linear it's just an offset.

However, for the reasons zeg pointed out, just because "the error can become greater as the gravity increases" does not mean it is not linear. It could simply be that the glass is the wrong diameter in which case the correction would be a scaling AND offset, which is still linear.

In your experiment I would agree that it looks like the correction for hydro 2 it not simply an offset. However, this does not mean that a hydro should be thrown out if it doesn't read 1.000 in water. You need a second high-ish gravity verification solution (like what you've done). On the other hand, it's $5 for a new one, so maybe it's not worth the time?

I would not throw it away. That's exactly how you calibrate a hydrometer, using 60F distilled water. If it is too high by .005, then you know to subtract that from each reading. BTW refractometers are not all they are cracked up to be in terms of accuracy. They also require a conversion factor when using them with wort, and that conversion factor can change as the wort becomes more dense. Check this thread out. I think hydrometers need to be used to check the accuracy of your refractometer, not the other way round.

Double check on the paper insert on the hydrometer for the calibration temp. I know most say 60º but oddly enough I have one that says 68º. Go figure.

pcollins said:

Double check on the paper insert on the hydrometer for the calibration temp. I know most say 60º but oddly enough I have one that says 68º. Go figure.

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I'm not an expert and don't want to come off like I think I am but every hydrometer temp adjustment chart I've seen starts at 60. If you calibrate at 68 you're already supposed to be adding .0009, but you're hoping it reads 0? That could get confusing real quick if you ask me.

dbrewski said:

I'm not an expert and don't want to come off like I think I am but every hydrometer temp adjustment chart I've seen starts at 60. If you calibrate at 68 you're already supposed to be adding .0009, but you're hoping it reads 0? That could get confusing real quick if you ask me.

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Yes, it sure does. But some hydrometers ARE calibrated at 68 degrees. I think it's because it's closest to "room temperature" and most people would have to cool even a finished beer sample to read it at 60 degrees. If your hydrometer is calibrated at 68 degrees, it's certainly more convenient as many times a beer sitting after fermentation is right around 68 degrees.

mb2696 said:

I did misspeak by saying that since it's linear it's just an offset.

However, for the reasons zeg pointed out, just because "the error can become greater as the gravity increases" does not mean it is not linear. It could simply be that the glass is the wrong diameter in which case the correction would be a scaling AND offset, which is still linear.

In your experiment I would agree that it looks like the correction for hydro 2 it not simply an offset. However, this does not mean that a hydro should be thrown out if it doesn't read 1.000 in water. You need a second high-ish gravity verification solution (like what you've done). On the other hand, it's $5 for a new one, so maybe it's not worth the time?

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Yea, you're right. That might still be a linear error. I stand corrected. In fact, I can't think of a way that it wouldn't be linear.

This is a good place for the accuracy vs. precision debate. A hydrometer doesn't have to be accurate, but it does have to be precise. The two main uses of a hydrometer are to determine ABV and to be sure your fermentation is complete. The difference between your OG and FG will give you your alcohol content and the same reading over a few days will tell you fermentation has stopped. Neither one requires accuracy.

Yooper said:

Yes, it sure does. But some hydrometers ARE calibrated at 68 degrees. I think it's because it's closest to "room temperature" and most people would have to cool even a finished beer sample to read it at 60 degrees. If your hydrometer is calibrated at 68 degrees, it's certainly more convenient as many times a beer sitting after fermentation is right around 68 degrees.

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It would be convenient, but then you would need a custom temp adjustment scale for anything above 68, correct? You couldn't use a standard table.

AnOldUR said:

This is a good place for the accuracy vs. precision debate. A hydrometer doesn't have to be accurate, but it does have to be precise. The two main uses of a hydrometer are to determine ABV and to be sure your fermentation is complete. The difference between your OG and FG will give you your alcohol content and the same reading over a few days will tell you fermentation has stopped. Neither one requires accuracy.

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Hmmm. So, which is more important for "perfecting" the beer: accuracy in ABV or in FG?

(if there's an offset in the hydro, the ABV calcs will still come out correct, but NOT the FG)

dbrewski said:

It would be convenient, but then you would need a custom temp adjustment scale for anything above 68, correct? You couldn't use a standard table.

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Maybe! But I've never had a finished beer at above 70 degrees before packaging, so no adjustment is needed.

Yooper said:

Maybe! But I've never had a finished beer at above 70 degrees before packaging, so no adjustment is needed.

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Ok but allow me one more question, at 68 does it read zero or does it read .001 (going back to my "confusing to calibrate theme)?

passedpawn said:

Hmmm. So, which is more important for "perfecting" the beer: accuracy in ABV or in FG?

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Let's say your beer finishes at 1.020 on your hydrometer, but it's not accurate and your beer is actually 1.010. If the beer is "perfect" from then on your goal should be an FG of 1.020. Accuracy means nothing to making great beer. It's repeatability (precision) that matters.


Now, communicating your process to someone else is another story. :cross:

AnOldUR said:

Let's say your beer finishes at 1.020 on your hydrometer, but it's not accurate and your beer is actually 1.010. If the beer is "perfect" from then on your goal should be an FG of 1.020. Accuracy means nothing to making great beer. It's repeatability (precision) that matters.


Now, communicating your process to someone else is another story. :cross:

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Right. If you repeatedly make a beer, changing the recipe to suit your tastes, errors will go away.

But if you attempt to match a known recipe, you'll think you've messed up. In fact, the Hydro #2 from the data above was my "go to" hydrometer for 2 years. I thought a lot about how that bend in reality affected my brewing over that period.

dbrewski said:

Ok but allow me one more question, at 68 does it read zero or does it read .001 (going back to my "confusing to calibrate theme)?

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It reads 1.000.

dbrewski said:

I'm not an expert and don't want to come off like I think I am but every hydrometer temp adjustment chart I've seen starts at 60. If you calibrate at 68 you're already supposed to be adding .0009, but you're hoping it reads 0? That could get confusing real quick if you ask me.

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I'm not an expert either so I'll leave it to those who are. This is what it says on the inside of my hydrometer (my bad, it doesn't say "68ºF" LOL ).

In a book that I read, it was stated that most hydrometers are calibrated at 68°F, but to watch out for the occasional 60°F-calibrated models. (I'm not certain, but I *think* it was Schramm's Compleat Meadmaker.) I've been curious whether that was dated info, depended on region, or what, since the only hydrometers I've seen are 60°F models.

I see. It's calibrated at 20 C = 68 F. Sure it says it's calibrated at 68. Just in a different language

Mine states it is calibrated at 60F. Brewing today and just going with the hydrometer in question and hoping for the best since I haven't had a chance to get a new one.

Trying to replicate a recipe which will be tough if I can't rely on the hydro, but hopefully I'll come close

If you own a 68F calibrated unit, do you use a temp conversion chart and if so which one?

Hydrometers such as the one you see here are much more accurate: http://morewinemaking.com/view_product/18653/103323/Hydrometer_-_Brix_0_-_12_With_Correction_Scale - far more accurate than a refractometer. The problem with triple-scale hydrometers is two fold:

1) The range is too wide which means less accuracy
2) There's no built-in temperature correction

That's why a hydrometer like the one above is better. Ideally you'd have two or three depending on your range. The problem is the better ones only come in brix - so you have to get used to that scale. But - brix pretty much equals plato which is pretty much percent sugar content so it makes a lot more sense.

jcaudill said:

The problem is the better ones only come in brix - so you have to get used to that scale. But - brix pretty much equals plato which is pretty much percent sugar content so it makes a lot more sense.

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I'm not sure that statement is accurate, brix and SG measure different things and the conversion is not 100% consistent. I'm on my phone and can't get the url of this thread, but user ajf says it well:

ajf said:

The brix scale is a measure of the amount of sucrose in a solution. Wort contains very little sucrose, but relatively large amounts of maltose and maltotriose. The conversion from brix to S.G. is different for a wine must (almost 100% sucrose) and beer wort (mainly maltose and maltotriose). Because of this, it is not possible to have a S.G. scale on the refractometer that is accurate for both beers and wines. Most refractometers with a dual scale have an S.G. scale calibrated for wine, but there may be some where the S.G. scale is calibrated for beer. Even if you have one that is calibrated for beer, the calibration will change slightly, depending on what went into the wort.

-a.

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[Edit] it is the same link I reference earlier on this thread.

I'm not sure I understand. I didn't mean to imply you should try to convert back to SG because you're right - it does not convert well. What I was trying to say is you're going to have to use Brix (or Plato) going forward for all measurements. But my opinion is Plato makes more sense and it is the standard measurement in most commercial breweries.

I think what he is saying is that the brix scale itself is for measuring something different than plato/SG. So while I wholeheartedly support precision hydrometers (I broke mine last night ) I would recommend getting it in plato or SG, not brix, because of the conversion issue.

the brewer's edge precision hydro from Williams Brewing has twice the resolution of a standard hydro and is reasonably priced. And fragile unfortunately.

If that's the case then no - Brix and Plato both measure % sucrose by weight and are interchangeable.

1 deg Plato = 1% sucrose by weight of a water-sucrose solution = 1% Brix.

Brewer's tend to express measurements in Plato, Vintner's tend to express measurements in Brix.

jcaudill said:

If that's the case then no - Brix and Plato both measure % sucrose by weight and are interchangeable.

1 deg Plato = 1% sucrose by weight of a water-sucrose solution = 1% Brix.

Brewer's tend to express measurements in Plato, Vintner's tend to express measurements in Brix.

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I stand corrected. And confused. I just wonder why homebrewers needed their own scale (SG).

dbrewski said:

I stand corrected. And confused. I just wonder why homebrewers needed their own scale (SG).

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Because we're all science and engineering majors, and SG is what we would have come across in our chem lab classes.

Brix and Plato are just industry-specific measures of SG applied to specific dissolved solids affecting the bulk density of a solution.