Hydrometer Accuracy

I broke my hydrometer yesterday so I went out and bought a new one today. I tested it out in distilled water (purchased from the store) at room temperature (68 degrees, verified with my thermometer).

The hydrometer read 1.004, with temperature compensation, thats nearly 1.005. Is it normal for hydrometers to be off by this much? Should I return it?

Sadly, that's pretty typical. Return it if you can. I had a hydrometer from a major homebrew shop off by 7 points not too long ago.

Some are calibrated at 60*F....

It should say on the label...

I'm positive it's on the sheet that came with my hydrometer but since I'm not at home right now, what is the equation for the temperature conversion?

Never mind.....it's called GOOGLE SEARCH!

It depends on the model of hydrometer, but typically if you have a 60F hydrometer and you take a reading at 68F, you need to add .001 to your reading to get an accurate gravity.

gio said:

I broke my hydrometer yesterday so I went out and bought a new one today. I tested it out in distilled water (purchased from the store) at room temperature (68 degrees, verified with my thermometer).

The hydrometer read 1.004, with temperature compensation, thats nearly 1.005. Is it normal for hydrometers to be off by this much? Should I return it?

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My opinion is that you don't really need a hydrometer that is accurate to three decimal places.

broadbill said:

My opinion is that you don't really need a hydrometer that is accurate to three decimal places.

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That's sorta how I feel.

Mine is off by 4, I just take all my readings and minus 4!

Also if you measure really hot wort or drop the hydrometer just the right way, the glue that holds the paper in place can release and you'll be screwed. We had a guy in the LHBS with a hydrometer that read 1.020 in distilled water. He had dropped it and the paper slid.

broadbill said:

My opinion is that you don't really need a hydrometer that is accurate to three decimal places.

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Completely disagree.

If you want to be able to hone in your craft and your brews, an accurate hydrometer reading is essential. If you are doing an all grain batch, for example, a pre-boil SG of 1.057 vs 1.052 could mean an efficiency of 75% vs 68%.

I would return it and get one that is properly calibrated.

Standard practice in science would be to read the hydrometer to one decimal place beyond what it shows. For example, if your hydrometer is marked at 1.05 and then again at 1.06, there is enough space for you to be able to easily determine where 1.055 is, and by extension to be able to reasonably estimate to the thousandth place.

Bmorebrew said:

Standard practice in science would be to read the hydrometer to one decimal place beyond what it shows. For example, if your hydrometer is marked at 1.05 and then again at 1.06, there is enough space for you to be able to easily determine where 1.055 is, and by extension to be able to reasonably estimate to the thousandth place.

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With the hydrometer with a standard 0.002 mark divisions, I tend to only estimate to 0.001 and no further. This is purely due to the fact that the marks are rather close, it can be hard t estimate with the way the fluid shapes and moves around the hydrometer, and there is no real need to go beyond that 0.001 accuracy in home brewing.

This is what I do too. By the time you would factor in compounded error, 0.002 is plenty sufficient.

No reason not to have an accurate hydrometer. If you get one that does not calibrate send it back.

One thing I have found is that's it's easier to get a good reading out of a nice glass test tube. (As compared to the cheapo plastic ones) Keep it clean with no sticky residue on the inside. As you take the reading wipe the tube down with an anti-static drier sheet. It also does not hurt to put a drop of food coloring in the tube with light beers so you can see your wort/beer easier.

I'm sure some lab geek will punch holes in all that I just said, but this is what I do when I want a real accurate reading. My eyesight is not all that great and in the past I struggled to get a consistent reading, but nice clean glass tube, bit of color, static removed, makes me confident of my readings.

I would check it again at 59 degrees. I got a new one after breaking one and i thought it read.986 if that makes sense. I Then check it at 58 -9 degrees and it was at 1.00. Almost was going to take it back.

I took the reading at 68 degrees and it was 1.004. At 60 degrees (which it is supposed to be calibrated for), it would read even HIGHER. Which is why I say that adjusted it read 1.005. That's quite a large amount to be off by. It's supposed to be +/- .002 accuracy. I'm definitely taking it back.

broadbill said:

My opinion is that you don't really need a hydrometer that is accurate to three decimal places.

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I think you must be kidding... OP no reason not to return it; screw "adding" 5 pts every time to compensate, cause guaranteed you'll end up taking a reading, write it down, then wonder later whether you remembered to add. You paid for a scientific instrument, it should be accurate.

Frodo said:

I think you must be kidding... OP no reason not to return it; screw "adding" 5 pts every time to compensate, cause guaranteed you'll end up taking a reading, write it down, then wonder later whether you remembered to add. You paid for a scientific instrument, it should be accurate.

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First off, Its not a scientific instrument. THESE are scientific instruments:

http://www.coleparmer.com/catalog/product_index.asp?cls=2413

they start at $40 and go up from there...a little bit different from the $8 version at your LHBS!

Secondly, if you find adding 5 points to a hydrometer reading too mentally taxing, maybe home-brewing isn't for you.

Frodo said:

I think you must be kidding... OP no reason not to return it; screw "adding" 5 pts every time to compensate, cause guaranteed you'll end up taking a reading, write it down, then wonder later whether you remembered to add. You paid for a scientific instrument, it should be accurate.

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broadbill said:

First off, Its not a scientific instrument. THESE are scientific instruments:

http://www.coleparmer.com/catalog/product_index.asp?cls=2413

they start at $40 and go up from there...a little bit different from the $8 version at your LHBS!

Secondly, if you find adding 5 points to a hydrometer reading too mentally taxing, maybe home-brewing isn't for you.

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Don't make me turn this car around, you two!

Before this thread comes to blows...the OP's question has been answered: It is not that uncommon for cheap homebrew hydrometers to be off by even significant amounts. You can calibrate a hydrometer by testing it in distilled water (and, ideally, again in a solution of known gravity). Whether it's easier to keep the hydrometer and subtract five or to return it and get a (hopefully) better one is something only the OP can answer for himself.

okay i am not sure i see what the issue is here. bear in mind i am new to brewing, but it would seem to me that if it is off by .002 or by .05 it doesn't really matter. (OG + .002) - (FG + .002) is still going to give you your actual reading ... the difference cancels out. i understand if you pay for something you expect it to be right, but i also understand you get what you pay for. as another stated these aren't scientific instruments, not at those prices. ;j


not trying to stir the pot, just looking for what i am missing here.

edsrockin said:

okay i am not sure i see what the issue is here. bear in mind i am new to brewing, but it would seem to me that if it is off by .002 or by .05 it doesn't really matter. (OG + .002) - (FG + .002) is still going to give you your actual reading ... the difference cancels out. i understand if you pay for something you expect it to be right, but i also understand you get what you pay for. as another stated these aren't scientific instruments, not at those prices. ;j


not trying to stir the pot, just looking for what i am missing here.

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That will give you a precise _change_ in gravity, but there is plenty of reason that someone would want to know the gravities themselves. OG 1.030 -> FG 1.000 is very different than OG 1.050 -> FG 1.020, no?

broadbill said:

First off, Its not a scientific instrument. THESE are scientific instruments:

http://www.coleparmer.com/catalog/product_index.asp?cls=2413

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Forgive me... I was under the impression that any instrument that measures a quantifiable value is considered a scientific instrument, and that there are highly accurate and precise scientific instruments (which you seem to be calling "scientific instuments" and which cost a lot more), and less accurate and precise scientific instruments (which is what you can buy in the LHBS).

EDIT: my point was that if the accuracy of the hydrometer the OP bought is supposed to be within 2 pts, and it is 5 pts off, then it does not meet the stated accuracy and therefore is a defective "instrument" (I don't want to imply it's in any way whatsoever that it's actually a "scientific instrument", as use of that term seems to really bug you).

okay malfet, your point is taken, but not trying to be an arse as much as try to understand it. remember i am new to the game. ;j


why would you need just an OG or just an FG? without one what good is the other i guess is what i am driving at? thanks.

you can get very accurate hydrometers

they aren't terribly expensive.

edsrockin said:

okay malfet, your point is taken, but not trying to be an arse as much as try to understand it. remember i am new to the game. ;j


why would you need just an OG or just an FG? without one what good is the other i guess is what i am driving at? thanks.

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Sure thing, and I didn't mean to come of as snarky either. OG is very important, because it tells you how much dissolved sugar your wort contains. This is important for recipe design because a very large OG will produce a very different beer than a very small one. Think of the difference between a barley wine and a brown ale...roughly equivalent ingredients, but in wildly different quantities.

In production, OG can be very important too. This is less of an issue in extract brewing, just because it's much harder to screw up your gravity. If your recipe is designed properly and you use the right amount of the right ingredients in the right quantity of water, you're pretty much guaranteed to hit your target gravity. In all grain brewing, however, there are many other factors that can influence how much of the sugars you are able to extract from your malts.

As for FG, the percent attenuation is usually more important than the absolute gravity drop. A beer that goes from 1.040 to 1.010 is probably done fermenting, as it represents a 75% apparent attenuation ((40 - 10) / 40). A beer that starts at 1.090 and only drops to 1.060, however, is only attenuating 33% and is likely a heck of a long way from done. This despite the fact that they both dropped exactly 30 points. So your final gravity will be different for different styles of beer, and your amount of gravity change will be different for different kinds of yeasts.

When you're just starting out, the main purpose of gravity is as a diagnostic. If you start out too low or end up too high, that's important to know so you can figure out if there is a problem. As you get more familiar, understanding gravity becomes important to designing recipes. A good saison, for instance, should end up very dry...say 1.010. A malty scottish, on the other hand, is probably better higher.

Hope this helps

it did indeed! thanks for putting in noob terms.

i didn't think you were snarky btw, i just didn't want you to think i was being so. this electronic comm. is pretty lame for expressing how you mean what you type sometimes. i try to err on the side of caution.

again, thanks.

OG is actually very important because I use it to calculate my efficiency and modify my mash methods. If I hadn't tested my new hydrometer, I would have thought my efficiency had suddenly gone up by 5% or more and I would be wondering what I was doing differently.

Also, I live only about a block from my LHBS so it's not too much of a trouble to exchange it.

I seem to break hydrometers regularly. Tile floors and glass don't mix well.

My newest is off by .002 and it drives me crazy. I simply adjust my readings, based on a reading I took with water at 60 F.

The problem with returning it for a new one is that the new one may be off as well.

I chased this problem for 2 years and finally checked/verified the meter in h2o. The paper inside the glass tube was moving! (I made a painfull assumption that this wasn't possible) Try tapping on a kitchen towel while observing the scale's position.

I agree with Tall Yotie. and from my own dumb arse experience , If you decide to get a thermo-hydrometer, do not drop it in wort that is over like 170% or you could screw up the thermometer part.

check that...the high temp mark on my thermo-hydrometer is 120.

Given the etreem accuracy of home brewing...

motobrewer said:

you can get very accurate hydrometers

they aren't terribly expensive.

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whats considered an appropriate amount of money to spend on a quality hydrometer.. in other words, is it worth buying a nice hi/low hydrometer set or is the basic one good enough.

Ten-Seven said:

Given the etreem accuracy of home brewing...

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Speak for yourself

Ten-Seven said:

Given the etreem accuracy of home brewing...

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MalFet said:

Speak for yourself

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RIGHT!?!?!?

havent you seen yuri's steam mashing setup, with the digital temp probe and custom computer board... tell me hes not accurate.

Im actually thinking that homebrewing is more precise than commercial brewing, just because of the scale... I betcha there is more "wiggle room" at the big breweries.

Just to keep this going, but a bit different angle...

Calibration at a single point (distilled water) is not a great calibration in general. In my line of work we calibrate many different instruments, nearly all of them use at least 3 points to check accuracy across a wider range.

Specific to the assumed problem of the paper slipping down over time, it seems that making an adjustment a few points would work. But I have a hydro that reads 1.004 in distilled water, but when tested with 2 different solutions (1.020 and 1.050) of table sugar weighed out into measured volumes of water it reads fine. 1.020 is way closer to most of my FG's than 1.000, so I'm rolling with this hydro as is, not correcting for the 1.004 reading.

Do with that what you will...

Keep in mind that it won't necessarily be off by just a constant. The spacing between marks may not be accurate, either, especially if it isn't in the correct position to begin with (if 1.000 isn't in the right spot), so that it reads 1.005 when its in distilled water, but in a wort that is actually 1.050 it reads 1.062, or it reads 1.050 but because it was wrong at 1.000 you still add .005 to compensate. As was mentioned above, the only way to be truly sure of your hydrometer is to do a test with distilled water at 60 degrees, then mix up a batch of sugar (sucrose?) and distilled water, figure out its theoretical specific gravity, and see what the hydrometer says. Using this, you could correctly scale your hydrometer, but thats a lot more math that just adding/subtracting, and I'd feel more comfortable just starting with a precise instrument from a reputable scientific instrument manufacturer. Personally, I think I'll shell out for the $40 name brand model sooner or later.

Edit: Whoops, missed like two pages of discussion, looks like this has already been covered

I returned it and got another one. The LHBS tested it themselves and indeed it was off by 0.006 for them so they agreed I should try a new one.

The new one is off by 0.003 (reads 1.003 in distilled water. I'm a little happier with it but its still not ideal. I'm beginning to think the brand of hydrometer they sell just isn't very good. My original hydrometer that came with my brewing kit was spot on 1.000 in distilled water.

Can anyone recommend a good hydrometer? I don't mind paying a little more for the accuracy.

gio said:

I returned it and got another one. The LHBS tested it themselves and indeed it was off by 0.006 for them so they agreed I should try a new one.

The new one is off by 0.003 (reads 1.003 in distilled water. I'm a little happier with it but its still not ideal. I'm beginning to think the brand of hydrometer they sell just isn't very good. My original hydrometer that came with my brewing kit was spot on 1.000 in distilled water.

Can anyone recommend a good hydrometer? I don't mind paying a little more for the accuracy.

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Get a refractometer?

In any case, is it not true that due to it's lower density, alcohol dissolved in fermented beer causes an inaccuracy of the FG reading. Clearly I do not understand the details of this but would appreciate the input of one who does. Also, doesn't a refractometer require some form of conversion when it comes to interpreting FG?

jonmohno said:

Get a refractometer?

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I thought a refractometer is only good before fermentation. Something with the alcohol?