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Hydrometer questions

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AsharaLyn

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Jul 21, 2007
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asharalyn.twisted-reality.com
I was wondering about the accuracy of my hydrometer, so I filled up the tester with water. After leaving it for an hour or more so that the aeration could settle out (we have a filtration system), the reading was 0.994, which is pretty far from 1.0. I know that temperature can affect the SG reading, but what about elevation? It seems that the gas law has both pressure and temperature in it, as well as volume (which doesn't affect liquids nearly as much as gases). Come to think of it, pressure has a lesser effect on liquids than it does on gases, too.

Also, the hydrometer is a sealed glass tube with a printed paper in it. This seems very low tech as a measurement apparatus. Are these the way to go, or is there a better method?

And finally, in a pure grammar geek kind of way, I note that I used both affect and effect properly in the same post. :laughing7:
 
Hi Sarah,

My hydrometer reads .002 on the low side in distilled water. It's consistent though so I just take that in to account when I take my readings. I've compared it to other hydrometers at different SG's and it's always about .002 points low.

Since a hydrometer is measuring the density of the liquid, rather than a volume, pressure or other measure, altitude should have little or no affect.

Also, did you use distilled or tap water when you checked the calibration? it won't make much difference but there will be some if you have a high mineral content.

Some people use a refractometer in place of a hydrometer. They are very accurate for getting your OG but you need to run your readings through a complex formula to measure SG after fermentation begins. The alcohol content throws it's readings off. If you own a program like ProMash, there are refractometer calculators built in. I've also seen spreadsheets that will do the math for you. One nice feature of the refractometer though is that it's pretty much temperature independent. I believe Oskaar uses one.

Cheap as I am, I'll stick with my known $5.00 hydrometer vs. a $40.00 refractometer!
 
you must have been at this for a long time becuas there about 12$ now at least thats what I payed for mine
:happy10:
 
Glad to hear they haven't gone up too much lumberjack. But 3 in a year? Damn! I hate to say it but ... Stop eating butter when you ferment!

Maybe I should put mine up on e-bay as an ancient artifact! Hell, there was a bottle of beer that from 1852 that recently sold for $503k. That relates to $324.52 per year since the initial purchase. I'm looking at $0.38 per year since I bought my hydrometer. You are looking at $21.00 per year. Way more than me but still less than that bottle of beer!

(ain't numbers fun? there are lies, damn lies and then there are statistics)
 
We do have very hard water, but as I said, it was filtered. If anything, hard water with lots of minerals would register as more dense than distilled water. As for pressure, at higher elevations, the air pressure is lower. The air doesn't push down on the water as much, making it less dense. I was wondering if someone here had already done the calculations to find out if there was a correction, or if it was even enough to worry about. The temperature adjustment was posted somewhere else earlier, but since my sample this morning was pretty close to room temp I wasn't so interested in it. Maybe I should pick up some distilled water tomorrow and test it for myself :).
 
PV=NRT. Boyle said it best. That's not only a good idea, it's the law, kinda like the speed of light. There is no where in that equation to accommodate elevation (sure, you could argue the "P" side of things for pressure but liquids are so much less compressible than gasses that it's not a factor.

We are still talking the amount of suspended solids in a liquid (hence, the density of the liquid) and pressure is not going to be a factor here.

And filtering will not necessarily give the same results as pure, distilled water. It depends upon the filtration you have in effect. What is being filtered? And what is left?

Another issue too: you let your initial sample set for quite some time. You will always get a build up of bubbles on your hydrometer if you do that. Did you give things a good swirl to get rid of those bubbles? Bubbles on the sides of your hydrometer will lower your reading. The bubbles will make it float higher.

I'm not trying to bust your chops Sarah. I'm trying to help you eliminate variables that I've encountered before. As low as your hydrometer is reading, as long as you're making temp corrections, either live with it or move on to a refractometer. Like I said, there are experts here who know how to use them. Me? I'm too simple. I know how far off my hydrometer is and I've verified it. That's all I need!
 
wildaho said:
Glad to hear they haven't gone up too much lumberjack. But 3 in a year? Damn! I hate to say it but ... Stop eating butter when you ferment!

Maybe I should put mine up on e-bay as an ancient artifact! Hell, there was a bottle of beer that from 1852 that recently sold for $503k. That relates to $324.52 per year since the initial purchase. I'm looking at $0.38 per year since I bought my hydrometer. You are looking at $21.00 per year. Way more than me but still less than that bottle of beer!

(ain't numbers fun? there are lies, damn lies and then there are statistics)
Click to expand...

All I can say is that you don't even want to know how old my hydrometer is! Too bad they're not vintage dated!! :laughing7:

Regarding the pressure argument -- well, wildaho is right on, because the proportionality between pressure and volume is applicable only to gases, and "ideal" ones at that. Most liquids are usually referred to as "incompressible" fluids because to the first order, they are.
 
AsharaLyn said:
Excellent :). That means that today I need to get ahold of some distilled water and see how far off my hydrometer actually is.
Click to expand...

Yup! In fact I have a complete 2-point calibration chart for my hydrometer that I made myself many years ago. I used distilled water at several different temperatures and took SG measurements, and did the same thing for a known amount of sugar dissolved in a known volume of water (to make a reference 1.100 SG). This way I know just how far off my hydrometer is over the entire range of temperatures that I'm likely to use it. It is amazingly linear and... the distilled water reads 0.999 (just under the 1.000 line) at 70F, and the reference dilution was also just under the 1.100 line at 70F. I guess I got lucky; my paper scale is in exactly the right place in this one - no systematic hydrometer error! Guess they built 'em better 25+ years ago....
 
Probably not Made In China then! Good to hear that it's linear, that means I don't have to do my own range of temp calculations :). I did far too many of those types of experiments back when I was studying Physics in college. I love it when they give you an experiment to replicate and their version *doesn't work*, and your 'real' assignment is to figure out why it's not working, and how to fix it.
 
1: Anyone who has the same hydrometer for 13 years deserves a prize! I am on my 3rd one.

2: I dont know for sure if air pressure effects it but I think it probably would. I am in colorado and mine with tap water reads 0.996. In the town I am in we have high florine and other trace elements. Nothing that I would think would mess up a reading I bring it up because water being 1.000 is in perfect conditions. As another poster put it it will still give accurate readings from start to finish. You just have to adjust where it starts from.
 
Another (related) hydrometer question...

How much (in a numerical sense) can having fruit bits suspended in your must affect the hydrometer reading?

My Apple Pie Cyser is nearing the end of fermentation, and I'm wondering whether my readings are being affected by the apple bits (unfiltered juice) and raisin bits (they disintegrated during fermentation) and spice bits. Or not really whether it's affecting the readings, but by how much. I'm doing the whole cold crash the yeast and particles out (it drops clear in about 12 hours in the fridge) then rack and let the cyser come to room temperature, then remeasure the SG, but I thought I'd ask if anyone had an adjustment figure already.
 
See here for hydromter temperature correction scale. Just look up the temperature your reading was at, and then add/subtract the appropriate correction factor to the SG and, waarlaar (voila) there U are!

Hope that helps,

Oskaar
 
The line that interests me is this:

The fifth methods accounts for 3 degrees Brix (0.021 degrees specific gravity) worth of non-sugar solutes and 51.1% by weight alcohol yield.
Click to expand...

Is this a normal cyser amount? That would mean my 1.04 readings are measuring an SG of 1.02ish, which is more in line with the "sweet but not oversweet" flavor. Is this a meaningless question? (As in, meads/musts vary so much that this is only a good rule of thumb, but not accurate within 0.005, etc)

Also, I like the fact that they give the formula for the temperature adjustment as well as the table. Now I can measure the SG of the sample straight from the fridge and calculate the 'real' SG :).

Thanks, Oskaar!
 
Rhianni said:
1: Anyone who has the same hydrometer for 13 years deserves a prize! I am on my 3rd one.
Click to expand...

So what's my prize? Inquiring minds (including Oskaar who may be eligible for the grand prize ;D ) wish to know. ;D ;D ;D

For the average low cost hydrometer, you can expect readings that aren't quite on. No biggie, you get what you pay for. Myself, I like a fairly accurate reading but that's all I need. I honestly don't care too much if my calculated ABV isn't quite accurate, or my final gravity is a shade off from the actual value. So long as the readings are in the ballpark, I'm happy.

For a few more buck$, you can pick up lab quality hydrometers with finely calculated scales, no problems with the paper scale being out of place, that will give much more accurate readings. Willims Brewing has them, I'm sure other retail sources carry them as well. They're really not all that expensive, well affordable, and they give really excellent results. Still, even though I have a good lab quality hydrometer, I still find myself using the old one, just out of habit.
 
AsharaLyn said:
The line that interests me is this:

The fifth methods accounts for 3 degrees Brix (0.021 degrees specific gravity) worth of non-sugar solutes and 51.1% by weight alcohol yield.
Click to expand...

Is this a normal cyser amount? That would mean my 1.04 readings are measuring an SG of 1.02ish, which is more in line with the "sweet but not oversweet" flavor. Is this a meaningless question? (As in, meads/musts vary so much that this is only a good rule of thumb, but not accurate within 0.005, etc)

Also, I like the fact that they give the formula for the temperature adjustment as well as the table. Now I can measure the SG of the sample straight from the fridge and calculate the 'real' SG :).

Thanks, Oskaar!
Click to expand...

Normal is a moving target from person to person and taste buds to taste buds. Ken has a good set of loose guidlines in his book "The Compleat Meadmaker" (Ken, hope you don't mind me pimping your book every other post! LOL) on page 64 if I remember correctly. If that's not the right page then I'm fully prepared to deny in court that I ever said it was so!

Cheers,

Oskaar
 
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