Hydrometer Accuracy

[K5MOW]

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?

Well I am checking my hydrometer in distilled water. What should it read? I think it should read 1.000.

Roger

 

[weagle05]

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.

The reduction in density is what you're measuring, so it is not an inaccuracy.

 

[RCCOLA]

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

I got a catalog from Williams brewing and noticed that these appeared to be very nice hydrometers. I didn't know that a bottling hydrometer (1.000-1.040) even existed until seeing it in the catalog.

http://www.williamsbrewing.com/HYDR...serID=3822873&jsessionid=d830652c810b426f4b3f

 

[Aerolithe]

The reduction in density is what you're measuring, so it is not an inaccuracy.

You want to measure the reduction in density that is caused by sugar 'disappearing' through fermentation, but a lot of calculations seem to treat the change in density as sugar disappearing without accounting for the fact that it is actually becoming alcohol, which is less dense than water. For example, the calculations would be exactly accurate if the yeast were fermenting sugar in a 100% alcohol solution, or if the yeast were converting sugar to water. Apparently, commercial breweries measure a specific amount of sample, boil off the alcohol (along with some water), and top it off with distilled water to the original volume. Taking a specific gravity reading of this alcohol-free sample would let you calculate exactly how much sugar was lost, and this could be used to determine how much alcohol was added.

 

[Frodo]

Well I am checking my hydrometer in distilled water. What should it read? I think it should read 1.000.

Roger

Roger Roger... Sorry I just had to... bet you've never heard that one before! 1.000 at calibration temp which should be stated on the hydrometer; it's usually 60F.

 

[K5MOW]

Roger Roger... Sorry I just had to... bet you've never heard that one before! 1.000 at calibration temp which should be stated on the hydrometer; it's usually 60F.

Well I was pretty sure that it was 1.000 but I just wanted to be sure. Mine is right on. Thanks so much.

Roger

 

[Frodo]

You want to measure the reduction in density that is caused by sugar 'disappearing' through fermentation, but a lot of calculations seem to treat the change in density as sugar disappearing without accounting for the fact that it is actually becoming alcohol, which is less dense than water. For example, the calculations would be exactly accurate if the yeast were fermenting sugar in a 100% alcohol solution, or if the yeast were converting sugar to water. Apparently, commercial breweries measure a specific amount of sample, boil off the alcohol (along with some water), and top it off with distilled water to the original volume. Taking a specific gravity reading of this alcohol-free sample would let you calculate exactly how much sugar was lost, and this could be used to determine how much alcohol was added.

That sounds... complicated... it really doesn't need to be.

The specific gravity is the specific gravity; that's a fact; a hydrometer measures the specific gravity; that's another fact. No need to make that complicated.

Alcohol being less dense than water if added to water would make the specific gravity less than 1.000. When a beer is done fermenting, it has residual sugars in it, along with alcohol. The specific gravity when it's done fermenting is called the final gravity or FG. That specific gravity can be measured directly with a hydrometer, since a hydrometer measures specific gravity. If you took out all of the alcohol from the beer, the specific gravity would then be higher. Ok I'm done beating the horse.

 

[Frodo]

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?

Alcohol isn't dissolved into beer, it's just another liquid portion of the beer; something being dissolved into a liquid implies that it was once a solid (or could be precipitated out of the solution). I imagine it would take some crazy cold temp to freeze alcohol into a solid. A refractometer reading after fermentation has started is skewed by the alcohol; it can be reasonably corrected though as long as you know the OG. There is a refractometer tool in BeerSmith (and I believe there are calculators online, and in the other software as well) to do this.

 

[MalFet]

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.

Check out Fisher Scientific. They have a 150mm 1.000-1.070 hydrometer that would be reasonably good all-purpose. For more precision you'd typically want to get a few of them specifically targeted to particular ranges, but that's probably overkill for our purposes.

Regarding the refractometer:

As other people have mentioned, you can figure out your corrected FG if you know your OG. MoreBeer's spreadsheet is popular. Some people have reported that these calculations are relatively inaccurate, but I've always found them to be pretty darn good. One problem, though, is that you get compounding errors. If you're off in your first reading by a point or two and then off in your second reading by a point or two, your final reading can be off quite significantly.

 

[weagle05]

You want to measure the reduction in density that is caused by sugar 'disappearing' through fermentation, but a lot of calculations seem to treat the change in density as sugar disappearing without accounting for the fact that it is actually becoming alcohol, which is less dense than water. For example, the calculations would be exactly accurate if the yeast were fermenting sugar in a 100% alcohol solution, or if the yeast were converting sugar to water. Apparently, commercial breweries measure a specific amount of sample, boil off the alcohol (along with some water), and top it off with distilled water to the original volume. Taking a specific gravity reading of this alcohol-free sample would let you calculate exactly how much sugar was lost, and this could be used to determine how much alcohol was added.

I was obviously simplifying things a bit, but thank you. I didn't realize breweries would do all that, however it makes sense with the regulatory hurdles they have to deal with.