measuring sg with a scale

[native_sun]

Just wondering if anyone measures their sg with a scale rather than a hydrometer. I remember doing this back in school, and a little digging got me the formula. I don't own a hydrometer, but I do own a few nice acurrate scales(digital reloading scales, but they do measure in grams as well as grains) and a graduated container. I've never been terribly concerned with my final abv, all my stuff has been strong enough for my liking, but I'm thinking it couldn't be bad to know on whatever I make in the future. Does anybody else use this method rather than a hydrometer?

 

[WI_Wino]

Nope, a hydrometer is just so easy.

 

[AZCoolerBrewer]

I thought about this for a good long time. This method would not work if you had trub floating around in your wort as the trub adds irrelevant weight with unknowable volume. You could however make a quick correction to your formula by using a hydrometer.

 

[flars]

There is a topic on the same subject that ended a week or two ago. Just seems like to much of a hassle with all the variables especially getting the exact volume of beer each time.

 

[feinbera]

Your biggest problem is going to be accuracy. Volumetric measurements kinda suck, being a couple percent off is hard to avoid, even with good graduated glassware, but, a couple percent is the different between 1.045 and 1.065. Maybe being within a few points is "good enough" for OG, but no way you'll be able to tell when your FG has stabilized.

 

[Rhumbline]

Yeah, I started a thread a while back where I was looking into this. The main difficulty came from not being able to accurately measure volume. I think even being off by one fluid ounce was enough to throw the calculation.

I did find that it was ok for determining when fermentation had stopped, with the weight remaining the same for a few days running.

 

[native_sun]

Not being snotty about it, but how is getting an exact volume measurement in a graduated cylinder any more difficult than getting an exact reading on a hydrometer? To my knowledge, the same issues apply to both, with the added issue of the fact that a hydrometer can move up and down in the liquid if the container or table gets bumped. IIRC, that is why most chemistry textbooks recommend weighing as more accurate. As long as you use the same volume every time( the exact measurement is irellivant), you should be golden. The only real advantage I can think of is that hydrometers are graduated in specific gravity, which takes the math out, so using one would be easier, I admit. The particulate issue could be a problem, but there are ways around that as well.
Addendum: a quick google search tells me that the weighing method is the method used to calibrate hydrometers.

 

[Oginme]

To measure specific gravity by using weight/volume, you first need an extremely accurate scale capable of measuring at least to the thousandths of a gram. Next you will need a volumetric pipet to make sure the volume of the wort/beer is accurate. Small errors will start to add up.

There are specific gravity cups which are commonly used for high gravity paints and coating fluids. They will run you several hundred dollars and the accuracy is only good to about the hundredths level.

In both of these cases, the temperature of sample and containers must be consistent at 20C to ensure any reliability.

Using a hydrometer is a matter of a measuring tube (which could be a graduated cylinder) and the hydrometer. Exact volume is unimportant as long as the hydrometer floats freely. It takes approximately 2 to 3 minutes to do the whole procedure. Small changes in readings due to temperature can be easily and reliably converted to standard conditions. The stability of the hydrometer in solution is a matter of less than 1 minute unless the surface you use for placing the graduate is unstable. If this is the case, then your scale would be just as susceptible to the vibrations and give you errors.

As someone who has worked in coatings, paints, and ink technology for 30+ years, we used hydrometers and refractometers as a standard method of measuring density, sugar, and starch concentrations. Much easier, faster, and more economical than a laboratory scale.

 

[Rhumbline]

Not being snotty about it, ...

I didn't think you were being snotty, you just didn't seem to understand the issue.

The problem is that you need to very accurately measure the volume of about 5.5 gallons of liquid, you are not measuring the volume of a 4 oz sample.

I'll let you do your own math but being off by just one fluid ounce will cause an error of .0138 points in your SG. With the fermenters I use, that level of accuracy isn't attainable.

 

[native_sun]

I didn't think you were being snotty, you just didn't seem to understand the issue.

The problem is that you need to very accurately measure the volume of about 5.5 gallons of liquid, you are not measuring the volume of a 4 oz sample.

I'll let you do your own math but being off by just one fluid ounce will cause an error of .0138 points in your SG. With the fermenters I use, that level of accuracy isn't attainable.

Why would I have to measure the full amount of liquid rather than a sample. I don't grasp the logic there. Also, ml is a much more sensible unit than oz. My sample size couldn't possibly be off by an ounce if my sample size is less than an oz and measured in ml ( roughly 29.6 ml to a fluid oz)

 

[signpost]

Why would I have to measure the full amount of liquid rather than a sample. I don't grasp the logic there. Also, ml is a much more sensible unit than oz. My sample size couldn't possibly be off by an ounce if my sample size is less than an oz and measured in ml ( roughly 29.6 ml to a fluid oz)

As I read the thread, I wondered the same thing. It seems that if you already have equipment that is accurate enough to satisfy your needs, then go for it. If you find it doesn't give consistent/accurate results, then you might consider going for a hydrometer, as they aren't that expensive. But if you'd rather use things you already have instead of spending extra money to do it "the right way," then I would say go for it.

 

[Rhumbline]

Why would I have to measure the full amount of liquid rather than a sample. I don't grasp the logic there. Also, ml is a much more sensible unit than oz. My sample size couldn't possibly be off by an ounce if my sample size is less than an oz and measured in ml ( roughly 29.6 ml to a fluid oz)

Ok, I see where the disconnect is. My reason for wanting to try to calculate SG by weight is that I was curious if there was a way to determine SG without opening the fermenter and potentially introducing some contaminant.

Your method doesn't offer a way to accomplish my goals. You are correct in that it should be entirely possible to do this with a small sample size.

But a small sample size demands even more accuracy in measuring volume and weight.

20 milliliters of water weighs 1.25027 grams.
Each .001 point in SG will add .00125 grams to the sample.

and the above does not take into consideration temperature corrections or other factors affecting the measurements.

So, if you have the ability to measure weights to 1/10,000th of a gram and volume to a like accuracy then your method would work. However, it does not achieve my goal of simplifying the process.

 

[Oginme]

Ok, I see where the disconnect is. My reason for wanting to try to calculate SG by weight is that I was curious if there was a way to determine SG without opening the fermenter and potentially introducing some contaminant.

Your method doesn't offer a way to accomplish my goals. You are correct in that it should be entirely possible to do this with a small sample size.

But a small sample size demands even more accuracy in measuring volume and weight.

20 milliliters of water weighs 1.25027 grams.
Each .001 point in SG will add .00125 grams to the sample.

and the above does not take into consideration temperature corrections or other factors affecting the measurements.

So, if you have the ability to measure weights to 1/10,000th of a gram and volume to a like accuracy then your method would work. However, it does not achieve my goal of simplifying the process.

Not to discount your argument, which is fairly valid as far as accuracy is concerned, but 1 ml of water = 1 cc of water at 20C = 0.9982 grams. 20 ml of water would be 20 ml * 0.9982 g/ml = 19.964 grams.

Each point increase in sg would be: 0.9992 g/ml * 20 ml - 19.964 g = .02 grams (once again at 20C).

The point is: can it be done by weight of a known volume -- yes. Are there much easier ways which are just as accurate -- yes.

 

[Rhumbline]

Not to discount your argument, which is fairly valid as far as accuracy is concerned, ...

The point is: can it be done by weight of a known volume -- yes. Are there much easier ways which are just as accurate -- yes.

Thanks, I'm an imperial units kind of guy and I should have known better to try all those conversions, bound to introduce some errors.