Hydrometers and Specific Gravity 101

[JoshR 4,697]

We recieve many calls and emails here at Mr. Beer on how to use a hydrometer. Many of the hydrometer instructions can be confusing to newbies so I thought I would create this primer on the correct way to use a hydrometer and the explanation of specific gravity.

Understanding Your Hydrometer:

The hydrometer is a simple instrument that measures the weight (or gravity) of a liquid in relation to the weight of water. Because the relation of the gravity to water is specified (1.000), the resulting measure is called a specific gravity. A hydrometer will float higher in a heavy liquid, such as one with a quantity of sugar dissolved in it, and lower in a light liquid, such as water or alcohol. The average homebrewer has a very keen interest in the amount of sugar dissolved in their wort, for yeast converts sugar into carbon dioxide and alcohol. By knowing how much sugar one started with and ended with, one can easily calculate the resulting alcohol content.

There are many variants of the hydrometer. Some have only one scale, some two and some three. The typical hydrometer measures three things: specific gravity (S.G.), potential alcohol (P.A.), and sugar.

How To Use Your Hydrometer:

It's really pretty easy to use the hydrometer; just follow these simple steps:

1. Sanitize the hydrometer, test jar, and any tools that may come into contact with your wort/beer.

2. Place test cylinder on flat surface.

3. Draw a sample of "clean" wort/beer (Avoid testing samples that contain solid particles, since this will affect the readings.)

4. Fill the test jar with enough liquid to just float the hydrometer - about 80% full.

5. Gently lower the hydrometer into the test jar; spin the hydrometer as you release it, so no bubbles stick to the bottom of the hydrometer (this can also affect readings).

6. Making sure the hydrometer isn't touching the sides of the test jar and is floating freely, take a reading across the bottom of the meniscus (see image below). Meniscus is a fancy word for the curved surface of the liquid.



7. Be sure to take good records of your readings!

That's it! Pretty simple, huh?

There are a couple of other things you need to know to get an accurate measurement.

Most hydrometers are calibrated to give correct readings at 59-60 degrees Fahrenheit. Higher temperatures thin the liquid slightly and result in lower readings than you'd get at the correct temperature. At 70 degrees F., the reading will be 0.001 low. To correct it, add 0.001 to the reading. At 77 degrees F., add 0.002. At 84 degrees F., add 0.003. At 95 degrees F., add 0.005. At temperatures above 95 degrees F., you risk killing your yeast and losing your beer. If you can't remember all that just print out the chart below.



Another thing you need to know is that most hydrometers come with three scales. Specific Gravity, Balling, and Brix are the ones that are usually on your hydrometer. Specific Gravity and Brix are the ones that are most used. Sugar can be measured as ounces per gallon, or as degrees Balling, or Brix. Ounces per gallon are measured on a numeric scale in which an S.G. of 1.046 equals 16 oz. (one pound) of sugar per U.S. gallon. Brix is measured as a percentage of sugar by which pure water has a Brix of 0 (or 0% sugar), an S.G. of 1.046 equals a Brix of 11.5 (11.5% sugar), and an S.G. of 1.095 equals a Brix of 22.5 (22.5% sugar). If you have a choice and want to simplify your life, buy a hydrometer that measures sugar by ounces per gallon.

That should cover everything you need to know about your hydrometer and how to use it. Here are a few tools that may help:

Handy Tools:

Brix/SG Conversion Calculator

Hydrometer Temperature Adjustment Calculator

Cheers!
 

[RickBeer 6,214]

This video is very good also.  And remember, while you only need one tube, you should buy two hydrometers, because they are known to commit suicide without warning.  

 

Also, ABV = OG - FG x 131.25    where OG is your original gravity reading and FG is your final gravity reading.

 

 

[JoshR 4,697]

Great video! Thanks for sharing, Rick!

[Jim Johnson 1,263]

If you use brewing software check it.  Some of them will do the temperature conversion for you.

[MnMBeer 142]

Thanks Bro,

 

Opens up the aspect of knowing what we are brewing, and when it is done fermenting.

[TheBigDee 0]

Question: After I take the initial specific gravity of the wort, can I use the same sample for future measurements, or must I draw a new sample each time?

[RickBeer 6,214]

Question: After I take the initial specific gravity of the wort, can I use the same sample for future measurements, or must I draw a new sample each time?

 

No.  You drank it, how can you use it again?  

 

Often debated, here's some reasons why you should NOT:

 

- not same temp as beer due to location plus doesn't get the heat off the LBK full of fermenting liquid

- may become contaminated resulting in a different gravity reading

- may have more, or less, yeast cells than the wort so you get a higher or lower reading

- may evaporate differently than the LBK, so it becomes more concentrated, leading to a higher reading

- may get tipped over and break your hydrometer, because they do commit suicide

- you drank it (yes, repeated)

[Bblythe 1]

This may be a silly question but is there a good way to keep the hydrometer from sticking to the side of the test tube?

[JoshR 4,697]

Give it a spin when you put it in the test jar. This will keep it off the sides and it will remove any bubbles that may alter your reading.

[Joechianti 280]

This may be a silly question but is there a good way to keep the hydrometer from sticking to the side of the test tube?

Typical method is to give it a little spin.

[Bblythe 1]

I tried that I think it was in part that my testing area I had the tube on wasn't level so I had to very carefully adjust the tube till the hydrometer was floating straight in the tube. Just wondering if the sticking was a common problem and share my experience.

[RickBeer 6,214]

The tube should be on a level surface, and then as explained you spin the tube if it's leaning against the side.  Any counter or floor is plenty level.

[Bblythe 1]

I was using the counter unfortunately not all houses are plumb and level anymore.

[Jim Johnson 1,263]

ain't that the truth? use your cutting board and pre level it

[Bblythe 1]

That is a good idea

[ba1980 6]

I made an apple cider and the FG went below 1.000.  How would I figure the ABV?

[RickBeer 6,214]

OG - FG x 131.25

[rugercaptain 144]

My hydrometer, God rest its soul, committed suicide on 2/26/15 after giving me an OG of 1.058 on my second batch of CAL with additional malts and hops.  Jumped right off the damn kitchen counter, it did.  Replacement procured; considering obtaining a back-up since they appear to be squirrely. 

[RickBeer 6,214]

Always buy them in pairs, they love to die.

[Jim Johnson 1,263]

My hydrometer, God rest its soul, committed suicide on 2/26/15 after giving me an OG of 1.058 on my second batch of CAL with additional malts and hops.  Jumped right off the damn kitchen counter, it did.  Replacement procured; considering obtaining a back-up since they appear to be squirrely. 

buy 'em in pairs, they seem to get depressed when alone

[Ed H 122]

Most hydrometers are calibrated to give correct readings at 59-60 degrees Fahrenheit. Higher temperatures thin the liquid slightly and result in lower readings than you'd get at the correct temperature. At 70 degrees F., the reading will be 0.001 low. To correct it, add 0.001 to the reading. At 77 degrees F., add 0.002. At 84 degrees F., add 0.003. At 95 degrees F., add 0.005. At temperatures above 95 degrees F., you risk killing your yeast and losing your beer. If you can't remember all that just print out the chart below.

Another thing you need to know is that most hydrometers come with three scales. Specific Gravity, Balling, and Brix are the ones that are usually on your hydrometer. Specific Gravity and Brix are the ones that are most used. Sugar can be measured as ounces per gallon, or as degrees Balling, or Brix. Ounces per gallon are measured on a numeric scale in which an S.G. of 1.046 equals 16 oz. (one pound) of sugar per U.S. gallon. Brix is measured as a percentage of sugar by which pure water has a Brix of 0 (or 0% sugar), an S.G. of 1.046 equals a Brix of 11.5 (11.5% sugar), and an S.G. of 1.095 equals a Brix of 22.5 (22.5% sugar). If you have a choice and want to simplify your life, buy a hydrometer that measures sugar by ounces per gallon.

That should cover everything you need to know about your hydrometer and how to use it. Here are a few tools that may help:

Handy Tools:

Brix/SG Conversion Calculator

Hydrometer Temperature Adjustment Calculator

Cheers!

 

 

 

 

When you speak of the temperature the hydrometer is calibrated, that would be the temperature of the wort and not room temperature?

[RickBeer 6,214]

Yes, wort. Normally the adjustment is .001 or less, so a reading of 1.06 becomes 1.061. Usually makes little diff. And if you pitch at 64 and are done at 64, adjustments negate each other.  In other words, you are adjusting OG and FG for temps different than the hydrometer is calibrated at.  Then you take OG, subtract FG, and multiple the result by 131.25.  Therefore, if both OG and FG were taken at the same temperatures, regardless of how you adjust them the difference is the same as if you hadn't adjusted them.

 

In reality, it really doesn't matter a hoot for most of us.

 

Example:

 

OG of 1.060, temp of 70.  FG of 1.008, temp of 64.

 

ABV UNADJUSTED is 1.060 - 1.008 x 131.25 = 6.825%.

 

ABV ADJUSTED = (1.060 + .001) - (1.008 - 0) x 131.25 = 6.956%.

 

Does it really matter if you're 6.8% ABV or 7%?  And did you then adjust for the sugar when you carbonate?  

 

When it matters is if you start with wort or end with wort that is very different in temperature.  

[Husker Brew 0]

Do you take the OG before you add the yeast or does it matter? And how do you measure whether your beer is done? Is it just when it measures the expected ABV for that certain beer?

[Jim Johnson 1,263]

before

[Jim Johnson 1,263]

how it works is you take 2 readings 48-72 hours apart if they haven't changed it's ready to bottle.  here is an ABV calculator, http://www.brewersfriend.com/abv-calculator/

[Husker Brew 0]

Thanks!

[Keith'sBrew 54]

Thanks for the article!  One of my first purchases as a new brewer was a hydrometer.  The scientific part of my brain hungered for the data.  However, if you follow the 3-4 rule and control your temperature, it isn't a necessity.

[Ed H 122]

One of the first steps in checking FG is to sanitize the tube and hydrometer. If you fill the tube from the spigot, take your reading, then drink it, is it really necessary to sanitize the tube and hydrometer? It's obviously not going back into the LBK and I would assume if the equipment has been cleaned properly, it would not affect the reading of the FG

[RickBeer 6,214]

There is no reason to sanitize a clean hydrometer and tube if you're not putting it back in the LBK, and you should only put back the OG sample, not the FG sample, which would stir things up again.

[Brewer 138]

Perhaps a dumb question but to take a sample from 2 gallons to see if the gravity is stable means taking at least two and possibly three fairly significant amounts of beer from a relatively small batch... I know that brewers have apoplexy at the idea of anyone returning a sample to the fermenter.. so my question: given the propensity for hydrometers to break and given their cost (about $7- 10 a pop) and given the fact that you should not return the sample to the hydrometer does it make any sense to buy a refractormer (initial cost about $30) since they require only a drop or two of the beer to measure the gravity (using the fact that sugar refracts light differently than pure water)? How easy is it to use a refractometer to measure the gravity of beer after the yeast has been pitched and there is now alcohol as well as sugar in the beer? (I believe that there are calculators on line that convert the Brix scale to FG) - and, does anyone know if the hops in the beer will distort the reading so that it becomes unusable to gauge the gravity to tell if the beer is ready for bottling? I have a birthday coming up and I was thinking of getting myself a gift of a refractometer if they can be used to measure the FG of my beer.  Thoughts?

[JoshR 4,697]

Refractometers are great tools, especially for winemakers (because you can see the brix of any fruit instantly). You can take a final gravity reading, but you have to factor in the alcohol so you'll need to use a refractometer adjustment calculator. But because refractometers are designed for sugar water and fruit juice, not wort, you'll also have to figure the Wort Refraction Index to get an accurate reading. I recommend reading this:

http://www.brewersfriend.com/how-to-determine-your-refractometers-wort-correction-factor/

[Andre Sebastian Moreno 31]

Moving this here instead of a previous discussion with JoshR because this thread is solid on topic and pinned.

To confirm: The current production plastic body Mr. Beer hydrometer for sale on the website is calibrated to 59°F (not 68°F), is that correct? I presume Mr. Beer does not manufacture this hydrometer themselves, they have sourced it from a third party and have either specified a 59°F calibrated hydrometer to the third party, or have been explicitly told by the third party that it is calibrated to 59°F, is that correct? (Many of the specific gravity temp correction calculators specify that "old" hydrometers are 59°F and "new" hydrometers are 68°F. I still have not received explicit confirmation that this is a newly manufactured hydrometer based on the "old" design.)

Also, the Mr. Beer hydrometer video lists the ABV calculation as:

"(OG-FG) x 131"

Why does RickBeer cite:

"(OG-FG) x 131.25"?

[RickBeer 6,214]

Because 131.25 is more accurate... Not that it matters. If OG - FG = 50, then your ABV is 6.5625%, i.e. 6.6%. Use 131 and you get 6.550%, i.e. 6.6%.

My two hydrometers are calibrated to 60, not 68.

[Davz13 0]

Thanks for this video!

 

I knew I wanted a hydrometer to try to figure out my ABVs, so I just purchased one.

However, i had no idea how - or when - to use it (and if you should pour the beer back into the keg or drink it, etc.)

 

To my surprise, my hydrometer arrived today - with no instructions at all.

Unless I'm overlooking them: I didn't see instructions on the website, neither (where I purchased it)

 

But thankfully all of you already asked/answered the questions i was going to ask, and MRB Josh R gave the video, so i'm ready to go!

Great job, forum members!

 

Davz13

 

p.s. Well, 1 question: I didnt feel like waiting for this to arrive, so I started my brew a few days ago. Should I take a reading today - and at the 2 or 3 week mark - to get a guesstimated reading...or should i just wait to use it until my next batch?

(I can at least use it on this brew to see if it is ready to bottle!)

[RickBeer 6,214]

Taking it now tells you nothing. 

[Nightwulf1974 30]

While I know how to use a hydrometer after watching several videos and reading online, the video here is marked "private" and is unwatchable for me.  I'm logged in too.  Maybe it's just me, but I wanted to mention it if it isn't. 

[JoshR 4,697]

9 minutes ago, Nightwulf1974 said:

While I know how to use a hydrometer after watching several videos and reading online, the video here is marked "private" and is unwatchable for me.  I'm logged in too.  Maybe it's just me, but I wanted to mention it if it isn't. 

 

It's not you. That video has gone away for some reason. I have removed it from the post. The video Rick posted still works, though.

[Nightwulf1974 30]

Just now, MRB Josh R said:

 

It's not you. That video has gone away for some reason. I have removed it from the post. The video Rick posted still works, though.

 

Ya, I already knew how to do it, but I digest as much as I can and watch many videos since I've started.  Thanks Josh.  Anything Rick posts is money. 

[hotrod3539 911]

@AnthonyC here's all you need to know on using a hydrometer

[AnthonyC 3,803]

1 hour ago, hotrod3539 said:

@AnthonyC here's all you need to know on using a hydrometer

Thanks hotrod!

[Jdub 2,477]

Since we’re talking about taking a lbk sample I have a question.....after you whisk up the wort/water mix in the lbk do you just take a sanitized something to draw some wort out for OG before pitching? Or do you use the spigot?

 

before bottling after 3 weeks do you take a FG sample and then wait a few days and take another? Do you use the spigot and then resanitize it? Or just take a FG sample while bottling to determine abv and just roll with it? I definitley want a hydrometer. Next time mrb offers free shipping I will throw one in with my order. 

[RickBeer 6,214]

Spigot.