How to use your Hydrometer

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tubby_shaw

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How to use your hydrometer.

A hydrometer is an instrument that measures the density of liquid.

Below is a pic of a hydrometer measuring the density of a sugar solution, in a trial jar.


As brewers we are interested in the amount of fermentables (sugars) that are in solution in our beers wines and ciders.
The specific gravity of plain water will read 1.000, as sugar is dissolved into water the gravity increases, 25g of table sugar dissolved in 1 litre of water will result in a specific gravity of 1.010
This is the specific gravity (SG) of the wort (Beer) or must (Wine).
The more sugar that is present then the denser the liquid will be and the higher the hydrometer will float, this is how the specific gravity can be read from the scale on the stem of the hydrometer.
To read the gravity of a liquid, place a sample in your trial jar and check the temperature of the liquid. Hydrometers are calibrated to a specific temperature. Don't worry if the temperature is different you can use THIS CALCULATOR to get the correct reading.
Making sure that the hydrometer is clean, lower it into the liquid and give it a quick spin to dislodge any bubbles that may have formed on the hydrometer as this will give a false reading.
Looking horizontally across the surface of the liquid, read off the number on the scale that corresponds with the true level of the liquid and not the meniscus, see the image below.



To check that your fermentation has finished take two separate gravity readings 24 hours apart, if they are the same and within your final gravity target then fermentation has finished.

An estimate of the alcohol content of your brew can be calculated by making a note of the SG before fermentation begins and a note of the SG when fermentation has finished.
Ignoring the decimal point subtract the finishing gravity from the starting gravity and divide the result by 7.45.
As an example a wine has a Specific gravity of 1.080 before the yeast is pitched, after fermentation has finished and the wine has cleared the Specific gravity is 0.995, so
1080 - 995 = 85
85/7.45 = 11.4
or 11.4% alcohol by volume.

A beer has an initial gravity of 1.044 and a final gravity of 1.012, so
1044 - 1012 = 32
32/7.45 = 4.29
or 4.3% alcohol by volume

A more accurate calculator is available HERE
 

crazycallum

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I just bought a kit and got a hydrometer with it but no trial jar? What could I use as a trial jar that'l I will probably have in the house?
 

corby_brewer

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crazycallum said:
I just bought a kit and got a hydrometer with it but no trial jar? What could I use as a trial jar that'l I will probably have in the house?

you can always just stick it into your FV.
 

A T

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davesiv said:
crazycallum said:
I just bought a kit and got a hydrometer with it but no trial jar? What could I use as a trial jar that'l I will probably have in the house?

you can always just stick it into your FV.
Sterilise it first :thumb:
 

Trotters

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Ok, sorry if I sound thick BUT, do I take the SG reading as soon as ive added the malt, water, sugar & yeast, i.e. the first day Im making my beer?.

And, when do I take the FG reading?. Is that after ive left it for the required length of time after its fermented ie when im ready to drink the beer?.

Thanks
(theres that many posts on here I apologise if this has been asked before, theres just too many threads to search through)
 

the shadow

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you take you SG just befor you add your yeast. and your FG wen the frement its complet usely over 2 days you will get the same reading. depening on wot it is 1.100 to 9.000 . i take the temp to as it can efect the reading a small bit
 

shearclass

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Using tap water, i last night tried to see what temperature my hydromerter was calibrated for.

Surprisingly, it seemed to be calibrated to read 1.000 at 30 degrees. I thought they were supposed to read 1.000 at about 15 degrees?
 

Aleman

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Sounds to me that you hydrometer is out . . . somewhere on it will be stamped the calibration temperature . . . if it is not 20C It will be 15.6C. . . .Often the paper scale slides around in the tube making them inaccurate. A gentle tapping on a firm surface (I use the palm of my hand supported on a firm surface) in the direction you want the scale to move can correct this
 

shearclass

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I have another question - thanks in advance for you patience with me and yoru help.

On the instructionsi have for Coopers kits, they say to divide by 7.46, then add 0.5 for the extra fermentation that will occur in the bottle or barrel. The dividing by 7.45 or 7.46 makes little difference, but does anyone know why coopers say to add the 0.5, where as on another kit i ahd, as well as on this forum, this 0.5 is not mentioned?

Makes a difference to me, as if i have a brew of 3.8 %, i'd consider it weakish, but if i had a brew of 4.3% I'd consider it acceptable! :D

Any ideas? Are coopers simply wrong?
 

Aleman

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I use a completely different set of scales and calculations and methods . . . The problem is that there are several ways to do it, and all are 'correct' within a margin of error . . . I use the HMCE tables and method because that is what I grew up with . . . but the calculator in Promash seems to work well as well.
 

Moley

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shearclass said:
Any ideas? Are coopers simply wrong?
In my opinion, yes.

For an ale, priming at half a tsp to the bottle or 1 tsp to the litre, that's about 4g to the litre which will give about 0.15% abv.

For a lager, priming at 1 tsp to the bottle, you might be heading towards 0.3% abv.
 

jampot

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Looking at my stevenson Hydrometer, the paper guide inside it suggests a starting sg of 1074 would give alcohol of about 12% if finished at 1000 but thats way off? More like 9.8%
 

smndvy

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This may be a silly question (I am only a beginner)

I am supposed to take readings at the end of fermentation over two or three days to confirm completion of fermentation.

I am starting with a basic Youngs kit and I have bought a couple of extra bits & pieces such as thermometer, spoon, siphon kit etc, but the FV doesn't have a tap.

Aren't I running the risk of oxygen contamination every time I remove the lid to check gravity, and how can I minimise the risk ?

Should I drop the hydrometer into the FV (sterile of course) where I can't really see a straight line across the surface and get an inaccurate reading, or should I dip a sterile glass in the beer and take a reading in the glass?

The cup would obviously break the surface tention and destroy any protective layer which may have formed over the brew.

any help appreciated

S
 

bigred

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I use a sterilized turkey baster to take a sample. There will be ample CO2 in the FV to protect it until you rack it.
 
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