Hydrometer reading

Hi,

I've been reading "The New Complete Joy of Home Brewing by Charlie Papazian" .

In it he mentions that hydrometers give accurate readings at 60 degrees F.
He says for every 10 degrees above that you have to add .004-.006 to the reading (my decimal points may be wrong but you get the idea).

I haven't read this anywhere else and when I questioned another homebrewer he said: " I just drop my hydrometer in the liquid take a reading and don't worry about it, then I take my final gravity and that's that. All I worry about is making it then drinking it" He never heard of the 60 degree thing.

Anyone?

Tommy

Hydrometers are definitely calibrated for a particular temperature. Liquids are denser at lower temperatures so the hydrometer will read differently. However, you can't really say that all are calibrated for 60F...I've seen some for 68F. Also, most of them come with a little slip of paper in the tube which tells what the correction factor at a given temperature is.

If you're going to the trouble to take a reading, might as well get an accurate one IMO.

The gravity readings are affected by temperature and charlie's chart should give you the correct reading..

that being said.. (i'm guessing here, somebody correct me if i'm wrong)
If you take the OG and FG readings at the same temperature then your ABV calculation should still be correct..

if the OG and FG readings are at different temp then it will be off.

and after all is said and done..

you'll still drink the beer

ws

yeah funny thing about specific gravity, it has no units. Its just a ratio between water and whatever your reading. apparently Scientific hydro's are calibrated at 4 degrees C (39.2F) but most beer ones are at 60F, (water should read 1.000 @ 60 degrees)

you could calibrate it yourself by sampling water at 60-70 degrees. You should be around about 1.000 I did this recently and found mine to be 'off' by .002 degrees. (i actually just remembered this as i was writing and now realize my last 2 batches have different readings then what i wrote down, oops!)Once its calibrated it is a really convenient tool.

waskelton4 said:

The gravity readings are affected by temperature and charlie's chart should give you the correct reading..

that being said.. (i'm guessing here, somebody correct me if i'm wrong)
If you take the OG and FG readings at the same temperature then your ABV calculation should still be correct..

if the OG and FG readings are at different temp then it will be off.

and after all is said and done..

you'll still drink the beer

ws

Click to expand...

I was kind of thinking along these same lines. The problem is my math skills aren't good enough to know if that would work out or just make me look stupid
But, if what's being measured is liquid density and this needs to be done at a certain temp, then couldn't the readings be wrong? In other words, maybe the OG and the FG (if both measured at the same temp) will give you a correct reading as far as getting a ballpark calculation or to show that your brew is good to go but not necessarily a "true" ABV reading.

I don't know how or why but it kind of reminds me of the old "what weights more a hundred lbs of bricks or a hundred lbs of feathers?"

Don't mind me, I have no clue what I'm talking about

Tommy

Brewno said:

"what weights more a hundred lbs of bricks or a hundred lbs of feathers?"

Tommy

Click to expand...

Definitley bricks weigh more. Ive done masonry and believe me its much harder on your back to move 100 lbs of bricks then 100 lbs of feathers. (1 brick vs. 1 feather at a time)

Brewno said:

In other words, maybe the OG and the FG (if both measured at the same temp) will give you a correct reading as far as getting a ballpark calculation or to show that your brew is good to go but not necessarily a "true" ABV reading.

Click to expand...

I think (i've only done it once) that the ABV forumla uses the difference of OG and FG.

(OG - FG) * 131 = ABV

or something like that
so if OG and FG are both wrong .. but are wrong by the same amount in the same direction.. then ABV will be correct.

wow.. that was the most math i've done since freshman year college..

and i could be equally as wrong as most of that freshman year college math too

ws

Bjorn Borg said:

Definitley bricks weigh more. Ive done masonry and believe me its much harder on your back to move 100 lbs of bricks then 100 lbs of feathers. (1 brick vs. 1 feather at a time)

Click to expand...

So much for "100 lbs is 100 lbs"


Tommy

Bjorn Borg said:

yeah funny thing about specific gravity, it has no units.

Click to expand...

The unit of specific gravity is Kg/L. It just happens that 1 L of water weighs 1 Kg at 4*C (40F). I usually care about taking an accurate reading. But mostly I just note the temp and the SG reading and let Beersmith do the calculation when I have it around and care for the actual SG value.

Kai

Here's a link to a hydrometer correction utility:

http://hbd.org/cgi-bin/recipator/recipator/hydrometer.html

It's especially helpful in doing AG because need to take the SG of your collected wort which is well above 60 degrees F.

(ProMash and Beersmith do this as well, I'm sure)

I just write down the OG & the temperature. Ditto for the FG. Since the OLCB isn't charging me by the ABV, I don't care much. My main concern is whether or not the fermentation is done.

Let me see if I can grab the correct info from my brain...

My hydrometer instructions says it is "calibrated" at 59F. If, for example, my OG is 1.055 and the temp is 72F then I add .002 (or at 84F I add .003).

So that would be 1.055 plus .002 = 1.057 Corrected OG.

If my Final Gravity (FG) is 1.011 at 70F then it becomes 1.011 plus .002 (in the range) = 1.013.

Subtract the FG from the OG or 1.057 - 1.013 = .043.

Multiply that number by 105 equals 4.515% ABW (Alcohol By Weight).

To get ABV (Alcohol By Volume) you multiply the ABW by 1.25 to get 5.64% ABV.

I hope all that is correct. If not I will correct it tonight.

Does anyone check the runoff using ph instead of gravity? Instead of stopping the runoff at 1.010 or below, would it not be easier to get a ph meter, which isnt affected by temps? (or is it?)

Bjorn Borg said:

Does anyone check the runoff using ph instead of gravity? Instead of stopping the runoff at 1.010 or below, would it not be easier to get a ph meter, which isnt affected by temps? (or is it?)

Click to expand...

pH is temperature dependent.

Lou said:

pH is temperature dependent.

Click to expand...

There are PH meters with temp compensation, but the probe will last much longer if you measure cold liquid.

cweston said:

Here's a link to a hydrometer correction utility:

http://hbd.org/cgi-bin/recipator/rec...ydrometer.html

It's especially helpful in doing AG because need to take the SG of your collected wort which is well above 60 degrees F.

Click to expand...

You should still chill the wort to be measured since the hydrometer may crack in hot liquids.

Kai

I use a glass hydrometer sample jar (whatever you call it)...just turkey baster some hot wort into it and put it in a tall glass of ice water. It's 70F in no time at all.

The link to the converter you posted is awesome thanks. I knew I was keeping daily temperatures in my brew journal for a reason. Now I've gone through and adjusted all my gravity readings and it so makes sense.
Thanks again.