Hydrometer Reading

[shaunms]

Hello all

So last night I was making a batch of some modified Coopers Stout and I took and initial hydrometer reading filling the tube to about 3/4 with beer. I dropped the hydrometer in and got a reading of 1050. About 20 minutes later I thought I better take a new reading so that I could sure to be accurate with my calculations, I filled the tube up to the brim so that when I dropped the hydrometer in I got a reading of 1042.

I am not sure why I got 2 different readings. I spun the hydrometer to loosen any air bubbles, it was not sticking to the sides either time and I can not imagine that the amount of beer in the tube, whether half full, 3/4 full or 100% full would make a difference.

Anyone know what the heck is happening?

 

[Adamt]

If you drew the sample from your fermenter tap, it is possible you hadn't completely mixed the extract in so it was more dense (more concentrated) at the bottom.

 

[glaab]

maybe you just had some goo in the tap so the first batch was thicker

 

[the_yobbo]

Or you didn't fill the sample container full enough on your first reading and the hydrometer was sitting on the bottom of the container. (I found this out when testing a second hand hydrometer and sample container. The SG reading for water started at 1.000 but then started increasing slowly. I discovered a hole in the bottom of the sample container and water slowly leaking out.)

As a followup beginner question, if there is a potential of having a higher density reading when taking the first sample from the tap, how is this avoided when trying to get an accurate initial reading?

 

[bum]

Thorough mixing and turfing the first 1/4 cup or so. Then test sample temp but if you're calibrating you gear (as above) then you've got a handle on that already.

 

[Pennywise]

IMO the best way to get a correct reading all the time is to fill the fermenter with about 8-10 litres of water then top it up with the wort and some more water to desired volume, proceed to stir/airate the crap out of it. When you take a sample, draw off half a tube, discard, then fill the tube and take reading.

 

[muckey]

stir the heck out of the wort and then run a little out of the tap and discard before you take your sample

 

[Screwtop]

Sorry to appear as the minister for the absolutely bloody obvious BUT - What was the temp of the wort?

 

[Pennywise]

Sorry to appear as the minister for the absolutely bloody obvious BUT - What was the temp of the wort?

It's usually the case though isn't it, could be so obvious some times it doesn't even register. Hot wort sitting for 20 mins in a test tube cools down pretty quick. I reckon you may have hit the nail on the head there Screwtop.

 

[bum]

He's talking about two different samples taken 20 minutes apart. Is there anyway the temp would change enough to drop 8 points in 20 minutes?

 

[Pennywise]

Yeah didn't pick up on that one either, I doubt it would

 

[muckey]

He's talking about two different samples taken 20 minutes apart. Is there anyway the temp would change enough to drop 8 points in 20 minutes?

have to be a huge temp difference for 8 points

 

[raven19]

What is this hydrometer you all speak of?

Grab a refractometer and never look back!

Seriously though, if its a coopers kit then a stabke FG over a couple of days is much more important than the SG, as being a kit it will be around 4- 5 % anyways.

2c...

 

[muckey]

What is this hydrometer you all speak of?

Grab a refractometer and never look back!

there's 1 on every bus!

you need both so you can show off the bling to non brewing plebs and they will see how intelligent and skilled you really are!!!

 

[Adamt]

Seriously though, if its a coopers kit then a stabke FG over a couple of days is much more important than the SG, as being a kit it will be around 4- 5 % anyways.

I foresee yeast dropping out due to low temperature and a new brewer bottling at 1.030...

KERBLAMMO!

 

[muckey]

I foresee yeast dropping out due to low temperature and a new brewer bottling at 1.030...

KERBLAMMO!

the new face of terrorism h34r:

 

[Screwtop]

have to be a huge temp difference for 8 points

You have a point. Shake the hydro a bit, to be sure the paper sleeve inside isn't loose and giving the crazy readings.

Over the years using a hydro have seen some pretty weird readings returned at warmer temps though. These things aren't rocket science just a displacement device that you dunk in liquid and calibrate at a given temp for a known density value. Just guessing that a Hydro (calibration 15) would give a distorted reading at say 36C of about 6 points.

Screwy

 

[Supra-Jim]

True, but from memory the warmer the temp (above the calibrated temp of the hydro), the lower the reading on the hydro???

OP read 1050, then his OG dropped to 1042?

Cheers SJ

 

[Pennywise]

Isn't it the other way round?

http://www.howtobrew.com/appendices/appendixA.html

 

[buttersd70]

warmer sample, higher reading....
according to beersmith;
for a 15c hydro, 1050 @ 42C = 1042 @ 15C
for a 20c hydro, 1050 @ 45C = 1042@ 20C

In either case, thats a hell of a temp difference required.