Correct Sg Temperature

[Mercs Own]

John Palmer says that 16 degrees is the correct temp for accurate hydrometer readings. Is this true if not what is the optimum temp for hydrometer readings?

 

[tangent]

i can't believe you haven't bought a refractometer yet Merc!

I always heard it was 20C for hydrometers

 

[Justin]

Your hydrometer should have written on it what temperature it is calibrated for. Most are 20'C.

Promash can also do temperature corrections for you and they are quite accurate. Take a gravity reading while sparging, stick in your thermometer and hydrometer and then stick these values into Promash to get your corrected SG. Just watch you don't melt your hydrometer tube.

Cheers, Justin

 

[RobW]

What Justin said. More here:

http://byo.com/mrwizard/1002.html

 

[Doc]

I used this online correction calc the other day as I only got my wort down to 30deg when I took the reading.

Beers,
Doc

 

[wessmith]

Gidday Paul, it should be marked on the hydrometer but they tend to vary a bit. Some are 20C but there is not much variation around the 18 to 20 mark anyway. My Carlton brewers set is 20C as is the cheapie from the HB store.

Wes

 

[wessmith]

Doc, those compensation tables are very inaccurate due to the fact that the hydrometer is calibrated at the one temp only. Higher temps cause the air inside to expand so I'm told and that can affect the reading.

Always try to get the wort temp down to the calibration temp.

Wes

 

[Darren]

There right Merc,
Should say on the side of it what it is calibrated to. Doc's link is good for brewing in summer.
cheers
Darren

 

[Mercs Own]

Thanks guys!! I felt a little silly asking but now I know. I checked my hydrometer and it has the figures; sp gr 20/65 so I reckon that means it is calibrated at 20.

No I havent got a refractometer yet!! Waiting for the next bulk buy as I dont have a pay pal account.

 

[dreamboat]

Not saying that you are wrong on this... but it makes no sense to me at all. Unless the glass expands in some way due to a pressure increase inside the hydrometer, which moves the scale... which would have to be a very minor effect if at all.
The air can't go anywhere, so the mass can't change.....



dreamboat

Higher temps cause the air inside to expand so I'm told and that can affect the reading.


Wes

[post="100780"][/post]​

 

[sosman]

And of course there is my hydrometer correction web form ...

http://brewiki.org/cgi-bin/sgform.py

From what I gather, 20 C calibration temp seems pretty common here and maybe the 16 C (60 F) more common in the US - I'm not really sure.

Oh yes and Brewsta automatically corrects for you but it is hardwired to a 20 C calibration temp at the moment.

 

[Darren]

db,
Does it correlate to the viscosity of the wort? I dunno. (ie if it is warmer does the weight weight sit slightly lower)

 

[sosman]

Not saying that you are wrong on this... but it makes no sense to me at all. Unless the glass expands in some way due to a pressure increase inside the hydrometer, which moves the scale... which would have to be a very minor effect if at all.
The air can't go anywhere, so the mass can't change.....

Dreamboat, nearly all materials expand to some extent with heat so presumably there is some correction required for the expansion of the glass bulb.

According to the table at http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thexp.html for glass it is bugger all so it can probably be ignored.

I know that I have had some whacky readings when correcting hot wort readings but I don't know the reason. Since I use a refractometer now it isn't an issue for me. I do use my hydrometer during fermentation (need to taste a sample).

 

[wessmith]

Dreamboat, I am a little hazy on this and am trying to recall a long converation I had with the guru at Carlton in Brisbane who make the pro hydrometers. There is a HUGE difference in bulb diameters betwen different makes and that can lead to major differences in calibration. At the end of the day, any given hydrometer is only accurate at its rated temp and the various compensation tables can only apply to a particular type of hydrometer. When I asked Carlton for their comp tables he said they dont have any. Just cool the sample to the rated temp.

Simple I guess.

Wes

 

[Darren]

So nothing to do with the viscosity of the wort?

 

[sosman]

Dreamboat, I am a little hazy on this and am trying to recall a long converation I had with the guru at Carlton in Brisbane who make the pro hydrometers. There is a HUGE difference in bulb diameters betwen different makes and that can lead to major differences in calibration. At the end of the day, any given hydrometer is only accurate at its rated temp and the various compensation tables can only apply to a particular type of hydrometer. When I asked Carlton for their comp tables he said they dont have any. Just cool the sample to the rated temp.

Simple I guess.

[post="100828"][/post]​

Is it difficult to argue with someone who makes the things but the calibration tables that I am aware of simply adjust for the density of water at different temperatures which is a well established physical property of water. If the bulbs indeed are temperature stable (or much more so than water) then these tables *should* be accurate.

 

[wessmith]

Sosman, the other physical parameters are changing as well and that I think that is the problem.

Wes

 

[hupnupnee]

So nothing to do with the viscosity of the wort?

[post="100831"][/post]​

Darren, it has everything to do with the density (Viscosity) of the wort. As the temperature increases the density decreases, therefore more wort needs to be displaced to hold up the hydrometer (Archimedes). Thus the specific gravity decreases.

I have a smallish equation that can be used to calculate the SG at certain temperatures if anyone wants it. However it should be realised that the SG calculation is based on an attempt to do a regression of a curve. The problem is that the SG versus Temperature curve is not nice and smooth. In fact the best thing to use if you are desperate to get an accurate SG standardised to a specific temperature is to either use a standard table or better still create you own (yea right!). 1. take SG at say 20* then at 21*, 22* and so on for pure water. (Or your wort if you want). The resulting table is you conversion table. Just add the number on to your measured SG. Sounds like blah really


Cheers

Tim :unsure:

 

[Ducatiboy stu]

Drop your Hydro in a glass of distilled water (or tap water )and read the temp of the water when the hydro is sitting at 1000. That way you will know what temp to do your reading at....

 

[Darren]

hi Hupnupnee,
Thanks. Thats what I thought. Proteins passing through a sucrose density gradient obey similar principles.
cheers
Darren