How does temp affect SG?

[ShepherdQ]

Hi all,

I started a kit yesterday (CC Showcase WA Merlot), and added the grape pack as instructed, but o gave it a good few squeezes to get as many TDS in the wine as possible. Checked SG: 1.094. Temp was about 18°C (65°F)

Because I figured the sugars et al. from the grapes would continue to dissolve over the next 24 hrs I checked the SG again just now, and it went down to 1.092. I've got the Brew Belt on so temp went up to 20°C (70°F).

No visual signs of fermentation yet, not expecting it to start till tomorrow at the earliest, so could the rise in temp be responsible for the decrease in SG? I know water is more dense at colder temps, but is a hydrometer affected by that?

 

[barryjo]

Hi all,

I started a kit yesterday (CC Showcase WA Merlot), and added the grape pack as instructed, but o gave it a good few squeezes to get as many TDS in the wine as possible. Checked SG: 1.094. Temp was about 18°C (65°F)

Because I figured the sugars et al. from the grapes would continue to dissolve over the next 24 hrs I checked the SG again just now, and it went down to 1.092. I've got the Brew Belt on so temp went up to 20°C (70°F).

No visual signs of fermentation yet, not expecting it to start till tomorrow at the earliest, so could the rise in temp be responsible for the decrease in SG? I know water is more dense at colder temps, but is a hydrometer affected by that?

So you have already pitched the yeast? Fermentation has probably started.
Yes, the SG is affected by temp. If you have the sheet that came with the hydrometer, it gives correction factors for temp. Otherwise, figure about 7 degrees F equals 1 point SG. Given the small change , I wouldn't get too concerned. Just remember to keep very close notes on all you do.
The what, when, how much things are essential to getting a repeat performance.
I adjust the SG before pitching the yeast.

 

[ShepherdQ]

Pitched the yeast right away, I never bother waiting. Huh, I always thought it took a good couple days for fermentation to start. Alright, happy everything is tickety-boo!

 

[Pumpkinman]

Your hydrometer is designed to be accurate at a known temperature, usually 60°, but that may be different for different Hydrometer. If the temperature of the liquid (Wine/Beer)is not at this temperature then the reading will not be accurate. Fortunately the effect is predictable and can be adjusted for. you can find a calculator online that will allow you to plug in the SG and the temp and it'll correct it for you, click here to get the calculator.

 

[ShepherdQ]

Cool, tks pumkinman! That one's going in my favorites.

 

[Pumpkinman]

Always glad to help, I actually downloaded a free app for my android called ABV Calculator, I use it a lot.

 

[ShepherdQ]

Sweet, downloaded. Heard of the winemaker's toolbox app? I've been using it to calculate final alcohol, just noticed it has a SG correction feature too :[

And, having used that, the corrected SG readings are 1.0945 and 1.0931 respectively. Not a huge difference but certainly significant.

Thanks guys

 

[ShawnDTurner]

Visual signs of fermentation are over rated, trust your hydrometer.. cheers