Gravity

[Doctormcbrewdle]

Ok. What's up with this

I have an IPA (1.065, 2x M44 yeast sachets) that took off within hours with full Krausen. Brewed at 19 degrees for 7 days then rose to 21 for the past 3. I've taken 3 hydro readings now, all of which are 1.016 but drop to 1.012 within a few hours as the tube sample clears. Why does this happen? I keep just leaving my beers in the fermenter because this happens all the time for me and not sure I can trust the reading because lets face it, it's 4 points above just a few hours prior to clearing in the tube. Is it done, or?

Would be good to find a satisfactory explanation for this

 

[Black n Tan]

I think the most likely explanation is carbonation: CO2 bubbles clinging to the hydrometer and lifting it higher resulting in a spuriously high gravity reading. Spinning the hydrometer can help detach the bubbles, but I also like to move the hydrometer up and down a few times to release some of the gas before measuring.

 

[Doctormcbrewdle]

Nope. I actually plunge the hydro in and out about 50 times to get any air bubbles out and spin hydro before reading

 

[Doctormcbrewdle]

Could it be that it's 33 degrees once in hydro and the increase in temperature is finishing these final few points off quickly? Just a slow finish alot of the time for me in the brew fridge? Could this be oxygenation issues?

 

[Doctormcbrewdle]

Alright, now 2hrs later it's dropping clear and 1.012 Has to be oxygen stuck in the solution as Black mentioned, right?

 

[Lyrebird_Cycles]

Degas the sample and see if the same thing occurs.

Bucket chemistry degassing method: two beakers each with a capacity at least twice the sample volume. Pour sample from one to the other several times: you'll be able to tell by sound when you;ve knocked most of the gas out. Increasing the difference in height between the beakers as you pour speeds this up but increases the chance of missing.

 

[wereprawn]

Temperature differences between fermenting and ambient messing with your reading is your problem. Have a play with this.

https://www.brewersfriend.com/hydrometer-temp/

 

[Doctormcbrewdle]

You know what I think it is now.. the trub is bringing up the gravity because it's heavier than the surrounding liquid. Once it compacts the reading normalises

This 'could' be due to oxygen being trapped in the trub also, but nonetheless it's ok once settled out. Cold crashing now

 

[wereprawn]

It's carbon dioxide bubbles you're seeing mate. If you use the calculator provided, you'll see that when your hydrometer is calibrated to 20c, and your hydro is reading 1012 at a presumed 18c, when the temp rises to 33c the hydrometer will read 1015. Sounds close to what you are noticing, no?

 

[Doctormcbrewdle]

No, it's the opposite man. Reads 1.016 at 20 degrees and the same at 30, until the trub settles

Mine reads 1.012 now at 33 or 20 so not sure the calculator is correct

 

[Lyrebird_Cycles]

Mine reads 1.012 now at 33 or 20 so not sure the calculator is correct

Ya canna change the laws o' Physics, Capn.

Water expands when heated. Same mass in a larger volume = lower density (called gravity by brewers).

It is physically impossible to have the same SG at 20 and 33 degrees in any water based fluid. If your readings tell you this is happening, your readings are wrong.

 

[Lyrebird_Cycles]

Edit:

I'd written a description of how your suppositions on oxygen interference also failed Physics 101 but I see that you said oxygen when you meant CO2, so what I wrote is moot.