[MNWayne]

To prevent suck-back when I cold crash I usually swap out the airlock with a spunding valve before I do my D-rest.  That way I build a little pressure in the headspace and eliminate negative pressure when the temp drops.  Does this affect my FG when measured with a hydrometer?

[lupulus]

No, but you need to de-gas the sample as if it were finished beer.

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[TXFlyGuy]

To prevent suck-back when I cold crash I usually swap out the airlock with a spunding valve before I do my D-rest.  That way I build a little pressure in the headspace and eliminate negative pressure when the temp drops.  Does this affect my FG when measured with a hydrometer?

We eliminate this problem by employing Old World fermentation technique...open air. Works quite nicely for the Pilsner Urquell Brewery. Yes, this is an actual photo of beer ferementing in a barrel, at the Pilsner Urquell Brewery!

[Copymutt]

I'm quite envious of that barrel and its contents. 
Charred oak maybe? Or beachwood?
The more primitive methods are intriguing, My Finn buddy makes Sahti with juniper foilage.

[narvin]

To prevent suck-back when I cold crash I usually swap out the airlock with a spunding valve before I do my D-rest.  That way I build a little pressure in the headspace and eliminate negative pressure when the temp drops.  Does this affect my FG when measured with a hydrometer?

We eliminate this problem by employing Old World fermentation technique...open air. Works quite nicely for the Pilsner Urquell Brewery. Yes, this is an actual photo of beer ferementing in a barrel, at the Pilsner Urquell Brewery!

I’ve done open fermentations but always keg before fermentation is complete.  Yeast does an amazing job of eliminating oxygen but if you cold crash at the end of fermentation sitting out in the air you will inevitably have some major oxidation issues.