Brett Saison getting darker in keg over time

It could be brett. Sometimes when you keg a beer with a very low floc yeast such as brett, you get extra yeast in the beer near the end of the keg as the volume compacts.

 

Has the keg been kept cold the whole time? Heat will speed up oxidation. Also, if a lot of time has passed, could be there is just more sediment near the dip-tube and as that gets sucked out, you may see a brighter beer?

 

That was my thought as well, a beer will appear lighter with yeast in suspension, as it drops out it will begin to clear and appear darker.

 

Interesting. A friend has noticed similar findings with his IPAs. And IPAs is pretty much all he makes.

He also doesn't go through excessive co2 tanks and the beers don't taste oxidized.

Interesting yeast concept stated.

I'm baffled.

 

I actually think this is opposite of what's true.

Hazy beers with yeasts that just never drop out always appear 1-3 srm darker than a similar grist beer that is brite IMO.

 

Well your photos prove otherwise...I know I've definitely noticed this in my carboys, when a beer is actively fermenting it is quite a bit lighter, than after the yeast floccs. Mostly because yeast is white or cream colored, I'd assume.

 

How much unmalted or higher protein grains were used in the recipe? Could be that the proteins were refracting the light early on making it appear brighter, and then as the Brett breaks them down and they drop from suspension it is appearing darker.

 

@Soneast

100% of the yeast suspended in a carboy produces a different visual effect than extra yeast in a glass.

A "little" extra yeast in the glass will make the beer appear darker. When you keg a beer with a low flocc yeast, the beer can vary between gravy, darker hazy and somewhat clear depending on time, temperature and rate of flocculation. The gravy beer can appear lighter than the darker hazy beer for the same reason as it appears lighter in the carboy. That's because it contains a metric crap ton of yeast!

The pictures in the OP show the same beer in different diameter glasses and different lighting which makes for an invalid comparison. However, it's perfectly clear. Beer number two which is considered to be darker by the OP contains more yeast than beer number one and neither of the pours achieved gravy status.