Beer Darkening In Bottles

[BIGRUGBY]

This is a complete mystery to me and I am needing some of your guys help!
I new-ish to brewing, brewed ~5 1-gal extract batches and 2 5-gallon all-grain batches. Been working a lot of hours, making some money, enjoying this hobby, and would like to upgrade my equipment from a turkey fryer biab system with a fermentation bucket, to stainless kettles, mash tuns, a stainless conical, and a kegging setup. BUT, I don't want to spend a whole bunch of money if I still can't fix this issue.

My last batch I brewed an all-grain Tank 7 Belgian Farmhouse Clone. Prior to bottling it was a bright hay color. A month after bottling it had a very clear look to it with a slightly brownish color. I poured a bottle last night and I swear I found a bottle of a brown ale from a couple batches ago that I forgot to drink. This isn't the first time the last few beers in my batches have looked like a light brown colored paper bag. Now, here's the mystery- the vibrant Belgian yeast smell was still there. Taste- totally drinkable, it didn't taste as fresh as the first, but it was no where near tasting like a brown paper bag which leads me to think it isn't an oxidation issue.

Experiments that I have done to try and solve this mystery-
1. Noob mistake, I used to bottle from the autosyphon and have since switched to a bottling bucket with wand. Made a heck of a difference and now that most of the flavor is still there, only slightly altered, I'm thinking it isn't oxidation.
2. I bought some camden tablets (also the same batch I switched to all-grain) and it made a heck of a lot of difference as well, thinking cloramine was my issue.
3. My next experiment, getting an official bottling bucket. I have been bottling straight from my primary fermenting bucket to minimize oxidation. Maybe it is the sediment in the bottom of the bottles that is adjusting the color with the more time the beer sits on top of it??? Should I not be that worried about the risk of oxidation in the additional step from primary to bottling bucket?

Thanks in advance!

 

[Yooper]

It's definitely a classic sign of oxidation. The first sign is a loss of bright fresh flavor, and then as it gets more pronounced with time it might get some vinous or 'sherry' time notes, and when it gets older it will get more like a 'brandy' type of flavor. It has to be very extreme to taste like the described 'wet cardboard' flavor, but if you age a few of those bottles, you'd likely get that in 6 months or so.

It could happen anytime post-fermentation, but worsens with time. So make sure your are doing everything you can to avoid contact with oxygen once fermentation slows. That means perfecting your siphoning techniques, as a start. The autosiphon helps, but it can still get some bubbles, especially when you pump it.

 

[TandemTails]

How long did you let it sit in the bucket before bottling? Buckets work well enough, but they're notorious for not having an air-tight seal.

Bottling from an autosiphon is probably where a lot of the oxygen came into the beer though. Try getting a bottling bucket and a bottling wand and that will probably fix most of the oxygen issues.

 

[BIGRUGBY]

The last two batches (6 and 7) I haven't used an auto siphon to do anything in order to avoid oxidation, post fermentation anyways. Bottling from the autosiphon was my rookie mistake in batches 1 and 2.

My process:
Transfer from kettle to fermentation bucket with spigot, stir vigorously with whisk to oxygenate it for happy yeast.
Carry bucket down stairs for cooler fermentation.
2 weeks later, carry bucket upstairs, let sit overnight for sediment to settle back down, connect bottling wand to fermenting bucket spigot, gently stir in priming sugar, then bottle and cap.

I doubt that it is sloshing that much carrying the bucket upstairs or when gently stirring in the priming sugar. Do I need to make sure my fermenting bucket is full minus the krausen space? Instead of stirring in disolved priming sugar, could I add a teaspoon of sugar to each bottle to annex the stirring? My next thought would be that I am filling bottles to the full-ness of commercial beers, should I fill it within a half inch of the top of the bottle? Could me adding a mesh bag of hops for dry hopping be doing me in (it involves opening the lid of the fermenter to add it)?