Same grain bill, water profile, technique, etc - waaaay darker wort

Liked a batch (Belgian-style Tripel) and decided to re-brew it. It had the same:
- grain bill
- water source (distilled) and profile
- strike/sparge water volumes
- LHBS source
- mash and boil time
- equipment

It was different with:
- mash temp; 1 degree lower
- amount of times stirred; since that batch I stir like crazy at first and then let it rest, per the advice of several HBT users, rather than every 10-15 minutes like I used to (I highly doubt this has an effect as I have not noticed it on the several IPAs I have brewed since switching methods)

It appeared darker at every stage including the first runnings all the way to the original gravity sample. It appeared darker regardless of vessel (gravity sample, half gallon measuring cup for vorlaufing, carboy), so it isn't just me seeing it in a different vessel this time - it was noticeably darker at every stage and in every vessel. I would say the first batch's original gravity sample was around 6-7 SRM while the second batch's was around 12-13.

I'm not worried about it as I am sure it will be tasty regardless of color, but it is quite curious as almost everything about both batches was the same. Outside of my LHBS accidentally giving me dark wheat instead of wheat (or something like that), which I highly doubt, I can't think of anything. Thoughts?

"Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."

Might more stirring lead to more oxidation, thus more darkening of the wort?

Or, is there a variation in the malt (season to season, batch to batch, maltster to maltster) that contributed to the difference? I've had different batches of malt from the same maltster be so different that I wondered if it was the same malt.

Boil time might be the same, but is the boil intensity the same? More intense boil could lead to darker wort.

Maybe you didn't notice it on the IPAs, but maybe you would notice it on a pilsner or a cream ale? Maybe the difference isn't as noticeable on a higher SRM beer.

More questions than answers, but something to think about...

Are you sure you didn't accidentally use black patent instead of pilsner malt?
That would make it quite a bit darker.

Black Island Brewer said:

Might more stirring lead to more oxidation, thus more darkening of the wort?

Boil time might be the same, but is the boil intensity the same? More intense boil could lead to darker wort.

Click to expand...

I had no idea these two things led to darker wort?

YeastFeast said:

I had no idea these two things led to darker wort?

Click to expand...

The first, the stirring causing oxidation, is more of a question. Oxidation will cause a darkening, but does stirring the mash lead to oxidation? I don't know, but it would be an interesting xBeeriment.

The second, heat interacting with protein, sugar and water, will cause darkening. So is a more intense heat likely to cause darkening? I would think so, but again, a good xBeeriment!

Could there have been dark grains milled prior to your milling this batch? Perhaps enough dust got through while you were milling your batch.

If you didn't personally select the grains out of the bins at your LHBS and relied on them to measure and mill; I would lean towards them making a substitution or an error (or possibly the dark grain residue in the mill that @Jhenjum mentioned.). I would doubt it was anything during the mash or the boil to result in such a marked change.

If you want to see how deep the rabbit hole goes WRT wort darkening from the addition of oxygen on the hot side (mashing and boiling), you can pop on over to the AHA forum, where a ̶t̶e̶d̶i̶o̶u̶s̶ ̶a̶n̶d̶ ̶p̶e̶d̶a̶n̶t̶i̶c̶ ̶g̶r̶o̶u̶p̶ ̶o̶f̶ ̶b̶e̶e̶r̶ ̶n̶e̶r̶d̶s̶ bunch of homebrewing enthusiasts are continuously extolling the virtues of low oxygen brewing. It is reminiscent of the batch sparge vs fly sparge debates that spanned pages and years back in the '90's.
https://www.homebrewersassociation.org/forum/index.php?topic=27965.0