Originally Posted by grndslm
I am not 100% sure where I read about the brewers who rolled the lager carboys on the ground, but I'll try to find it.
I'm definitely going to cease replying until I have finished this Yeast book, however. So...
I know the OP said he's "out" so that's fine. but something was bugging me about the color change described. During brewing this afternoon, it hit me!
The wort color will be the finished beer color. It can't get darker or lighter - except for while there are hundreds of billions of yeast in suspension and then it will get back to its original color after much of the yeast falls out and the beer clears.
If the beer darkens, and it's not attributable to the yeast falling out of suspension, it is probably due to oxidation. One of the classic signs of oxidation is a darkening of the beer.
For example, I brewed today. Here is a photo of my hydrometer sample. I'm by the light because I want to check color and clarity.
It's not a great picture, because of the light streaming in the window, but I think it illustrates my point. The beer will be this color when it is finished. It has to be. It can not be darker, and it cannot be lighter once it clears.
The OP stated that the beer went from light yellow to dark rusty. If it turns rusty or dark colored, it almost is certainly oxidation.
(Look at all that cold break in the bottom of my test jar!)