Beer Color and Brewing Conditions
Substantial color changes in a finished beer can be attributed to differences in brewing conditions.
Water: As the alkalinity of the water increases, so does the extraction rate of the coloring pigment in the malt. Increasing mash pH has the same effect leading to deeper color as the pH increases.
Mash: Color increases as the contact time with the grain increases. Thus, a prolonged mash will lead to a deeper-colored beer than a short mash.
Kettle Boil: Wort color increases with boil time because the Maillard reaction occurs during the boil. Simmering wort has the same effect and will lead to an incomplete hot and cold break, which in turn leaves more coloring elements in the finished wort.
Hops: Some color is obtained from hops both during the boil and during dry hopping.
Fermentation: The proteinous matter produced during the hot and cold break is full of color. Therefore, its removal will reduce color. It has also been reported that color changes during fermentation vary with different yeast strains .
Filtration: Filtering beer dramatically reduces color. A clear beer will also appear to be lighter than a turbid beer. That's why the fermenting beer in your carboy appears much darker than it does by the time it get to your glass.
Oxidation: At all stages of brewing, air pickup will darken beer color. This is as true of hot wort production as it is in the bottle with head-space air and all steps in between.