Deconstruction of beer

Aroma:

Derived from ingredients such as malt and hops but modified and augmented by yeast.

Head:

From the medium-length proteins present in malt and adjunct grains. Affected by mashing , hop iso-alpha acids, and possibly filtration.

Color:

Primarily from kilning of malts chosen for the brew but affected by mashing and boiling, fermentation and filtration.  

Carbonation:

Co2 gas from the fermentation by yeast.

Body:

Proteins from malts, affected by the brewing fermentation and filtering procedures and sweetness from malts.

Alcohol:

More fermentable material means more alcohol.

Taste:

Sweetness, bitterness and acidity are the most important tastes in beer.