Reading the section on brewing first will enhance your understanding of this section. Click here for "A Brief Treatise on Brewing."
Many things contribute to the flavor, aroma, "mouth feel," and appearance of beer. The way that various brewing ingredients and techniques affect these characteristics are discussed here.
Water
Malt
Specialty Malts
Hops
Yeast
Flavorings
Malted barley is the standard beer grain, but wheat, corn, rice,
oats, and other grains are mashed along with at least some barley
(which contains the enzymes necessary for breaking down the starches
into fermentable sugars) in many beers. These grains, as
well as sugars such as sucrose and dextrose, can be used as
adjuncts. Used in place of malted barley,
they will give the beer a lighter body.
The amount of malt extract in the wort affects the color:
small amounts
of malt yield a light-colored beer; a large amount of light malt
or a lesser amount of amber malt with yield an amber (and perhaps
red-hued) beer;
and a lot of any malt, but especially a dark malt, will yield
a dark beer.
The color is also deepened by the addition of specialty malts
near the end of the boil.
The more fermentable sugars from the malt there are present in the wort,
the more available to be fermented into alcohol. Provided
that nothing kills the yeast (such as the alcohol concentration
getting above about 9% by volume), all fermentable sugars will
be converted into alcohol.
The other carbohydrates present will not be fermented, but will
give the beer body and color.
Higher-order sugars from the malt, and certain intentionally added
sugars, such as lactose, are not fermentable by brewing yeasts
and will cause a sweetness in the final beer. The concentration
of these larger sugar molecules can be increased by mashing
appropriately, as well as by simply putting more malt in the wort.
Dextrins, on the other hand, do not cause a sweet taste,
but give the beer a slightly more viscous (less watery) "mouth feel."
The concentration of dextrins can also be controlled during
mashing, as well as by the addition of specialty malts.
Here arises a point about the relationship between beer color and
alcoholic strength. Popular belief holds that darker beers are
stronger. There is a correlation, but if the malt was dark to
start with, or if specialty malts made the wort darker,
a dark beer would have the same strength as a light-colored beer
that started with the same concentration of fermentable sugars.
In modern times, the most important functions of hops are to
give a bitterness that balances the sweetness of the malt and
to provide a "hoppy" aroma, especially noticeable in highly
hopped beers such as India pale ales.
Hops varieties vary in bitterness, containing from 4 to 13%
alpha acid. More hops in the wort results in more bitterness,
as does boiling for longer in a more dilute wort (this is
referred to as "hop utilization rate").
Hops strains also vary in aroma. This is harder to quantify,
but again, more hops added late in the boil yield more hoppiness.
Water
The major ingredient in beer, water is the least significant.
Water varies with location as to what is dissolved
in it. Organics, dissolved gases, and inorganics are three
broad categories.
Volatile organics and gases (such as the chlorine used in
sanitizing municipal water supplies)
are driven off when the wort is boiled.
Unless they occur in unusually high concentration,
the salts in water used for brewing do not have
a discernible taste in the final beer.
Acidic or basic inorganics in water, of course, affect the pH.
Brewers doing mashing must pay attention to this
and adjust it if necessary.
Incidentally, some minerals are desirable,
as they provide nutrients needed by the yeast.
Malt
Malt is the oldest and most important ingredient
in beer. Without malt, there would be nothing to ferment!
Ancient beers were created with only two known ingredients:
water, and malt or some other source of fermentable sugar
(such as honey, which is used in mead). Wild yeast was responsible
for the fermentation.
Specialty Malts
Most specialty malts start as malted barley,
which is roasted to various
degrees, resulting in darker colors ranging to black.
The darkest of these, black patent malt,
primarily adds color to the beer.
"Chocolate" malt is roasted less, and will give the
beer a chocolate-coffee flavor, as well darkening it.
These malts are not mashed and do not contribute
fermentable sugars to the wort.
"Crystal" malt, on the other hand, is partially mashed in the kernel,
and will add fermentable and unfermentable carbohydrates.
The unfermentable higher sugars and dextrins are important in
adding to the sweetness and less-watery mouth feel of the final beer.
These whole barley kernels are crushed and steeped in warm wort,
after which the husks are removed. An alternative method is
adding near the end of the boil.
Adding during the boil is a common
practice, but the husks can add tannins and other chemicals
that lend a harsh bitterness (different from the hop bitterness)
to the beer.
Hops
Hops were originally added to beer as a preservative.
During fermentation there are many carbohydrates in the wort
that bacteria could thrive on. Bacterial infections give a nasty
taste to beer and are obviously undesirable. The acids released
by the hops kill most such bacteria. The hop acids continue
to protect the unfermentable (by yeast) sugars from being digested
by bacteria that may have gotten into the finished beer.