Band-Aid (chlorophenol): You just know something is out of whack when
your beer smells of adhesive bandages. This aroma also may remind you of
disinfectant or diaper aromas. It's the artificial quality that really
stands out in this defect, which usually is caused by a problem with
sanitizers or yeast.
Butter or butterscotch
(diacetyl): Think of that artificial butter aroma and flavor from
movie-theater popcorn, and you've got the diacetyl character in some
beers. At low levels, this can be an enjoyable flavor component. But
just like popcorn that's swimming in butter, too much can make for an
unpleasant experience. Beers with too much diacetyl often are called
"butter bombs," and the cause is often a problem with the yeast and
Cardboard (oxidized): The aroma
usually will remind you of wet cardboard or wet paper, like if you left a
box out in the rain and then took a whiff of it. Sometimes, it may seem
leathery. It can be a sign of boiling too long, but more often it's
simply stale beer that's too old or been stored improperly.
Cheesy (isovaleric acid): If you get a whiff of bad cheese or stinky
feet, use your own to run away. It's a doozy. It can have a benign
origin, such as the poor storage of hops, or it could be a bacterial
Cooked corn or cabbage
(dimethylsulfide): Often called DMS, if this is in your beer's nose,
it's probably a sign of something gone awry, especially in ales. It also
may have an asparagus or vegetal smell. In dark beer, the aroma may
remind you of tomato soup. Its cause is commonly a grain infection or
brewhouse problem, which usually occurs in the boil.
Green apples (acetaldehyde): If you smell green apples or green leaves,
it's most likely a sign that the beer was released too soon, or that
there was a yeast metabolic problem. Like its aroma, the beer is a
little green. While usually evidence of a defect, it's not as unpleasant
a problem as many others.
mercaptan or isopentyl mercaptan): A beer can become lightstruck,
causing it to smell like a skunk; it happens almost instantaneously when
it encounters light, especially UV rays. Fluorescent lights and bright
sunlight are common culprits. Since both clear and green glass offer
much less protection, many popular brands of beer are very susceptible
to this problem. Brown glass, while not perfect, offers the most
protection of any common glass color, which is why most brewers use this
for their bottles.
metallic): It's important to note that this would hardly ever come from
canned beer. The metal turbidity that once caused metallic flavors to
leach into canned beer has been virtually eliminated. Today, can
manufacturers spray an organic polymer inside the can so that the beer
literally never touches the aluminum. Metal flavors in beer are usually
bitter, and they're always bad, caused primarily by iron, copper or
other metals in the water.
The aromas in your beer should never seem artificial, and that's what
phenolics smell like. They have an artificial aroma that can take the
form of something medicinal, mouthwash or plastic, and they're cause is
often a problem with the water, yeast or sparging
Rotten eggs (sulfitic): Rotten eggs can be a sign of a serious problem
of contamination, especially when the smell is overwhelming. By
contrast, it can be highly desirable when it's just a very faint or
subtle whiff, more like a burned match. Many ales that were originally
brewed in Burton-on-Trent in the United Kingdom famously had this
character. If it's overpowering, it most likely signals a yeast problem,
or sometimes it's a sign that a beer is too green.