Faults

Question 1

Smells like green apples

Answer 1

Acetaldehyde

ac·​et·​al·​de·​hyde

Question 2

What causes acetaldehyde?

ac·​et·​al·​de·​hyde

Answer 2

Either poor quality yeast or not enough yeast pitched or time to convert the acetaldehyde into ethanol.

It can also be a result of packing-problems in bottles

Question 3

Smells or tastes like vinegar

Answer 3

Acetic acid

ace·​tic acid

Question 4

What causes acetic acid?

Answer 4

It is a natural part of the brewing process like lambic beers with wild yeast.

In high concentrates it is a bacterial or yeast infection. Bacteria consumes sugars and indicates spoilage of beer or further problems.

Question 5

Smells like sour butter

Answer 5

Acetic + Diacetyl

ace·​tic + di·​ace·​tyl

Question 6

What causes acetic diacetyl?

Answer 6

Dirty beer lines or contamination of the brewery

Question 7

Smells like cooked sweetcorn or stewed vegetables

Answer 7

Dimethyl Sulphide

di·​meth·​yl sul·​phide

Question 8

What causes Dimethyl Sulphide?

also known as DMS

Answer 8

Compounds created during the malting process are converted to DMS when heated. Bacteria contaminating the beer can also create DMS. It can be driven off though evaporation when boiling wort.

DMS is a desirable flavor in some pale ales and lagers.

Question 9

Smells like sweaty old socks or stanky cheese

Answer 9

Isovaleric Acid

iso·​va·​ler·​ic

Question 10

What causes Isovaleric Acid?

iso·​va·​ler·​ic

Answer 10

Old degraded hops.

Old hops loose bitter alpha acids, producing a flovor of cheese, sweat or must.

Characteristic of some IPAs. stanky cheese can come from high bitterness

Question 11

Smells like a Skunk

Answer 11

Lightstruck
(Mercaptan)

mer·​cap·​tan

Question 12

What causes Lightstruck?
(Mercaptan)

mer·​cap·​tan

Answer 12

When Hops are exposed to ultraviolet rays or florescent light. Alpha acids breaks down reacting with hydrogen sulphide produced by the yeast.

The result is Mercaptan.

Mercaptan is the same chemical released by skunks.

Question 13

Smells like blood, tin

Answer 13

Metallic
(Ferrous Sulphate)

fer·​rous sul·​phate

Question 14

What causes Metallic?
(Ferrous Sulphate)

fer·​rous sul·​phate

Answer 14

When raw materials, wort, beer come in contact with poor quality or non-passivated metals.

Passivation is a process that creates a layer of oxide over metals.

Question 15

Smells like cardboard

Answer 15

Oxidised
(trans-2-Nonenal)

Question 16

What causes Oxidation?
(trans-2-Nonenal)

Answer 16

Oxidation occures when oxygen negatively reacts to molecules in wort or beer.

wort needs aeration before pitching so it is almost always cause by unecessarily transfering beer from one vessel to the next.

Too much headspace in bottles can also cause oxidation.

Question 17

Smells like rotton eggs

Answer 17

Sulfidic
(Hydrogen Sulfide [H2S])

sul·​fid·​ic

Question 18

What causes Sulfidic?
(Hydrogen Sulfide [H2S])

sul·​fid·​ic

Answer 18

Sulfide is produced naturally by yeast during fermentation.

CO2 can carry away excess sulphide so conditioning or lagering after fermentation can ensure sulfur smell or taste fades over time.

H2S is an off flavor in most beers but is a signature in Burton Ale.