Part III, Section C: Phenols, Esters and Off-Flavors in Beer

Question 1

What are the 6 aromas and flavors caused by oxidation in beer?

BES Card #208

Answer 1

1. Stale
2. Old, wet cardboard
3. Papery
4. Winelike
5. Sherry
6. waxy, lipstick

Question 2

What is ‘skunked’ or light-struck beer

BES Card #209

Answer 2

Beer becomes skunked when light (specifically the blue spectrum of sunlight or fluorescent light) comes in contact with the compounds that produce hop bitterness, producing a chemical called MBT. MBT is one of the most powerful flavor substances known to man. The pungent odor compound resembles that of the famously malodorous defense spray deployed by skunks.

Question 3

What are the 4 aromas of lightstruck beer?

BES Card #210

Answer 3

1. Skunk
2. Must (a stale, stuffy smell. Your damp basement and dry, hot attic might both smell of must.)
3. Burnt rubber
4. Cat musk (Cats have two anal glands, one on either side of the anus, that produce a musky or fishy smelling material.)

Question 4

What are 2 flavors associated with dirty draft lines?

BES Card #211

Answer 4

1. Butter
2. Vinegar

Question 5

What are the 3 aromas and flavors of diacetyl contamination in beer?

BES Card #212

Answer 5

1. Butter
2. Rancid butter
3. Butterscotch
   Also: slick mouthfeel

Question 6

Esters: what is the flavor of Isoamyl Acetate?

Answer 6

Banana; ‘Peardrop’

A pear drop is a hard candy popular in England, and it gets its flavors from an ester called isoamyl acetate. Why is that important? Well, esters are aromatic chemical compounds that are found both in wine and in certain foods. So if someone smells “pear drop” in their wine, they may indeed be identifying that ester.

Question 7

Esters: what is the flavor of Ethyl Acetate?

Answer 7

Lightly fruity, solvent-like

As ethyl acetate intensifies, however, the aromatic perception can skew from pleasant and fruity to solvent-like and perfumy; abnormally high levels are therefore regarded as off-flavors. In addition to being produced by brewer’s yeast strains (Saccharomyces cerevisiae and Saccharomyces pastorianus), ethyl acetate is also produced in large quantities by the wild yeasts Brettanomyces, Hansenula, and Pichia via aerobic fermentation.

Ethyl Acetate is widely used in glues, nail polish remover, and other household solvents.

Question 8

Esters: what is the flavor of Ethyl Caprylate?

Answer 8

Apple; fruity, floral, banana-like, pineapple-like, or even brandy-like in its pure state

Ethyl caprylate (also known as ethyl octanoate), contributes to beer aroma. It tends to go hand in hand with the development of a yeasty flavor that may or may not be desirable, depending on the concentrations and the style of beer

Question 9

Esters: what is the flavor of Ethyl Caproate?

Answer 9

Apple-like with a note of anise; sometimes pineapple

Also known as Ethyl hexanoate

Question 10

Esters: what is the flavor of Phenyl Ethyl Acetate?

Answer 10

Roses, Honey

Question 11

Phenols: what is the flavor of 4-Vinyl Guiacol? (4VG)

Answer 11

Clove

Produced as a by-product of ale yeast in fermentation. Has a clove flavor, and is an important component flavor in hefeweizens but is seen as an off-flavor in most cases

Question 12

Phenols: what is the flavor of Guaiacol and Syringol?

Answer 12

Smoke

These phenols are created not by yeast activity, but by kilning over wood fire and exposure to the smoke, as in rauchbier. These give a beer a smoky aroma and taste, sometimes described as campfire or barbecue potato chips.

Question 13

Phenols: what is the flavor of 4-Ethylphenol (4-EP)?

Answer 13

farmyard, medicines, horse blankets and mice

This phenol is produced by the wild yeast type Brettanomyces and it reminds people of farmyards, medicines, horse blankets, and mice. It is seen as an off-flavor in most cases but a component of some Belgian ales and lambics. It is also found in arabica coffee.

Question 14

Phenols: what is the flavor of 4-Ethyl Guaiacol?

Answer 14

Smoked meat, clove-like spicy character

Produced by Brettanomyces, and seen as an off-flavor in most cases. It also has interesting woody and sweet vanilla nuances.

Question 15

What produces the flavor of banana or ‘Peardrop’?

Answer 15

An ester: Isoamyl Acetate

Question 16

What produces flavors that are light fruity or solvent-like?

Answer 16

An ester: Ethyl Acetate

Question 17

What produces the flavor of apple; fruity, floral, banana-like, pineapple-like, or even brandy-like in its pure state

Answer 17

An ester: Ethyl Caprylate (also known as ethyl octanoate)

Question 18

What produces the flavor of Apple-like with a note of anise; sometimes pineapple?

Answer 18

An ester: Ethyl Caproate (also known as ethyl hexanoate)

Question 19

What produces flavors of roses or honey?

Answer 19

An ester: Phenyl Ethyl Acetate

Question 20

What produces the flavor of clove in hefeweizens?

Answer 20

A phenol: 4-Vinyl Guiacol? (4VG)

Question 21

What produces the flavor of smoke, or smokiness?

Answer 21

Two phenols: Guaiacol and Syringol

Question 22

What produces the flavor of farmyard, medicines, horse blankets, or mice?

Answer 22

A phenol: 4-Ethylphenol (4-EP)

Question 23

What produces the flavor of smoked meat, or a clove-like spicy character?

Answer 23

A phenol: 4-Ethyl Guaiacol

Question 24

How can you mitigate solvent-like off-flavors in brewing?

Answer 24

Solvent off-flavors are caused by out-of-control ester production. Ester production is increased at higher fermentation temperatures so often we will find solvent off flavors when a beer is fermented too hot.

To mitigate solvent-like off flavors you need to choose a yeast that has your desired level of ester production and also control the fermentation temperature to make sure it does not rise too high.

Question 25

What produces the ‘green apple’ off-flavor in beer?

Answer 25

Acetaldehyde

Acetaldehyde, also called ethanal (note different spelling from ethanol) , is a common compound that comes in everything from ripe fruit to coffee. It is also an intermediate compound produced by yeast during fermentation. As fermentation progresses to completion, all of the acetaldehyde is normally converted to ethanol which is the alcohol in beer.

Question 26

What is the flavor/smell of dimethyl sulfide (DMS)?

Answer 26

Cooked or creamed corn

Question 27

What causes the flavor/smell of cooked or creamed corn?

Answer 27

Dimethyl sulfide (DMS)

Question 28

What off-flavor does Acetaldehyde produce?

Answer 28

Green apples

Question 29

With bottle-conditioned beers disturbing the yeast sediment can produce off-flavors. Old yeast sediment can become ‘autolyzed’. What would these flavors be?

Answer 29

Ground meat past prime or tire rubber