Acetaldehyde

Question 1

Characteristics

Answer 1

Fresh-cut green apples, and sometimes has notes of grass, green leaves or latex paint.

Acetaldehyde is produced in the early stages of fermentation and is reduced to ethanol in the latter stages of fermentation.

If the yeast is not sufficiently active, either because it is not healthy or the fermentation temperature is too low, too much Acetaldehyde will remain in the beer.

Bacterial infections can also interfere with yeast fermentation, leaving elevated levels of Acetaldehyde in beer.

Make sure fermentation is vigorous using healthy yeast. Allow full attenuation. Leave beer on yeast longer. Oxygenate wort fully. Try another yeast strain. Make sure sufficient yeast nutrients are available. Let beer age longer.

Question 2

Describe/Discuss

Answer 2

• Green apples
• Grassy
• can taste and small acetic (vinegar) / cidery

EVER APPROPRIATE?
- Yes, at low levels

IF SO, WHAT STYLES?
- L/S/P American Lagers (from yeast character is optional)

HOW IS IT CAUSED?

• Premature removal from yeast
• Premature flocculation
• Oxygen depletion
• Bacterial spoilage
• Oxidation

HOW CAN IT BE AVOIDED/CONTROLLED?

• Allow ferment to complete
• Good yeast strain
• Aerate wort pre-pitching
• Practice good sanitation
• Beer handling to avoid O2 contact
• long lagering will reduce

Question 3

BJCP Description

Answer 3

This compound has the taste and aroma of fresh-cut green apples, and sometimes has notes of grass, green leaves or latex paint. It is normally reduced to ethanol by yeast during the secondary fermentation, but oxidation of the finished beer may reverse this process, converting ethanol to acetaldehyde. Elevated levels are generally present in green beer or if the beer is prematurely removed from the yeast. It can also be a product of bacterial spoilage by Zymomonas or Acetobacter. This flavor can also be the result of inadequate wort oxygenation, and while the resultant yeast by-products are normally metabolic intermediates, they can remain after fermentation in some cases. While acetaldehyde is normally considered to be a flaw, a low level is acceptable in the aroma and flavor of Kellerbiers, which typically have more yeast character than German beers that have been lagered.