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Aroma: Butter or Butterscotch

Problem:

A beer with a buttery or butterscotch aroma indicates the presence of diacetyl. This substance is produced normally in beermaking and is then converted to 2,3 butanediol during a healthy fermentation.

Causes:

  • Excessive oxygen can degrade fermentation.
  • Bacterial contamination (Sarcina sickness or Pediococcus) that occurs at the end of wort fermentation can prevent diacetyl conversion.
  • Worts low in the amino acid valine do not promote the proper reduction of diacetyl by the yeast.
  • Premature wort cooling with the lack of a strong cold break can promote the presence of diacetyl.
  • A high pitching temperature can reduce the yeast effectiveness.
  • Worts with high amounts of sugars and starches can impede full fermentation.
  • Decreased flocculation and settling by weak yeast strains can prevent diacetyl conversion.
  • Blocked conversion of diacetyl can be caused by defective yeast.
  • A weak boil can result in excess diacetyl amounts being present.
  • Cooler temperatures at the end of fermentation help keep diacetyl present.
  • Some yeast strains are prone to diacetyl formation.
  • Incomplete fermentation or excessively warm temperatures.

Cures:

  • Conduct smooth transfers from vessel to vessel to prevent aeration of the beer once the yeast is pitched.
  • Do NOT re-pitch yeast.
  • Formulate recipes to provide yeast with all necessary nutrients, including amino acids.
  • Maintain a strong rolling boil for at least one hour, followed by a rapid cool-down of the wort to ensure a strong cold break.
  • Maintain sanitary conditions.
  • Pitch at lower temperatures appropriate for the yeast.
  • Prepare a yeast starter, especially for higher gravity worts, to ensure sufficient yeast is available at the time of pitching into the wort.
  • Use high-quality yeast in good condition.
  • Achieve a strong, rolling boil for at least one hour.
  • Add a 24-48 hour period of higher temperature fermentation at the end, called a diacetyl rest.
  • Use a neutral yeast strain that is not prone to producing diacetyl.
  • Allow time for full fermentation at proper temperatures.
Aroma: Butter or Butterscotch