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Aroma: Butter or Butterscotch
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.
- 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.
- 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.