Removal of Unwanted Volatile Flavour Compounds Flashcards
(22 cards)
What undesirable compound is of particular concern for lager beers during wort boiling?
Dimethyl sulphide (DMS)
DMS has a canned sweetcorn aroma.
How is dimethyl sulphide (DMS) produced?
By thermal decomposition of S-methyl-methionine (SMM)
What is the typical maximum level of SMM or DMS precursor (DMSp) supplied to the brewery?
5 mg/kg
What is the boiling point of DMS?
38°C
How does increasing the wort boiling temperature from 100°C to 110°C affect the conversion of SMM to DMS?
Reduces the conversion time from 70 min to 22 min
What is the impact of pH on the conversion of SMM to DMS?
Higher pH promotes conversion; at pH 5.2 it takes 38 minutes to convert half the SMM, while at pH 5.5 it takes 32.5 minutes.
What happens to DMS after the wort enters the clarification vessel?
Any DMS formed is not evaporated and may lead to a cooked sweetcorn smell.
What is the flavour threshold of DMS?
About 30-50 μg/L
What is the typical total DMS specification for wort at the end of boiling?
Below 50 µg/L
True or False: Most brewers measure total DMS towards the end of the boil.
False
What is another precursor to DMS found in malt?
Dimethyl sulphoxide (DMSO)
What conditions can lead to DMSO being converted to DMS during fermentation?
Warmer fermentations
List some methods to prevent excessive levels of DMS in beer.
- Malt with low SMM levels
- Lower pH during fermentation
- Sufficient heat to convert SMM to DMS
- Effective evaporation and removal of volatiles
- Short wort clarification residence time
- Rapid wort cooling
- Wort stripping after clarification
What is isobutyraldehyde known for in beer production?
It can give beer a grainy flavour.
What does the presence of elevated levels of 3-methylbutanal in wort indicate?
Volatile removal was not effective.
What must be collected from the inside of the wort kettle stack to prevent backflow?
Condensate
What two methods can be used to evaluate the condensate produced during boiling?
- Analyze for flavour compounds using GCMS
- Physically check its odour
How does a higher pH affect the Maillard reaction during wort boiling?
Produces more DMS and more colour and flavour
What is thermal load in the context of wort boiling?
The total amount of heat applied to the wort
What is 2-furfural and why is it significant in measuring thermal load?
A Maillard reaction product with low volatility; lower thermal load produces lower levels of 2-furfural.
What is the thiobarbituric acid index (TBI) used for?
To measure thermal load based on the reaction with heat-derived organic compounds
True or False: A long boil at a specific temperature imparts a lower thermal load than a shorter boil at that temperature.
False
