Cooked Onion (DMTS) Flavour Standard

What is Cooked Onion (DMTS) Flavour?
Cooked Onion flavour, also known as Dimethyl trisulfide (DMTS), is a sulphur-containing flavour that emerges during the brewing process. It is often described as:

• – Cooked onion
• – Garlic-like
• – Sulphurous or swampy

DMTS is naturally formed in beer during wort boiling and fermentation, originating from sulphur-containing amino acids or the oxidation of Methanethiol. Its detection threshold in beer is extremely low—around 40 ng/L—making it a subtle but significant flavour note for professional tasters.

What Causes Cooked Onion (Dimethyl Trisulphide) Off-Flavour?
The Cooked Onion off-flavour in beer is primarily caused by:

1. Brewing Process:

• – Formation of DMTS during wort boiling from sulphur-containing amino acids.
• – Oxidation of Methanethiol, another sulphur compound.

2. Fermentation:

• – While carbon dioxide typically purges DMTS during fermentation, residual amounts can remain, leading to the onion-like flavour.

3. Non-Alcoholic Beverages:

• – Contaminated source water containing decayed vegetation.
• – Decomposition of sugars and flavours in the final product.

Using the Cooked Onion Flavour Standard for Sensory Training
The Cooked Onion (DMTS) flavour standard is widely used in sensory training to help professionals:

• – Recognise the Flavour: Train beer tasters to identify the onion-like aroma and taste.
• – Scale Intensity: Develop the ability to measure the strength of the flavour in beer samples.
• – Improve Quality Control: Detect and address off-flavours during the brewing process to ensure product consistency.

How to Recognise Cooked Onion (Dimethyl Trisulphide) Flavour: Sensory Terms
When identifying the Cooked Onion flavour, tasters often describe it using the following sensory terms:

• – Dimethyl Trisulphide (DMTS)
• – Cooked Onion
• – Garlic
• – Swampy
• – Sulphurous

These descriptors help pinpoint the presence of DMTS and differentiate it from other sulphur-based flavours.

What are the Professional Applications of the Cooked Onion Flavour Standard?
The Cooked Onion Flavour Standard is widely used by:

• – Sensory panels and quality assurance teams to identify and scale the intensity of the onion-like flavour during sensory testing and quality control.
• – Breweries and beverage manufacturers use routine quality control to detect off-flavours caused by Dimethyl Trisulphide (DMTS) and ensure product consistency.
• – Sensory scientists and trainers for panel calibration, training, and proficiency testing, including In/Out schemes, to improve flavour recognition skills.
• – Research and development teams to study sulphur compounds, refine brewing techniques, and evaluate new formulations or processing changes.

It is also an essential component in sensory proficiency and benchmarking programs, helping organisations maintain consistent testing conditions and ensure that all samples are evaluated objectively against a standard reference for the Cooked Onion flavour.

Other Information
Beer Flavour Wheel Number: 0736

Typical concentration seen- 0.05 – 0.3 ug / l

The standard recommended by Peppard (J Inst Brew, 91, 364-369).