Fundamentals of whiskey flavour

Granted EU geographical indicator status in 2016, Irish Whiskey is an increasingly sought-after product globally. To help safeguard its status, researchers at Teagasc & Technological University Dublin are seeking to map its unique properties.

Ireland is the birthplace of whiskey. Records date back to 1405, although it is thought that Irish monks learned the art of distilling from the Moors of Spain as far back as the 11th century. Whiskey – or whisky – is mainly produced in Ireland, Scotland, USA and Japan, but, also in Canada, India and a host of European countries on a smaller scale.

Whiskey production peaked in Ireland in the 1800s with an estimated 88 distilleries in operation. However, only two distilleries were active on the Island of Ireland by 1975; Irish Distillers in Midleton, Co. Cork, and Bushmills Distillery in Bushmills, Co. Antrim. Apart from the establishment of the Cooley Distillery in Co. Louth in 1987, very little growth occurred in the sector until 2010. Today, however, there are over 40 distilleries in operation in Ireland. Most of these new operations are craft distilleries but some are relatively large-scale operations. The growth in Irish whiskey has been rapid as the value of exports increased from ~€200 million in 2010 to over €1 billion in 2022. A number of factors are responsible for this growth, such as better marketing, but also the ability to produce a more flexible or diverse range of products than some competitors.

The main export markets for Irish whiskey are the USA (42%) and the EU (22%). Irish whiskey is subdivided into four main types; Irish Malt Whiskey, Irish Pot Still Whiskey, Irish Grain Whiskey and Irish Blended Whiskey, which is made by blending Grain whiskey with Malt whiskey and or Pot Still whiskey. Irish Blended Whiskey is by far the largest category making up over 90% of all sales.

A unique blend

“Irish whiskey received geographical indicator (GI) status within the EU in 2016, which not only provides assurance of quality and tradition, but also offers a level of protection against fraud,” explains Principal Research Officer for Teagasc Kieran Kilcawley. “For Irish whiskey to be recognised as both a spirit drink and of Irish origin, it must comply with certain legal definitions, under EU Regulations EU 2019/787 and 2021/1235 and the Irish Whiskey Technical File. In addition, Irish whiskey must be produced as well as matured on the island of Ireland.”

Whiskey production can appear as a relatively fundamental process; cereal (barley, wheat, rye, maize, etc), malting, kilning, mashing, fermentation, distillation, maturation and blending. However, as Kieran points out, minor alterations in the process can have a significant impact on the sensory characteristics of the final product.

“There are several unique aspects to Irish whiskey production,” he explains. “These relate to the ability to utilise exogenous enzymes to enhance the conversion of starch into fermentable sugars, the use of wood other than just oak in the maturation process, and the relative uniqueness of Pot Still whiskey. In Pot Still whiskey the mash bill consists of a minimum of 30% malted barley, a minimum of 30% green (unmalted) barley and 5% other cereals. This is distilled in copper pot stills resulting in flavour profiles that differ from those achievable from a single cereal source.”

The compounds responsible for the flavour of whiskey are known as congeners. These consist of a wide range of volatile, semi-volatile and non-volatile components, resulting from raw materials (cereals), or from one or more stages in the whiskey production process, with fermentation and maturation generally assumed to have the greatest impact.

On the nose

Teagasc, in partnership with the Technological University of Dublin, initiated in 2022 the project ‘Identification of Biomarkers to Authenticate Irish Whiskey and to Safeguard against Fraudulent Practices’.

The aim of this project is twofold, says Kieran: “We aim to create a database of key congeners in Irish whiskey that could be used to authenticate the different types of Irish whiskey, and also to enhance our understanding of the evolution and impact of these congeners in relation to sensory quality.”

Flavour is predominately a combination of taste and aroma, with aroma having a significantly greater impact as it can be perceived both orthonasally (through the nose) and retronasally (from the mouth). In fact, more than 10,000 aroma compounds are known to exist as opposed to a minority of taste compounds.

Kieran explains that the first major step in the project was to develop a robust method to identify volatile aroma congeners in whiskey using gas chromatography mass spectrometry expertise and capability within the Flavour Chemistry facility at the Teagasc Food Research Centre in Moorepark, Co. Cork.

“We utilised state of the art techniques, such as solid phase micro-extraction ARROW, and two-dimensional chromatography with time of flight mass spectrometry to achieve unsurpassed detection of volatile congeners in both new make spirit and mature whiskey,” Kieran explains.

A novel method was developed that can identify more than 200 individual volatile congeners. This was recently presented at the Worldwide Distilled Spirits Conference in Edinburgh, Scotland, organised by the Institute of Brewing and Distilling. This method is currently being used to generate a database of volatile congeners in new make and mature Irish Malt and Pot Still whiskey and subsequently in Grain and Blended Irish whiskey and in comparison to international products. 

‘Sources of volatile aromatic congeners in whiskey’, a review by Teagasc’s Kieran Kilcawley and Thomas Kelly and Technical University of Dublin’s Christine O’Connor, has been published online in the journal MDPI Beverages. You can read it at mdpi.com/2306-5710/9/3/64.

“More than 10,000 aroma compounds are known to exist, as opposed to a minority of taste compounds”

€1 billion: The export value of Irish whiskey has grown from €200 million in 2010 to over €1 billion in 2022

Acknowledgements

We would like to thank the Irish Whiskey Association, the Department of Agriculture Food and the Marine, the State Laboratory, the Food Safety Authority of Ireland, Science Foundation Ireland and the whiskey producers who have supplied product.

Funding

Funded by Teagasc Project 1376 Identification of Biomarkers to Authenticate Irish Whiskey and to Safeguard against Fraudulent Practices.

Contributors

Kieran Kilcawley, Principal Research Officer, Teagasc Food Research Centre, Moorepark. kieran.kilcawley@teagasc.ie

David Mannion, Food Chemistry Technologist, Teagasc Food Research Centre, Moorepark.

Thomas Kelly, Teagasc Walsh Scholar, Teagasc Food Research Centre, Moorepark.

Christine O’Connor, Head, Environmental Health and Safety Management, School of Food Science and Environmental Health, Technical University of Dublin.

Further Information 

Read this published research paper from the team: 

Sources of Volatile Aromatic Congeners in Whiskey

[pic credit] Smit / shutterstock.com