Production of Whisky Using Specialty Malts: An Optimised Process
Academic Institution: Heriot-Watt University
Academic Supervisor: Dr Calum Holmes
Industry Partner: Holyrood Distillery / Crisp Malt
PhD Student: Rutele Marciulionyte
Start Date: 25th July 2019
Summary
Specialty malts are extensively used in the brewing industry, contributing to beer taste and aroma, mouthfeel, and colour. Such malts are produced under conditions of high temperature, which results in non-enzymatic browning and an increased concentration of aromatic constituents, primarily through the action of Maillard chemistry. The majority of Scotch malt whisky is made using lightly kilned malted barley that yields only delicate aromas to the finished product. The characteristics differentiating whisky of one distillery from another is primarily introduced by varied distillation and maturation practices. With demand increasing for greater whisky variety, attention is turning to the utilisation of specialty malts. However, currently available specialty malts are produced primarily for brewing, and there exists comparatively little information regarding the impact of their use in distillation.
The present study investigated the impact of grain roasting conditions on malt quality characteristics, fermentability, volatile composition of the distillate and its change during maturation. Samples of Pot Still Malt were roasted at laboratory scale (100 mL batches) following designed experimentation methodology and used to produce a new make spirit. Commercially available specialty malts were used to produce spirits at full industrial scale (600 L batches) at Holyrood distillery, afterwards the spirits were filled into ex-bourbon oak barrels for maturation. SPME/GC-MS analysis was used to evaluate the composition of malt volatiles, while a liquid-liquid extraction GC-MS, headspace GC-FID and HPLC methods were developed to analyse the congeners in distillate and maturing spirit.
The project highlights the importance of grain roasting with regards to the number and concentration of heat-derived flavour-active volatiles present in malt and their carry-over into distilled spirit. The findings of this study have considerable implications for the commercial use of roasted malts in whisky production, and for the production of roasted malts for the distilling industry.
Key Results/Outcomes:
· Malt roasting creates flavour volatiles (furans, pyrazines, pyrroles, pyridines) of coffee, chocolate, roasted nut aromas through Maillard and caramelisation reactions.
· Aroma volatiles from malt are carried to the spirit during whisky production process.
· Use of roasted malt has negative effect on alcohol yield, but it can be mitigated by using low roasted malt inclusion rates (10%) or roasting malt at lower temperature (up to 180°C).
· Roasted malts can impact yeast fermentation characteristics and yeast-produced aroma volatiles (esters and higher alcohols).
Publications:
Marčiulionytė, R., Johnston, C., Maskell, D. L., Mayo, J., Robertson, D., Griggs, D., & Holmes, C. P. (2022). Roasted Malt for Distilling: Impact on Malt Whisky New Make Spirit Production and Aroma Volatile Development. Journal of the American Society of Brewing Chemists, 1-12. https://doi.org/10.1080/03610470.2022.2034133
Awards:
Poster award at SRPe conference, 2022
Best PhD student prize (Heriot-Watt University, Institute of Biological Chemistry, Biophysics and Bioengineering), 2021
Conference posters:
Presented posters at SRPe conferences, 2019, 2021, 2022
Talks given at conferences:
Brewers Journal Congress, 2022
American Distilling Institute Conference, 2022
American Society of Brewing Chemists and Master Brewers Association of the Americas Brewing Summit, 2022
Worldwide Distilled Spirits Conference, 2021
Interview:
Interview for Distillers Journal, Issue 5, 2022
https://issuu.com/meatpacking/docs/dis_issue_5_digi?fr=sYWUzNTMwODY5MjU (Pages 54-57)