Floor Malting vs Drum Malting

The principal ingredient of whisky is grain, and to be more precise, malted grain. The malting process is essential before the yeast can start fermentation and produce alcohol. The process of malting is relatively simple. Firstly the grains are soaked in water and then kept warm until they germinate. Finally the germinated grains are heated to stop the germination process at the point where they are optimal for fermentation. The process might be simple but the changes that take place in the grain are complex, including both biochemical and structural transformations. Enzymes break down the grain's internal structure to make starches, proteins, and other compounds accessible. Other enzymes are produced that are available to convert starches to fermentable sugars and breakdown proteins to amino acids. With such complex changes it is not surprising that the method of malting has a significant affect on the malted grain, and the subsequent whisky. 

Floor malting is the traditional method of malting grain. Grains are soaked in water for 2-3 days and then spread on floors. The grain is turned every 6-8 hours to prevent root matting and to dissipate the heat. Windows are opened on warm days and fires are lit when its cold. When the germination phase is complete the grains are dried over 24-48hrs in a kiln. Floor malting is a manual process with little machinery or automation. The alternate method is drum malting, which is more modern, less manual and much more automated. Grains are steeped in automated tanks that cycle water and air. Grains are loaded into rotating drums and conditioned air is passed through the grains to encourage germination. Kilning may even happen in the same vessel (GKVs). As would be expected, the two methods produce malts that are very different. and these differences affect the flavour and mouthfeel of the whisky they are used to produce. Why this happens is due to the physical, chemical and microbiological difference in the malts. 

Physical differences arise because grains may be broken or crushed during the malting process. Drum malting can easily fracture the grain but floor malting is a much gentler process and much more grain remains intact. Kilning whole grain, rather than broken or crushed grain, preserves lipids and proteins in the malt and this contributes to a creamy texture and thick mouth feel. 

Chemical differences arise due to differences in grain modification. Drum maltings are optimised for yield and produce a malt with consistent modification throughout. Floor malting, on the other hand, introduces a degree of variability in the modification of the grain. Under -modified grain reserves β-glucans and proteins in the malt which contributes to viscosity, oiliness, and flavour complexity in whisky.

Microbiological differences arise because drum are sterilised whereas floors are not. The sterile environment of the malting drum limits microbial growth, where as the natural air flows in the floor malting house encourages controlled microbial activity, particularly lactobacillus. During fermentation the bacteria, notably lactobacillus produce esters such as ethyl lactate which again contribute to a silky, oily mouthfeel in addition to adding to flavour complexity. 

When all these differences are considered together it is clear that floor malted barley can produce a whisky with a more complex flavour and a thicker, oilier mouthfeel than drum malted barley. The disadvantage of using floor malted barley is the increased cost and the lower yields compared to drum malting. As a compromise, it is quite common for distilleries to use a combination floor malted barley and drum malted barley in their mash bills. However, a number of whisky distilleries use exclusively floor malted barley. A number of the casks listed on Still In Cask are also made exclusively from floor malted barley, notably the casks from Circumstance Distillery, Retribution Distillery and Abingdon Distillery all of which uses floor malted grain exclusively.