Low alcohol wines: blending with an early harvest or dealcoholisation of a later harvest?

Over the past 20 years the level of alcohol in wine has increased in most grapegrowing regions due to global warming and consumer preferences towards full-body, riper flavour wines. This has raised a number of issues related to consumer health including increased calorie intake and risk from alcohol-related illness and disease, tax policy interventions and wine sensorial quality. The adoption of low alcohol wines (broadly defined as containing 5.5-11%v/v alcohol) is one solution to addressing these challenges, thus still allowing the enjoyment of wine. Several methods have been implemented to reduce wine alcohol content, but removal of alcohol from wine at a post-fermentation stage (dealcoholisation) is the most accepted at the industrial scale (Schmidtke et al. 2012). Among the dealcoholisation processes, membrane-based technologies, such as reverse osmosis and evaporative perstraction (membrane contactor), are the most widely employed. However, these processes also cause significant losses of important volatile compounds such as esters, which are known to confer fruity aromas to wine (Longo et al. 2017). Aside from these chemical and sensory alterations, dealcoholisation requires a high capital outlay and may have poor eco-sustainability because of high energy inputs and water requirements (Margallo et al. 2015). A more attractive and ecosustainable approach would be to harvest grapes at an early stage of ripening, when they naturally contain lower concentrations of fermentable sugars. Unfortunately, insufficiently ripened fruit may not have adequate phenolic and aromatic profiles to produce consumer acceptable wines. Early harvested grapes tend to produce wines low in flavour intensity and higher in bitterness and herbaceous characters (Pineau et al. 2011, Bindon et al. 2013). Nevertheless, a wine made from early harvested grapes could be legitimately blended with wines obtained from later harvested grapes in order to produce a less alcoholic wine or fermented together, as shown more recently in a study by Schelezki et al. (2018a, 2018b).

A better understanding of how changes in aromatic compounds arise during dealcoholisation or blending processes, particularly fermentative by-products and grape-derived compounds, and how these changes impact the sensory profile of reduced alcohol wines is lacking. Research on the reduction of alcohol content has mainly focussed on small decreases in alcohol content (1-2%v/v), with minimal emphasis on understanding how chemical changes in wine affect sensory characteristics at greater alcohol reductions. As a part of a bigger project on lower alcohol wines conducted at the ARC Training Centre for Innovative Wine Production (Ristic et al. 2016), Rocco Longo established several trials to:

• evaluate wine blending as a tool to produce wines with more balanced, riper flavours and lower levels of alcohol
• assess the effect of dealcoholisation on the volatile composition and sensory profile of wines produced from mature fruit
• identify potential differences in the volatile and sensory composition of wines produced from early harvest regimes and dealcoholisation strategies
• understand how changes in chemical composition during alcohol reduction affects the sensory profile of wine.