What actually happens when you add water to must?

11 Mar 2017
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The addition of water prior to fermentation is a legal and commonly used technique in a number of countries, including the United States, but surprisingly there has been little formal research into how the wine composition and sensory aspects are affected.

Food Standards Australia and New Zealand (FSANZ) recently announced a decision to allow the limited addition of water to high sugar musts and juice to reduce the chance of problems arising during fermentation.

Following this decision – and as soon as Shiraz grapes are available from the 2017 vintage – Paul Smith and colleagues at the Australian Wine Research Institute (AWRI) will be running a comprehensive range of trials involving 36 separate ferments, then bottling the wine and analysing it for a year before undertaking the all-important sensory evaluation.

The obvious question is what does changing the solid-to-liquid ratio by choosing to add water do to the complex web of extractions and chemical reactions that take place during fermentation.

‘Your first instinct is that you’ll dilute everything, but there is evidence from previous work that, for example, with tannins you don’t end up with a dilution because they are there in such excess that you’re really just providing more opportunities for them to be extracted out, so you more than compensate for the dilution,’ Dr Smith said.

The first part of the trial will be a straight dilution of high sugar juice with water. Dr Smith and AWRI colleagues Drs Keren Bindon, Paul Petrie and Bo Teng will take juice that comes in at around 15.5 Baumé and add water to bring it back to 14.5 and 13.5 Baumé – the latter being the new legal baseline. They’ll then measure tannins, polysaccharides and colour, flavour and aroma compounds in the resultant wine to gauge whether there has been any significant change.

A separate set of trials will test what happens if you dilute by replacing some of the crushed juice with an equal amount of water. The juice is diluted leading to lower alcohol, but the total volume and solid-to-liquid ratio don’t change.

And they’ll also see what happens with the traditional method of saignée, where you take some juice out and don’t replace it, thus increasing the solid-to-liquid ratio.

‘You might expect it to be more concentrated and it’s certainly the way people have approached it in the past, but we need to develop a body of evidence to show the effects’, Dr Smith said. ‘Theoretically, you can reach a saturation equilibrium where you can’t extract more; less wine but with the same alcohol concentration. We will find out for sure whether it concentrates the flavours or changes texture.’

In a related trial already under way, University of Adelaide PhD student Olaf Schelezki, working with Assoc. Prof David Jeffery and collaborating with AWRI, is testing the impact of replacing some juice with a ‘green harvest wine’ – essentially an acidic low alcohol wine made from grapes harvested at very low sugar levels, or with water. 

‘We want to look at obvious combinations of what you could do,’ Dr Smith said. ‘It will be the stepping point for people to better understand the impact of water addition to high sugar must, compared to the anecdotes.’

Dr Paul Smith

From a scientific perspective, it will add another piece to the puzzle that is understanding the complexities of the fermentation and extraction process.

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This content is restricted to wine exporters and levy-payers. Some reports are available for purchase to non-levy payers/exporters.