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This article originally appeared in the November 2017 edition of Grapegrower & Winemaker.

 

In this second instalment of a two part series, Paul Le Lacheur looks at an inventive technological breakthrough that’s transformed the process of making quality wine. Read part one of Fermenting success on page 53 of the October Grapegrower & Winemaker.


Undoubtedly there have been plenty of successes in lower intervention techniques like utilising skin contact and processing whole bunch. However, the tech sector has some equally exciting advancements to experiment with.

Advancing on the woes of trial and error, a recent technological improvement has introduced a new way of managing phenolics. The technique is called Controlled Phenolic Release (CPR) or ‘microwave maceration’.

Not to be confused with the cardio-pulmonary resuscitation of humans, CPR combines the pre-fermentation maceration of fruit with microwave heating. This is also different to thermovinification, which will be clarified later in the article.

Warmed up grape juice

The juice is first heated to 70 degrees Celsius, which is followed by a hold time. The hold time can be varied depending on the desired outcome.

Variable hold time in CPR allows winemakers to ‘dial in’ the desired phenolic diffusion rate, dictating the colour and tannin levels for any particular style. A longer CPR hold time equates to commensurately higher phenolic levels.

“70 degrees is the threshold temperature. At this temperature, biological membranes break down, loosen and become more porous,” said wine researcher at the Tasmanian Institute of Agriculture, Anna Carew. At the time, Carew had been working on a project, in partnership with the Australian Wine Research Institute on microwave heating for maceration.

When the biological membranes break down, phenolics are gently extracted from grape cells which diffuse into the surrounding juice.

“70 degrees is the threshold temperature. At this temperature, biological membranes break down, loosen and become more porous.”

 

CPR can greatly reduce and better control traditional maceration periods. Instead of a cold soak for up to one month, a CPR ‘warm’ soak may take just a week.

In a compressed vintage where everything ripens at once, colour may be a premium. Tank space may also be at a premium. This all creates the need for a quicker, safer maceration, which is where CPR has found its place.

The microwave technology can offer new options to winemakers, especially for reds. Techniques such as pressing off colour and tannin prior to fermenting are now achievable with the CPR technique, this means room for new experimentation.

‘Controlled damage’

When compared to crushing, using intra cellular enzymes to break down cells, or steeping must in the alcohol from fermentation, CPR is considered ‘controlled damage’, which offers a greater deal of malleability to the winemaker.

CPR also sanitises the must, sterilising any background yeast and bacteria. This means winemakers can be confident the strain of yeast culture selected is not in competition. The process can operate without interference to yeast-mediated aroma compounds, which may produce desirable fruity or floral characters.

Carew explained that CPR is different from thermovinification.

“Microwaving is a penetrative form of heating. It goes into cells and heats at a cellular and molecular level,” she said.

“Conductive heating [such as thermovinification] has to transfer all the way in from the outside part of the cell. [Therefore,] CPR is more effective for disrupting cellular structure.

“Conductive heating [such as thermovinification] has to transfer all the way in from the outside part of the cell. [Therefore,] CPR is more effective for disrupting cellular structure.

 

“There is significant difference in the amount of disruption of cellular components that hold onto phenolic contents, compared to standard conductive heating.”

Signature aromas high

Some wineries in Victoria’s Yarra Valley and Mornington Peninsula have signed up to commercial trial through Carew’s research, with compelling results.

Large differences were noted between two batches of Pinot Noir that were treated with the microwave maceration, when compared to a control.

One batch had been fermented with skins on, and the other with juice only. The juice only treatment yielded some notable results when it came to aromatics.

As Carew was pleased to note, 14 of the 16 aroma compounds examined by gas chromatography were significantly higher in the juice only treatment. Levels of signature aromas such as ethyl octanoate (red cherry) and ethyl decanoate (chocolate, black cherry) were also noticeably high.

Carew said the trials indicate this method is producing wine with good mouthfeel quality and decent length.

Please note: in the period between writing and publishing this article, Dr Anna Carew had left her role at the University of Tasmania and has since taken up a position with the Tasmanian State Government.

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