Fizz whizzes

As a young Tasmanian agricultural science student, all Fiona Kerslake planned to do on graduating from university was to work in the field of animal production. She never imagined that in less than a decade she would become a Tasmanian Institute of Agriculture (TIA) Junior Research Fellow.

With a doctorate in viticulture and specialist skills and knowledge in cool climate wine production.

Times change, and so has the fabric of the wine industry in the former Apple Isle. Today, bottle-fermented sparkling wine is one of the great success stories of the wine industry there. Indeed, depending upon vintage, somewhere between 42% and 50% of all wine grapes grown in the island State now end up in bottles of premium fizz. 

"With that in mind, it's incredibly important that we continue to lead Australia's premium sparkling wine production and research," mused Jansz Tasmania winemaker Natalie Fryar as she welcomed the three dozen or so Tasmanian wine industry participants who gathered at Coal Valley Vineyard in late September 2013 to workshop sparkling wine viticulture.

The small southern Tasmanian vineyard on the outskirts of Hobart played host to a diverse range of industry players. All were united by mutual ambition and the desire to develop an understanding of the complexities – and indeed some of the mythologies – of growing cool climate Chardonnay and Pinot Noir to meet the specific requirements for high-end bottle-fermented sparkling wine.

Back in the 1990s, such an event would have hardly raised an eyebrow. At best, many Tasmanian growers and winemakers regarded sparkling wine as the logical end point for fruit that was surplus to table wine requirements. At worst, it was seen as a destination of last resort for high acid, under-ripe fruit in ultra cool seasons like 1996. Viticulturally, the differences hardly mattered. Vineyard management practices were largely based upon a 'one size fits all' approach.

"We can't just assume that applying the management practices used in table wine vineyards will provide us with the best way of managing sparkling wine production," Fryar noted in her opening address.

"We have to be prepared to go out and challenge some of those ideas. I think anyone who wants to produce a flagship sparkling wine has really got to go out and do that. I think I can say that just looking back over the past 14 years – the period of time I've been working with Tasmanian vineyards – the industry here has done incredibly well in meeting those challenges.

"Sparkling wine is fundamental to the business of the Tasmanian wine industry. And yet, it's a place where even growing fruit on the same site can change markedly from vintage to vintage. It's a place where you really need to have a very close relationship with the person who's going to be making your wine. Your role is all about being in the vineyard, day after day, tasting your fruit."

Sharing the role of workshop facilitator with Fryar and renowned Tasmanian wine pioneer Dr Andrew Pirie, Dr Kerslake pointed out the first vineyard component of the island's sparkling wine research project began in vintage 2009. She went on to outline the key role played by recently retired South Australian Dr Bob Dambergs. Dambergs was the Australian Wine Research Institute's man on the ground in Tasmania during the sparkling wine research program. Formally attached to TIA in Hobart, he was the institute's first senior research scientist to be based outside Adelaide.

Over the project's three-year period of Federal Government Ausindustry funding, Drs Dambergs and Kerslake vinified hundreds of 12kg ferments of Chardonnay and Pinot Noir samples. These were obtained at the end of carefully devised trials of common viticultural management practices carried out in dedicated sparkling wine vineyards located in northern and southern Tasmania.

Dr Dambergs subsequently went on to analyse the data obtained from the sparkling wine bases created from these project ferments. His skilful use of ultra-violet spectral measurement and principal component analysis enabled Dr Kerslake and Dr Joanna Jones – Research Fellow at the Tasmanian Institute of Agriculture – to identify the many distinct clusters of data that revealed significant effects on wine grape and sparkling wine quality.

With Dr Jones working at Tolpuddle Vineyard in southern Tasmania and Dr Kerslake based at Kayena Vineyard in northern Tasmania, the pair conducted a range of cane and spur-pruning trials during the growing seasons that led up to vintages 2010-2013.

Cane pruning is the predominant method for establishing vine architecture in Tasmania. However, its pre-eminence is generally compromised by additional cost factors and the greater level of skill required to perform it properly. Indeed, Dr Jones' pruning trials of Pinot Noir (clone D5V12) and Chardonnay (clone I10V1) over three seasons at Tolpuddle Vineyard confirmed the presence of pronounced apical dominance among the project's cane pruned vines. Careful canopy assessment of the property's Chardonnay vines provided additional data that revealed significant differences in canopy density between the two pruning regimes.

"Our overall results indicated that canopies established much more quickly and were denser and more even when vines were spur pruned," Dr Kerslake explained.

"Spur pruning also resulted in the production of many more smaller bunches without any significant differences in yield per vine. The only exception we found came from spur pruned Chardonnay vines in 2012, which favoured increased yields over cane pruning. Similarly, we found that while fruit quality parameters were not significantly different, the analyses of base wine spectral data showed that there were distinct separations between the two systems. This suggests that there may be detectable sensory effects in the base or finished wines.

"There are two qualifications needed here, however. One is that in 2010, when vines had just been converted to spur pruning, vines had significantly lower total grape phenolics. That effect appears to fade over time as there were no differences between established spur pruned and cane pruned vines. The second is that while we did some analyses of vine carbohydrate reserves and found spur pruned Pinot Noir vines had higher levels of overwintering carbohydrates in their canes in some years, the biggest differences noted were the differences between the seasons. In other words, all of the various seasonal effects were greater than the experimental effects."

At this point in the workshop's discussion program, Dr Pirie offered additional anecdotal evidence highlighting the potential critical outcomes of abnormal seasonal effects in Tasmania.

"I can recall that during my time at Tamar Ridge, we conducted various spur versus cane pruning trials," he said.

"For a fair number of years, it looked like the spur pruning guys were winning the economic battle because of the cost savings they were able to achieve. But then in 2012, there were very dramatic seasonal impacts, with certain clones of Pinot Noir producing almost no fruit on their spurs. Vintage 2012 just happened to follow 2011, which had a very difficult fertility season because of the weather influences that year.

"What subsequently happened was that those spur pruned vines then leapt into a big vigour cycle, and that's the real danger of going to spur pruning, especially in the wetter parts of the industry. Spur pruning might look alright for a while but then it can suddenly collapse and you've got major problems."

Dr Pirie went on to briefly affirm the merits of the cane pruned unilateral system he has established at his Apogee Vineyard at Lebrina in Tasmania's northeast. These Scott Henry trellised vines – which have shoots on their lower cordon trained downwards and those above trained upwards – are established with very effective ventilation windows between their two arms. That allows enhanced air movement and thus increased protection from botrytis bunch rot and powdery mildew. Spacings of about 30cm-40cm between successive canes also facilitate better sunlight penetration during the growing season. The net effect is alleviation of cane pruning's characteristic apical dominance. Bud initiation and bud fruitfulness are also significantly increased.

"That highlights another aspect of our Tamar Ridge experiences," Dr Pirie noted.

"We found we'd do all these cane and spur pruning trials – and we'd make some very significant cost savings on the latter – but come the end of the season and we'd often find we had botrytis issues. You'd then need to do a whole lot of expensive bunch-thinning that had never been factored into the cost analysis. 

"My feeling is that while cane pruning and Scott Henry trellising have much more of an upfront cost associated with them, the lack of botrytis you get in using them provides you with a payback at the end of the season. Spur pruning looks really cheap when you do it but you've got major problems with it in Tasmania when you get a wet season."

Last September's sparkling wine workshop ended on a high note with Dr Kerslake conducting a blind tasting of four samples of recently disgorged experimental sparkling wine. Made by Dr Kerslake herself during her research at Brown Brothers' Kayena Vineyard micro-winery in 2010 and 2011, they provided workshop participants with some impressive physical evidence of the value of the project team's crop load investigations.

The tasting's two highest pointed wines resulted from cane-pruned vines bearing the highest crop loads. In both cases, the vines were pruned to 60 nodes per vines – essentially, six canes bearing 10 nodes each. The tasting's clear favourite carried additional weight in its saddlebag. Its origins harked back to 2011 (a cool, wet year), having been made from Clone 114 Pinot Noir vines yielding at 18.4 tonnes per hectare. 

The wine perceived as the group's second highest pointed wine was created from the same clonal selection cropped at 13.3 tonnes per hectare in the warm, dry season of 2010. The two wines regarded as the tasting's least preferred samples were derived from 10 nodes per vine Pinot Noir cropped at 8.2 and 5.5 tonnes per hectare.

"Everything about the winemaking was standardised," explained Dr Kerslake, "and within each year, the fruit was harvested on the same day."

Of course, in the real world, high yielding Pinot Noir vines could never produce premium quality, bottle-fermented sparkling wine. Or could they?

Tasmanian sparkling wine quality now looks set to take another quantum leap forward if current and ongoing research is any portent of future success.

First published January/February 2014: Wine & Viticulture Journal, Vol 29, No 1