An Alternative to Cold Stabilisation
Tessa Nicholson Wine Press September 2010
Removing tartrate crystals from wine prior to bottling has become a vital link in the production. The most accepted way of doing so has been to cold stabilise down to minus 3 or 4 degrees, for a period of seven to 10 days. A long and costly expense. But now there is an alternative.
Tartrate crystals do not affect the wine in any way, other than cosmetically. There is no evidence that what are referred to as “wine diamonds” impact on flavour, aroma or clarity. But they are a turn off for the consumer, who may think the crystals are glass segments, or a sign of a bad batch.
Hence the need for their removal. Up until recently, the only way to remove the crystals was to add cream of tartar to the wine in tank, then lower the temperature to minus 3 or 4 degrees, for up to 10 days. The cold would lead to the tartrate forming into crystals on the sides of the tank, after which the wine is racked off, prior to filtering and bottling.
STARS (Selective Tartrate Removal System) is an electrodialysis (ED) process that has been developed by the French. Available in New Zealand for the past four years, the system is proving extremely popular in Marlborough, not only because it cuts power costs significantly, but it also speeds up the process for the winery that wants to get their wine out onto the shelf as soon as possible.
Roydon Allen from Vintech Pacific manages the mobile unit, which is based in Hawkes Bay. In Marlborough recently, he said the electrodialysis system is based on positive negative charges. Wine is pumped through two membranes which are selectively permeable, one to tartrate species and the other to potassium and calcium.
“I control how much charge I am putting through the machine, based on how stable I want to the wine to be. As the wine is fed through, the electrodialysis actually pulls the calcium and bi tartrates into a water stream, removing them from the wine, and flushing it out. It is a continuous process.”
“With ED we guarantee the wine at minus 4 degrees for six days – that is the EU standard.”
The portable machine can handle 6000 litres an hour, or up to 70,000 litres over a 12 hour period. Comparing that with having to cold stabilise for days on end, it’s easy to see why the French industry has moved to ED in the past decade.
But what does it mean for the winery? Clive Jones from Nautilus Estate says they have been using STARS for the past few years, and not because of the power cost saving measures it obviously provides.
“Our initial motivation was for calcium stability. We are a bit concerned about that, we have a tight calcium spec, as we find that most young Sauvignon Blanc tends to be calcium unstable when we test them.”
The issue with calcium is it generally takes a lot longer to show up in the form of crystals, than Potassium tartrates, which can occur quite quickly. Cold stabilisation for 10 days is all that is required to form potassium tartrates, but Clive says with calcium it can be six months after the cold stabilisation before the crystals form.
“We have been concerned about sending wines to the Northern Hemisphere where they could get exposed to cold temperatures and then develop calcium crystals. STARS certainly tidies that up, as it removes the calcium as well as the potassium.”
There are other motivating forces behind using STARS. Clive says because there is no need to cold stabilise, they are able to filter the wine at a cellar temperature of 10 degrees, instead of zero.
“When the wine is really cold, it is more viscous. Whereas when it is at room temperature the filter behaves better, we get much more efficiency out of it. We use a cross flow filter so we can filter at a higher flow rates when we are STARsing, meaning it takes a shorter period of time, there is less power used and washing cycles are minimised as well.”
Reducing losses is another reason for Nautilus to move away from cold stabilisation of Sauvignon Blanc. Racking off the cream of tartar before cold stabilisation means some wine is left behind. Rough estimates are that moving to STARS has seen losses drop from 2.5% to 1.0% .
“I can’t say the figures are absolutely accurate, but even if we reduce our losses by say 1.%, that is still significant. At say 90,000 litres that is a saving of 900 litres and even at say $3 a litre that has a value $2700.”
There are other advantages of the system Clive says, especially when it comes to Pinot Noir and pH levels. Winemakers often have to battle against high pH, which if left unadjusted can lead to colour loss in the ensuing wines. As STARS tends to drop pH levels during the electrodialysis process, it saves the winemaker a considerable amount of extra work.
“I am more and more convinced that cold stabilisation of Pinot Noir just wrecks it. It is hugely detrimental especially to the colour of the wine. So by STARS stabilising you can avoid chilling the wine, filter at cellar temperature and the reduced pH helps brighten it up. It is better for the wine, because it is a much softer filtration process. I can’t understand why everyone’s not doing it – particularly for those mid range commercial Pinots.
It is better for the wine, because it is a much softer filtration process. I can’t understand why everyone’s not doing it – particularly for those mid range commercial Pinots."
– Clive Jones, Nautilus Estate.