We know that much of the good stuff – flavour, colour, tannin – in red wine comes from the skins. But fully ripening black grape tannins and colour can be a struggle in cool climates. Winemaking is always a balancing equation of extracting the most of the best stuff while leaving the less good stuff. It’s a different bit of algebra every year according to the growing conditions.
Pinot noir is the epitome of cool climate black cultivars. Using this grape variety Dr. Angela Sparrow at the University of Tasmania, Australia has come up with a new way to extract phenolics from the skins. Her work was presented to delegates at the International Cool Climate Wine Symposium in Brighton, UK, in May 2016.
Sparrow devised what is known as the ACE (accentuated cut edges) technique of pinot noir maceration. She said “there is relatively more seed tannin than skin tannin with pinot noir”, which is not so good. The skins are the best place from where to get tannins. “With grape skin fragments” she said “there is leakage from the broken edges. [Phenolics] fall out of the broken cells, rather than diffusing out via the pulp.”
Ergo, if you have a grape skin piece that’s 2cm x 2cm, that’s 8cm of edges. If you cut the original piece into four pieces, you have 4 pieces x 1cm square, or 4 pieces x 4cm of edges i.e. 16cm. And so it goes on.
The technique cuts only the skins, not the seeds – which would release the more bitter phenols contained in seeds. This secret bit of kit was not discussed!
There is a limit to the amount of cut edges required. Sparrow said “once you get to about ten bits from one [crushed bit], then you have much better extraction of colour and phenolics. It doesn’t make a huge difference if you go more pieces / smaller fragments. Five to ten bits is very good.” And smaller bits clog up the press.
The best time to apply the ACE technique was found to be day one, i.e. early after crushing.
Sparrow added that with ACE it is stable pigment that is released from the skins. “You don’t need to worry about browning of pinot noir colour later, which can happen when you have lots of seed tannin.”
Sensory evaluations after six months evaluated hue, colour density, aroma, palate, structure/texture, balance, length, tannin. The ACE wines typically scored higher than the control wines made conventionally.
Another type of pinot noir maceration – controlled phenolic extraction – has also been researched in Tasmania.