Skin contact - this is the amount of time that the skins of the grapes stay in contact with their juice! How long do they stay on for? Well it completely depends!
Perhaps the most significant factor: grape variety. Whereas most whites are separated straight away, most reds stay together for a prolonged period of time, and Rosé, well that can be just for a few hours. We’ll look at why this is a little later on, but for now, let’s look at the various types of skin contact:
This is when, before the grapes are mechanically pressed, the weight of their pile causes the grapes to split, resulting in juice (actually known as 'must') and skins separating. With white wines, this initial juice is considered to be the highest quality since it has the least amount of contact with bitter elements in the pips, skins and stems.
The name of the chemical process that happens when grape skins are touching a wine and releasing their phenolic materials (tannin, colour and flavour compounds) into the must. It’s a rising temperature that encourages the breakdown and extraction of the phenolic materials from the grape skins.
The thick layer of skins, stems and seeds that forms at the surface of fermenting red wine. Cap management, or breaking up the cap to increase contact between the skins and the liquid, is how the winemaker controls how long the must and skins maintain contact.
When thinking of skin contact, you have to also think about whole bunch.
After the grapes have been picked and sorted, it’s the winemaker’s choice (and often variety influence) as to whether it’s the whole bunch of grapes - with stems and all - that go into the tank/barrel for fermentation, or if all stems are removed and it’s only the berries that get fermented.
Typically red wine grapes with thinner skins and soft tannins - like Pinot Noir - keep their stems in order to add more tannin and phenolics into the must. Whereas thicker skinned grapes - like Cabernet Sauvignon - are often de-stemmed to reduce the chance of the wine becoming too bitter with harsh tannins.
White wines are typically not fermented with their skins and seeds attached to attain their lighter, fruity characteristics. However they can be, and that’s when the white grapes get a new name: Orange Wine. Orange winemaking is a natural process that usually uses little additives, if any at all. The process produces wines from white grape varieties that have a sour taste and a nuttiness that comes from oxidation. The practise of orange winemaking has been around for thousands of years, believed to have originated in the Caucasus region. It is still a popular technique used in Eastern Europe, whilst in the New World, it is gaining more and more popularity by the day. Australian winemakers are tending to use Sauvignon Blanc as the grape of choice - one of our favourites being BK Wines Skin n Bones White.
Craggy Range’s ex-chief winemaker, Matt Stafford, says that "stems lengthen the structure and give a savoury, rather than sweet, finish to the tannins". There’s also the view that using whole bunch actually increases the age-worthiness of the wine.
In terms of the actual science, using whole bunches of grapes means that a certain degree of carbonic maceration takes place at the beginning of the process. Made famous by Beaujolais, carbonic maceration involves intracellular fermentation within unbroken grapes, aka fermentation starts inside the grape.
At the beginning, the stem doesn’t have much impact as the ferment is taking place within the grape. However, after this intracellular stage they take on a more active role. Spread throughout a fermentation, the stems break up the mass of skins and pulp, affecting temperature and movement the oxygen and carbon dioxide gases.
The temperature of whole-bunch fermentations is thought to be more regular throughout the tank, because the liquid circulates more easily. This avoids the hotspots that can accumulate in de-stemmed fermentations. In fact, the overall temperature tends to be lower so the process of extracting tannin and colour is more gentle.
Stems also allow gases to move more freely. That means the escaping carbon dioxide doesn’t produce such a thick cap of skins, and it allows oxygen to permeate the fermentation to keep yeast active. However, it’s important to note that if there are too many stems in a tank, pumping over becomes impossible, which could actually reduce the oxygen in the ferment, hence 100% whole bunch fermentations are very rare. It’s more common to have a proportion of whole bunch combined with otherwise de-stemmed fruit.
Tim Kirk of Clonakilla, uses some whole bunch to make his Shiraz Viognier. The whole bunches are put into 2 ton fermenters, only part full. Some Viognier is typically crushed and de-stemmed and put on this, and then some Shiraz is de-stemmed and put on top. Kirk reports that about 20% of the grapes in the whole cluster portion stay attached to the rachis and don’t burst. Instead, they start to go through carbonic maceration.
This delayed sugar release from intact berries is also noted by Felton Road's Blair Walter, who uses a little bit of whole bunch to add complexity to his wines. ‘We typically put in a quarter whole bunch and de-stem the rest of the bunches. And then when we punch down we don't go to the bottom of the tank. After 28 days you can still pull out whole bunches. They have fermented inside [the intact berries] and there is still some sweetness that is pulled out.’ He thinks this remaining sweetness is important because it keeps fermentation ticking along for a while. ‘Burgundians typically chaptalise in six-to-eight small additions,’ claims Walter. ‘This results in a slightly stressed fermentation producing more glycerol. This changes the texture and adds some fruit sweetness. It surprises me that more people don’t use whole bunches.’
One of the most prominent considerations is fruit quality. Light, early drinking reds are usually made with shorter skin contact times (eg. 1 week) and can be made with lower quality grapes, whereas full-bodied reds intended for ageing are usually made with longer skin contact times (3 weeks) and require a riper, better quality fruit.
Whereas Beaujolais can certainly claim to be the spiritual home of whole-bunch fermentation, we’ve got some New World beauties from Australia and New Zealand for you to check out too!
Fine musky florals to white pepper, with an incredibly exuberant explosion of fruit, Ripe red cherry, raspberry and red plum flavour, chocolate and a dusting of white pepper.
Dark, earthy aromas with notes of soft rose & red berries. Intense fruit entwined with smooth tannins & fine acid.
Baked quinces and lavender custard with a sprinkle of dried marjoram and a slightly resinous edge. When you finally do get around to drinking, there is much craft to contemplate - beautifully scaffolded acidic freshness and chewy, chalky tannins.
Whole bunch with wild yeasts. Spicy and stalky, it has the customary black and red berry notes of Cabernet with a perfumed freshness and medium body. Fine-grained tannins are tempered by the influence of some carbonic maceration in the ferment.
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