WSET Diploma D1 Exercises (Specific Options for White Winemaking)

Answer

Skin contact means leaving crushed white grapes (or the juice with the skins) together for a period before fermentation, from around an hour to 24 hours or more (longer contact extracts more flavour and tannin). The juice is normally chilled (typically below 15°C), which slows extraction so it can be controlled, and reduces the risk of oxidation, spoilage organisms and a spontaneous fermentation.

Many aroma compounds and their precursors are found in or just under the skins, so skin contact increases the extraction of flavour and aroma precursors and, by extracting a small amount of tannin, can add texture. However, if it is overdone, the wine can taste bitter and feel coarse. It also slows processing and needs equipment and labour, so it is less likely to be used for inexpensive wines.

It suits aromatic varieties such as Riesling, Gewurztraminer, Viognier, Muscat and Sauvignon Blanc, where the aim is to maximise varietal aromas and, as these wines are seldom oaked, to add texture. Most white wines are made with little or no skin contact: it is avoided for delicate, pale, smooth wines, for wines to be drunk young (the tannins would not have time to soften) and when the grapes are not fully ripe (bitter, astringent compounds would be picked up).

Grading Criteria

• For stating that the skins are left in contact with the juice before fermentation, you get 1 point.
• For giving a typical duration (from about an hour to 24 hours or more), you get 1 point.
• For stating that it is carried out at a low temperature, you get 1 point.
• For explaining that chilling slows extraction or reduces the risk of oxidation/spoilage, you get 1 point.
• For explaining that it increases the extraction of aroma compounds or their precursors, you get 1 point.
• For stating that it can add texture or body, you get 1 point.
• For pointing out the risk of bitterness or coarseness if it is overdone, you get 1 point.
• For stating when it is avoided (delicate or early-drinking wines, underripe grapes), you get 1 point.
• For pointing out the extra time, equipment and labour (less likely for inexpensive wines), you get 1 point.
• For identifying aromatic varieties (e.g. Riesling, Gewurztraminer, Viognier, Muscat, Sauvignon Blanc) as benefiting the most, you get 1 point.

Answer

Hyperoxidation is the deliberate addition of oxygen to white grape juice before fermentation, without adding sulfur dioxide. The compounds that oxidise most readily (mainly phenolics) react first and turn the must brown, but they precipitate during fermentation, so the finished wine returns to its normal colour.

Advantages: the wine has fewer phenolics, so it is more resistant to browning (oxidation) later and needs less sulfur dioxide during its life; it can also remove bitter compounds that come from unripe skins, seeds and stems.

Disadvantages: some varietal aroma compounds (e.g. volatile thiols and methoxypyrazines in Sauvignon Blanc) can be destroyed, so the method suits less aromatic varieties such as Chardonnay better than aromatic ones; it is also an extra step that needs labour to set up and monitor, which adds a little to costs (the equipment itself is not particularly expensive).

Grading Criteria

• For stating that oxygen is deliberately added to the juice before fermentation, you get 1 point.
• For stating that no sulfur dioxide is added (so the juice is not protected), you get 1 point.
• For explaining that the most readily oxidised compounds (phenolics) oxidise and turn the must brown, you get 1 point.
• For explaining that the browned compounds precipitate during fermentation, you get 1 point.
• For explaining that the finished wine returns to its normal colour, you get 1 point.
• For stating that the wine is more resistant to later browning or oxidation, you get 1 point.
• For stating that less sulfur dioxide may be needed, you get 1 point.
• For stating that bitter compounds (e.g. from unripe skins, seeds and stems) are removed, you get 1 point.
• For pointing out the loss of varietal aromas (especially in aromatic varieties), you get 1 point.
• For pointing out another disadvantage (an extra step needing labour and monitoring, adding a little to costs), you get 1 point.

Answer

a) Sedimentation: the solids are left to fall by gravity, usually with the must chilled (to around 4°C) to slow oxidation and spoilage and avoid a spontaneous fermentation; the clear juice is then racked off. It is the cheapest and most traditional method, needing no extra equipment or additives, but it is slow (12–24 hours is not uncommon), ties up tank space, uses energy for chilling and is a labour-intensive batch process, so it is mostly used for small volumes of premium wine.

b) Flotation: a gas, usually an inert gas such as nitrogen, is bubbled up through the must; the solids rise with the bubbles and are skimmed off the top. Fining agents must be added to bind the particles together (if oxygen is used, it is also a form of hyperoxidation). It is quick and effective, can be continuous or batch, and the must does not need chilling, saving energy. However, it needs gases, fining agents and equipment, costs a little more than sedimentation, and can only be used on must, not wine.

c) Centrifugation: the juice is spun at high speed so that the solids are thrown out. It is very fast and works continuously, saving time and labour, and can be used on wine as well as must. However, the equipment is expensive, so it is mainly used by wineries that process large volumes; it exposes the must to oxygen unless it is flushed with inert gas (an extra cost), and it can over-clarify the must (very low solids can lead to a stuck fermentation).

d) Clarifying agents (e.g. pectolytic enzymes, bentonite): pectolytic enzymes break down pectins so the solids separate from the juice faster (they work on must only), and some fining agents help particles bind and settle. They speed up settling and save the time and energy of long, chilled sedimentation, but they cost money to buy, some can strip flavour or texture, and some fining agents are of animal origin (an issue for vegan labelling).

Grading Criteria

• For explaining how sedimentation works (settling by gravity, often chilled, then racking), you get 1 point.
• For an advantage of sedimentation (cheapest, simple, no equipment or additives), you get 1 point.
• For a disadvantage of sedimentation (slow, tank space, cooling energy, batch labour), you get 1 point.
• For explaining how flotation works (gas bubbles carry solids to the surface), you get 1 point.
• For an advantage of flotation (fast, continuous, no chilling needed), you get 1 point.
• For a disadvantage of flotation (fining agents, gases and equipment needed; must only, not wine), you get 1 point.
• For explaining how centrifugation works and an advantage (fast/effective), you get 1 point.
• For a disadvantage of centrifugation (cost, oxygen pick-up, over-clarification), you get 1 point.
• For explaining what clarifying agents do and an advantage, you get 1 point.
• For a disadvantage of clarifying agents (cost, stripping flavour, vegan issues), you get 1 point.

Answer

a) Pressing: grapes are often whole-bunch pressed gently, which gives clear juice with low levels of phenolics. Some producers deliberately keep a relatively high level of solids (around 1–2 per cent or a little more) in the must for texture and complexity, which needs careful monitoring to avoid reductive off-flavours.

b) Fermentation temperature: premium Chardonnay is often fermented at a relatively warm temperature for white wine (around 17–25°C, sometimes higher) rather than very cold, because the aim is texture and complexity rather than simple fruity (estery) aromas. The warmer temperature also promotes yeast health and avoids esters such as isoamyl acetate (banana).

c) Fermentation vessels: small oak barrels (e.g. 225 L barriques, sometimes new) are widely used. Barrel fermentation integrates oak flavours better than moving the wine into barrel after fermentation, gives a deeper colour and fuller body (the oxidative environment), increases contact with the lees and gives more blending options. However, the barrels are costly and monitoring many small vessels is labour intensive. Some producers use larger vessels, concrete or steel to keep the fruit more pure.

d) Lees stirring (bâtonnage): ageing on the lees gives more body and a softer, creamier texture and protects the wine from oxygen, and stirring increases the release of yeast-derived (bready, savoury) compounds. Stirring with a rod means opening the barrel, so it adds oxygen: this reduces the build-up of reductive sulfur compounds but can also decrease fruity flavours. Rolling racks allow the lees to be mixed without opening the barrel. Stirring many barrels is labour intensive.

Grading Criteria

• For stating that whole-bunch or gentle pressing is common, you get 1 point.
• For explaining that this reduces phenolics or gives clear juice (or that some solids may be kept for complexity), you get 1 point.
• For stating that fermentation temperatures are relatively warm for a white wine, you get 1 point.
• For explaining that the aim is complexity or texture rather than fruity ester aromas, you get 1 point.
• For stating that fermentation in oak barrels is common, you get 1 point.
• For explaining that barrel fermentation integrates oak flavours better, you get 1 point.
• For another point about vessels (size, proportion of new oak, alternatives such as concrete/steel), you get 1 point.
• For stating that lees stirring adds body or a creamy texture, you get 1 point.
• For stating that it adds autolytic (bready, savoury) flavours, you get 1 point.
• For a further point on lees stirring (oxygen pick-up reduces reductive sulfur compounds but can reduce fruit; labour cost), you get 1 point.

Answer

a) Drying on the vine: grapes are left on the vine long after normal ripeness so they shrivel and water evaporates, concentrating sugar (e.g. Vendanges Tardives from Alsace, Spätlese). A dry autumn is needed to avoid grey rot, and yield falls. In a variant, the cane is cut shortly before harvest so the grapes shrivel faster (e.g. Jurançon).

b) Drying off the vine: picked grapes are dried on mats or racks, in lofts or in the sun (e.g. Recioto della Valpolicella, Vin Santo, PX). Drying in a controlled place reduces weather risk, but it is labour-intensive and needs space.

c) Noble rot: Botrytis cinerea infects ripe, healthy grapes in a climate with humid, misty mornings followed by dry, sunny afternoons. The fungus makes tiny holes in the skin so water evaporates, concentrating sugar and acid and adding flavours such as honey and marmalade. Several passes (tries) through the vineyard are often needed (e.g. Sauternes, Tokaji Aszú).

d) Freezing on the vine: grapes are picked and pressed while frozen (e.g. Canadian Icewine grapes must be picked at −8°C or below). Much of the water stays behind as ice, so only a small amount of very sweet, concentrated juice is obtained, with high acidity.

e) Stopping fermentation: fermentation is stopped before all the sugar is used up, most commonly by chilling (below 10°C) and/or adding a high dose of sulfur dioxide, then racking and sterile filtering so that fermentation cannot restart; adding spirit (fortification) is another option. The winemaker controls the balance of sugar and alcohol, and the method is quick and low-risk.

f) Blending in a sweetening component: a sweetening component such as unfermented grape juice (Süssreserve) or rectified concentrated grape must (RCGM) is added to a dry wine, usually just before bottling (sugar is not permitted in the EU). This gives precise control over the final sweetness and is cheap, so it suits high volumes of inexpensive wine.

Grading Criteria

• For explaining drying on the vine (late harvest; water loss concentrates sugar), you get 1 point.
• For explaining drying off the vine (picked grapes dried on mats/racks/in lofts), you get 1 point.
• For naming Botrytis cinerea and the conditions it needs (humid mornings, dry afternoons), you get 1 point.
• For explaining how noble rot concentrates sugar (and acid) and adds flavours, you get 1 point.
• For explaining that grapes are pressed while frozen and water is left behind as ice, you get 1 point.
• For a specific point on frozen grapes (temperature, small yield, high acidity, icewine/Eiswein), you get 1 point.
• For explaining that fermentation is stopped before all the sugar is fermented, you get 1 point.
• For giving methods of stopping fermentation (chilling, SO2, sterile filtration, adding spirit), you get 1 point.
• For explaining the addition of a sweetening component (unfermented grape juice / RCGM), you get 1 point.
• For giving a relevant example (e.g. Süssreserve, Sauternes, Recioto, Tokaji) or a cost/risk point, you get 1 point.