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, usually for a few hours up to about a day. It is normally done at a low temperature to limit the extraction of tannins and the risk of oxidation and microbial spoilage.

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 can add texture. However, it also extracts phenolics, which can give bitterness, a coarser texture and a deeper colour that browns more easily, and it can raise pH because potassium is extracted.

It suits aromatic varieties such as Muscat, Gewurztraminer, Sauvignon Blanc and Riesling, where the aim is to maximise varietal aromas, and some fuller white wines. It is avoided for wines where delicacy and freshness matter, such as base wines for traditional method sparkling wine.

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 (hours up to about 24 hours), you get 1 point.
• For stating that it is carried out at a low temperature, you get 1 point.
• For explaining that a low temperature limits phenolic extraction or 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 from extracted phenolics, you get 1 point.
• For pointing out deeper colour or a greater risk of browning, you get 1 point.
• For pointing out that pH can rise because potassium is extracted, you get 1 point.
• For identifying aromatic varieties (e.g. Muscat, Gewurztraminer, 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 oxygen lets enzymes oxidise the phenolic compounds in the juice, which turn brown and drop out as a sediment (or are removed by clarification). During fermentation, the yeast reduces the remaining browned compounds, so the finished wine is pale again.

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 reduce bitterness and give a softer texture.

Disadvantages: some varietal aroma compounds (e.g. thiols in Sauvignon Blanc) can be lost, so the method suits neutral varieties better than aromatic ones; it can also reduce the wine’s ageing potential and needs additional equipment and care.

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 phenolics are oxidised and turn brown, you get 1 point.
• For explaining that the browned compounds precipitate and are removed, you get 1 point.
• For explaining that the colour of the finished wine becomes pale again during fermentation, 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 bitterness or harshness is reduced, 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 (e.g. reduced ageing potential or extra cost/equipment), you get 1 point.

Answer

a) Sedimentation: the juice is left to settle in a tank, usually chilled, and the clear juice is racked off the solids. It is simple and cheap and gentle on the juice, but it is slow (often 12–24 hours or more), needs tank space and cooling, and gives a lot of lees.

b) Flotation: a gas (nitrogen, or air/oxygen) is bubbled through the juice, often with a fining agent, so the solids stick to the bubbles and float to the top where they are removed. It is fast and continuous, suitable for large volumes, but it needs specialised equipment and some skill to operate.

c) Centrifugation: the juice is spun at high speed so that the solids are thrown out. It is very fast and effective, but the equipment is expensive, and it can over-clarify the juice or expose it to oxygen and heat if it is not well controlled.

d) Clarifying agents (e.g. bentonite, gelatine, pectolytic enzymes): they help particles to bind and settle or break down pectins. They speed up settling and can remove specific unwanted compounds, but they can strip some flavour or texture, some are of animal origin (an issue for vegan labelling), and they still need to be removed.

Grading Criteria

• For explaining how sedimentation works (settling, often chilled, then racking), you get 1 point.
• For an advantage of sedimentation (cheap, simple or gentle), you get 1 point.
• For a disadvantage of sedimentation (slow, tank space, cooling energy), 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, large volumes), you get 1 point.
• For a disadvantage of flotation (equipment or expertise needed), you get 1 point.
• For explaining how centrifugation works and an advantage (fast/effective), you get 1 point.
• For a disadvantage of centrifugation (cost, over-clarification, oxygen or heat pick-up), you get 1 point.
• For explaining what clarifying agents do and an advantage, you get 1 point.
• For a disadvantage of clarifying agents (stripping flavour, allergen/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 allow some solids (cloudier juice) into fermentation to add complexity.

b) Fermentation temperature: premium Chardonnay is often fermented at a relatively warm temperature for white wine (around 15–20°C or higher in barrel) rather than very cold, because the aim is texture and complexity rather than simple fruity (estery) aromas.

c) Fermentation vessels: oak barrels (often 225–228 L, a proportion new) are widely used. Barrel fermentation integrates oak flavours better than adding the wine to the barrel after fermentation, and the small volume makes temperature control easier. Some producers use larger vessels, concrete or steel to keep the fruit pure.

d) Lees stirring (bâtonnage): stirring the fine lees after fermentation adds body and a creamy texture, can add savoury, bready (autolytic) flavours and helps protect the wine from oxidation. Too much stirring can mask the fruit and make the wine heavy, so it is used with care.

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 (protection from oxidation, or risk of masking fruit), 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. late-harvest Jurançon). A warm, dry autumn is needed, and yield falls.

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. −7°C or below for icewine/Eiswein). 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, for example by chilling, adding sulfur dioxide, filtering or centrifuging out the yeast, or by adding spirit (fortification).

f) Blending in a sweetening component: a sweet component such as unfermented grape juice or concentrated grape must (e.g. Süssreserve in Germany) is added to a dry wine; this gives precise control over the final sweetness.

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, filtration/centrifugation, adding spirit), you get 1 point.
• For explaining the addition of a sweetening component (grape juice / concentrated must), you get 1 point.
• For giving a relevant example (e.g. Süssreserve, Sauternes, Recioto, Tokaji) or a cost/risk point, you get 1 point.