Clarification of Must Flashcards
Explain Centrifugation
A centrifuge is a machine that uses centrifugal force to separate solids from liquids. The advantage of centrifuges is that they clarify the must quickly. However, they are expensive to buy, therefore are typically only used in wineries needing to process large volumes of must quickly. They also increase the must’s exposure to oxygen unless the machine is flushed with inert gas, but that has an implication on costs
Explain Pectolytic Enzymes
Pectolytic enzymes break down pectins in the must. Breaking down the pectins allows a more rapid separation between the liquid juice and solids. Pectolytic enzymes only aid the clarification of must, not wine.
Explain Sedimentation
Sometimes called ‘settling’. The suspended solids in the must are left to fall over time with gravity. The must is commonly chilled to around 4°C (39°F) to reduce the rate of oxidation and microbial spoilage, and to avoid a spontaneous fermentation. The rate of sedimentation will depend on the size and shape of the vessel; it takes longer in large, tall vessels than in smaller, shorter vessels due to the depth over which the solids need to fall. Typically 12–24 hours. The clear juice is transferred to the fermentation vessel, leaving the sediment of solids at the bottom of the sedimentation vessel (a process called racking).
It can be used to clarify wines as well as must. Sedimentation is the cheapest method in terms of equipment required and is the most traditional way to clarify must or wine in that it requires no extra equipment or additives. However, it takes the most time and there is a cost to the energy used in chilling. It is also a batch process, which, again, costs in labour and time. For these reasons, it is most commonly used for small-volume production of premium wines.
Explain Flotation
Flotation involves bubbling gas up through the must. As the bubbles of gas rise, they bring with them the solid particles. The solid particles are then skimmed off the top of the vessel. Compared to sedimentation, flotation speeds up the rate of clarification. Inert gas such as nitrogen is typically used. If oxygen is used as the gas, this is a method of hyperoxidation. Fining agents must be added to the must for this technique to be successful (to help bind the particles together), and it can it only be used on must, not wine. This technique is a little more expensive than sedimentation in terms of the equipment needed; however, it is effective and quick, and can either be used as a continuous or a batch process. The technique requires gases, fining agents and equipment for bubbling the gas through the liquid. However, the must does not need chilling, and therefore there is a saving on energy costs.
Explain Clarification
Between pressing and fermentation, the juice of white grapes may be clarified. Clarification may also occur after fermentation. The aim of clarification is to reduce the amount of suspended solids within the must. These solids include particles of grape skin, stem and seeds.
Winemakers will generally aim for the proportion of solids in the must to be 0.5–2 per cent. Some winemakers choose to retain higher proportions of solids, and may not clarify the must at all because this can add to the texture of the wine, giving a subtle astringency (particles of skin and stem will add tannins). Relatively high levels of solids can give a greater range of aromas from fermentation, which can give greater complexity; however, lower levels of solids are better for obtaining fruity aromas. Therefore, a relatively high level of solids may be desirable for a premium-priced Chardonnay, but would be less suitable for an inexpensive Pinot Grigio. Fermentations with a high level of solids need careful monitoring and management as the various compounds within the solids and their reactions can lead to off-flavours. For example, high solids fermentations can give reductive sulfur compounds that at low levels may be desirable (struck match, smoke), but at higher levels are very negative for quality (aromas of rotten eggs). It is therefore a technique better suited to small-volume, premium production.
However, a small amount of solids is beneficial in that it provides nutrients for yeast, and over-clarifying the must can lead to stuck fermentations.
Explain Fining
Fining is a procedure in which a fining agent is added to speed up the process of precipitation of particles. Fining agents can be of protein or mineral origin. Fining removes a small proportion of unstable colloids (microscopic particles too small to be removed by filtering) from the wine. It helps to clarify the wine and to stabilise it against the formation of hazes later in the bottle.
Winemakers conduct lab trials before using fining agents to ensure that the minimum effective amount is used. They then compare the fined sample with the original wine before proceeding. Many fining agents can remove positive compounds from wine or make the wine unstable when too much is added (over-fining) and therefore it is important to only add the minimum effective amount.
In addition to clarifying the wine, each fining agent has particular properties that can offer solutions to problems such as the removal of harsh tannins in red wines or browning in white wines. The fining agent must have the opposite charge from the wine colloid to be removed. The fining agent and the colloid attract each other and form a solid large enough to be removed by racking or by filtration.
Explain two mineral and two protein fining agents
Bentonite – A form of clay which adsorbs (holds molecules of a gas, liquid or solute as a thin film on the outside surface or on internal surfaces within the material) unstable proteins and unstable colloidal colouring matter. It has a minimal effect on the flavour and texture of wine. It does lead to some colour loss in red wines and produces large amounts of sediment, and so wine is lost when it is racked off.
Charcoal – This removes brown colours (e.g. to create Pale Cream Sherry) and some off-odours. Care has to be taken as charcoal over-fines easily removing desirable aromas and flavours. One option is to treat only one batch of the affected wine and then blend it with the rest of the wine to reduce this effect.
Egg white – Due to its protein content, egg white is often used in fresh or powdered form. It tends to be used for high-quality red wines because of its ability to remove harsh tannins and clarify wine. It is gentle to the wine. As it is an allergen….
Isinglass – A protein collagen that very effectively clarifies white wines, giving them a bright appearance. The smallest effective amount must be added to avoid potential for the formation of a protein haze later and the creation of a fishy smell. It is not suitable for vegetarians as it is derived from fish bladders.
