Post-Fermentation Clarification Flashcards
Explain Sedimentation
If wine is stored in cool cellar conditions, it will begin the process of clarification naturally, with suspended matter precipitating over time. The wine is allowed to stand and the particles with higher density than wine will form a sediment at the bottom of the container. The wine can then be racked off, leaving the sediment behind.
What is the advantage and disadvantage to sedimentation?
Some winemakers believe that clarification by sedimentation avoids the potential loss of texture and flavour that may occur if the wine is fined or filtered.
As sedimentation takes time, this has a cost as the wine cannot be sold until it is ready to be released. This means that sedimentation is usually only suitable for premium or super-premium priced wines. However, if a wine is to be barrel-aged, then sedimentation will happen as part of the barrel ageing process.
What is Fining?
Fining is a procedure in which a fining agent is added to speed up the process of the precipitation of suspended material in the wine. 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.
What is a fining agent that removes unstable proteins?
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.
What are fining agents that remove phenolics that contribute undesirable colour and bitterness?
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.
Gelatin – A protein collagen extracted from pork that aids clarification, removes bitterness and astringency in red wine and browning in white wine pressings. It must be added in the smallest effective amount as it is easy to over-fine with gelatin, stripping flavour and character, and creating the risk of a protein haze forming later. It is not suitable for vegetarian wine as it is derived from animals.
Casein – A milk-derived protein that removes browning from white wines and clarifies wines to some extent. It must be declared as an allergen on the label in some territories.
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.
Vegetable protein products – These are derived from potato or legumes and are suitable for vegan-friendly wines.
PVPP – Polyvinylpolypyrrolidone is an insoluble plastic in powder form that removes browning and astringency from oxidised white wine. It is a gentler fining agent than charcoal. It is rarely used on red wines, but can reduce astringency and brighten the colour.
What fining agent removes colour and off-odours?
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.
Explain Filtration.
Filtration is a physical separation technique used to eliminate solids from a suspension by passing it through a filter medium consisting of porous layers that trap solid particles, thus making the liquid clear. Filtration is the most common way of clarifying wine.
There are two main types, depth filtration and surface filtration.
Explain Depth Filtration.
This method of filtration traps particles in the depth of the material that forms the filter. It can cope with fluid with many particles in it; for example, wine that has just been pressed or lees. Small particles are trapped within the many irregular channels through the filter. This type of filter does not block easily; however, it is not absolutely reliable because, if too much pressure is applied or if the filter is used for too long, some particles will make their way through the filter. In other words, it is not an absolute filter.
Name the most common way to depth filter and explain it.
The most common form of depth filtration is by using diatomaceous earth (‘DE’, also known as Kieselguhr), which, once it has been processed, is pure silica and inert:
Rotary vacuum filters use this method to filter very thick and cloudy wine (e.g. wine mixed with lees). It is an oxidative process as the drum is exposed to air.
Enclosed DE filters do the same job, but can be flushed with an inert gas (e.g. nitrogen) to avoid oxidation taking place.
DE comes in a range of particle sizes and thus can remove large or very small (e.g. yeast) particles.
Used DE must be disposed of responsibly, which adds an additional cost.
What is the form of depth filtering that is also known as ‘plate and frame’? Explain it.
Sheet filters – These are also known as ‘plate and frame’ or ‘pad’ filters. The wine is passed through a sheet of the filtering material. The more sheets there are in the filter, the quicker the wine can be filtered because any portion of wine only passes through one sheet.
Very fine graded sheets can be used to remove any remaining yeasts at bottling.
Sheet filter systems require investment initially (the frame must be very robust to withstand the pressures involved), although the cost of filter sheets is low. Trained personnel must operate them to work properly.
Explain Surface filtration.
A surface filter stops particles that are bigger than the pore size of the filter from going through. They are often termed absolute filters. There are two types of surface filter: membrane filters and crossflow filters.
What are Membrane filters and the advantages and disadvantages?
Membrane filters – These filters, sometimes also called cartridge filters, catch particles that will not go through the pore size of the filter. They are slower than using a depth filter as the pores are smaller, often less than 1 micron. For the same reason, wine must be pre-filtered first (e.g. by depth filtration) as, otherwise, membrane filters can easily get blocked. They are usually used as a final precaution immediately before the wine is bottled to ensure that the wine is completely clear and microbiologically stable. This is sometimes called sterile filtering, but this is not entirely accurate; the point is that yeasts and bacteria have been removed and therefore the wine is microbiologically stable. In contrast to depth filters, the initial investment is small, but the cartridges are expensive. This is a very common form of filtration during the bottling/packaging process.
What are Cross-flow filters and the advantages and disadvantages?
Cross-flow filters – These are also known as tangential filters. They allow wine to pass through the filter while uniquely cleaning the surface of the filter as it works. Solid particles cannot pass through the filter. Cross-flow filters can filter wine with a high load of particles or lees very quickly. There are no replacement sheets, cartridges or earth to buy or dispose of. However, the machines are expensive, making them more suitable for large and or well-funded wineries
