Bentonite

This consists of negatively-charged particles and so removes positively-charged proteins such as enzymes (oxidases), vitamins and amino acids, thus increasing microbial and heat stability. There is some flavour reduction but the lees are said to settle faster and better in wines with added bentonite. It is normally used for protein stability in whites and rosés; in red wines, the tannins precipitate out any protein in the wine, so bentonite is not required. There are two types of bentonite, calcium and sodium bentonite. Bentonite usually needs swelling in 10 times it own weight of water for 24 hours before addition. Note that varieties grown in the UK, often have very high protein levels and can require bentonite addition of up to 3000 mg/l.

Gelatine

Gelatine is a protein extracted from animal bones or hides by boiling. The preparation should be odourless and colourless and is sold as a powder which requires dissolution in warm water (30°C) into an 8 -10% solution before use, or as a liquid. Gelatine is a good clarifier and can remove off-tastes, but reduces body in wines. The ideal temperature in which to use it is 16 - 25°C. Thorough and immediate mixing is very important. Gelatine is recommended for white wines from rotted vintages as it will remove some astringency and off-tastes. In red wines it will also increase suppleness, but will remove 5-10% colour in young wines and more in old. If too much gelatine is added to a white wine (over-fining) the wine can then become protein-unstable, and will need to be counter-fined with tannin or silica sol.

Egg Albumen

Egg albumen is produced from the white of chicken’s eggs in fresh, frozen or powdered form. If powdered egg white is used, it must be gently mixed with water, whipping lightly to avoid the formation of froth, which forms a meringue on the surface of the wine. 5 -8 fresh egg whites per barrel are used on many great French red wines. They must first be diluted up to 250 ml with water, and a pinch of salt is often added to help flocculation. Egg albumen is not suitable for white wines, as high levels of tannins are required for flocculation. It is the best fining for red wines as, although it clarifies the wine poorly, it removes the colloidal phenolics, and renders the wine supple without removing too much colour or flavour.

Casein

Casein is the principal protein of milk. It is a poor clarifying agent but is used to remove excess colour, oxidised character and reduce the iron content of the wine. It is often used for Sherries. It does not over-fine, as its flocculation is mostly due to wine acidity. It is most effective at 15-20°C, and must be mixed thoroughly and rapidly, as it coagulates (curdles) as soon as it mixes with the wine. Milk can be used if considerable colour removal and deodorisation is required. Skimmed milk is not as good for colour removal, but its fining action is greater. The recommended dose is 2 - 4 ml/l. The disadvantage with milk is that it can lead to over-fining at very high doses, and provides a wide range of nutrients for bacterial growth.

Activated carbon (charcoal)

Derived from burnt animal or plant matter, carbon fining is often used as a last resort to remove off-odours and colour. It is best used in conjunction with 50 mg/l ascorbic acid, as otherwise it may provoke oxidation. Often used at low doses for final pressings.

Isinglass

Isinglass is a protein found in the air bladder of fish (especially sturgeon), and prepared as fine chips which must be mixed with water as a 1% solution without heating.
Isinglass flocculates on contact with wine due to the wine’s tannin content, and falls to the bottom of the vessel, removing particles by screening and electronic attraction.
It is commonly used for white wines, just before bottling. This is because it gives a better ‘sparkle’ than gelatine and is less detrimental to wine colour and flavour. It never over-fines, although it may require a little aeration to flocculate, and too much may result in a fishy nose and palate. Its disadvantages are that it produces small amounts of light, fluffy lees which clog filters, and it is very expensive and difficult to prepare.
However, cheaper and easier to use fish-based fining agents are commercially available.

PVPP (Poly-vinyl Poly-Pyrrolidone)

This fining agent removes lower molecular weight phenolics, and so is often used to reduce bitterness in wines, particularly white wines which have undergone skin contact. It also can reduce browning, by removing phenolic material that may brown. It has little effect on astringency.

Silica sol

A colloidal suspension of silicon oxide, used to help flocculate fining agents such as gelatine. This can improve clarity and reduce volume of lees produced.

Yeast

High doses of fresh yeasts are sometimes added to wines to remove off-odours. Yeast hulls can also be used.