Proteins are present in wine. The most common protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s include thaumatin

Thaumatin

Thaumatin is a low-calorie sweetener and flavour modifier. The substance, a natural protein, is often used primarily for its flavour-modifying properties and not exclusively as a sweetener....

-like proteins and chitinase

Chitinase

Chitinases are hydrolytic enzymes that break down glycosidic bonds in chitin. As chitin is a component of the cell walls of fungi and exoskeletal elements of some animals , chitinases are generally found in organisms that either need to reshape their own chitin or dissolve and digest the chitin of...

s and have a role in the formation of turbidity

Turbidity

Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....

 (haze) especially visible in white wine. The quantity of haze forming is dependant on the quantity of phenolics in the wine.

Some of those proteins are considered nuisance

Nuisance

Nuisance is a common law tort. It means that which causes offence, annoyance, trouble or injury. A nuisance can be either public or private. A public nuisance was defined by English scholar Sir J. F...

. Some of them are grape

Grape

A grape is a non-climacteric fruit, specifically a berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or they can be used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, molasses and grape seed oil. Grapes are also...

 pathogenesis-related protein

Pathogenesis-related protein

Pathogenesis-related proteins are proteins produced in plants in the event of a pathogen attack. They are induced as part of systemic acquired resistance.Many proteins found in wine are grape pathogen-related proteins...

s. Those proteins have been identified by mass spectrometry and originate from grape, yeast, bacteria and fungi.

These proteins are unstable when submitted to heat but can be removed with treatment with bentonite

Bentonite

Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...

, process called clarification and stabilization of wine

Clarification and stabilization of wine

The clarification and stabilization of wine in winemaking involves removing insoluble and suspended materials. The insoluble material causes a wine to be cloudy. These processes may include fining, filtration, centrifugation, flotation, refrigeration, barrel maturation, pasteurization and racking...

.

Proteins residues from proteinaceous fining agents such as gelatin

Gelatin

Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...

 or egg white

Egg white

Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...

 can possibly be found in wine. Wheat gluten

Wheat gluten

Wheat gluten can refer to:* The gluten found in wheat, a sticky substance composed of the proteins gliadin and glutenin* Wheat gluten , a food prepared from these proteins, such as seitan or wheatmeat...

 has also been tested but there are health issues regarding its use because of gluten intolerance in some people.