Fining protein agents

The second type is a stable dispersion, or foam. Separation can be extremely difficult in some cases. A pure two-component system of gas and liquid cannot produce dispersions of the second type. Stable foams can oe produced only when an additional substance is adsorbed at the liquid-surface interface. The substance adsorbed may be in true solution but with a chemical tendency to concentrate in the interface such as that of a surface-active agent, or it may be a finely divided sohd which concentrates in the interface because it is only poorly wetted by the liquid. Surfactants and proteins are examples of soluble materials, while dust particles and extraneous dirt including traces of nonmisci-ble liquids can be examples of poorly wetted materials. 

Sami-Manchado, P. et al.. Analysis and characterization of wine condensed tannins precipitated by proteins used as fining agent in enology. Am. J. Enol. Viticult., 50, 81, 1999. 

Follow-up studies utilized finely-milled legume flours and the addition of soybean flour as a fat-control agent in an effort to improve doughnut quality (5). The legume products and doughnuts prepared from them are shown in Figure 5. On a dry weight basis, peanut flour from solvent extracted peanuts (PF-SE) contained 0.9% fat and 54.4% protein while cowpea flour (CF) contained 1.4% fat and 25.5% protein. Peanut flour from partially defatted untoasted peanuts (PF-PD-U) contained 34.5% fat and 34.9% protein while peanut flour from partially defatted peanuts toasted at 160°C contained 34.4% fat and 37.6% protein. 

Fining also may be done to juice prior to fermentation. Protein fining agents may be used to reduce phenolics in press juice, or bentonite used for protein reduction or reduction of potential for hydrogen sulfide (H2S) production (18). 

Fining is a winemaking technique used to enhance sensory or clarity properties of the wines. Common fining agents used with North Coast white wines are bentonite (a clay), casein (milk protein), gelatin (animal protein),... 

A disk-stack centrifuge is used for cell harvesting. A high-pressure ho-mogenizer is utilized to break the cells and release the inclusion bodies. These inclusion bodies are recovered in another disk-stack centrifuge. The inclusion bodies are then solubilized in a well-mixed reactor with urea. This chaotropic agent dissolves the denatured protein. A filter is used to remove the fine particles such as biomass, debris, and inclusion bodies. 

The most commonly used fining agents in the wine industry are bentonites (mainly containing montmorillonite) and proteins associated to tannins or a mineral agent. Gelatin has also been used in enology since the nineteenth century, but due to the crisis of the mad cow disease in 1999, plant proteins have widely been experimented and are now more and more used on an industrial scale. For this reason, this chapter will essentially focus on bentonite as well as plant proteins. 

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