Colloids colors

Wines do not necessarily stabilize in the first year. If warm temperatures promote the combination of tannins and polysaccharides and the medinm still has a high enough concentration of colloidal molecnles of the same type, more colloidal coloring matter may be formed. To avoid this repeated precipitation, it is possible to use protective colloids (Section 9.4) and eliminate all the colloids by fining (Section 10.4). Protective colloids, snch as gum arabic (Section 9.4.3) and mannoproteins (Section 5.6.3), prevent the flocculation of nnstable colloids, maintaining the particles in snspension rather than eliminating them. 

These nnstable colloids are deposited in layers, coating the sides of the bottles. Solubilization tests on these particles show that they are very different from colloidal coloring matter, as formic acid mixed with methanol is only capable of dissolving a small fraction of the deposit. Besides tannins... 

Among the colloids found in wine, proteins and cellulose fibers are positively charged, while yeast cells and bacteria, colloidal coloring matter, ferric phosphate, copper sulfide, ferric ferrocyanide and bentonite are negatively charged. 

Most wines certainly contain mucilaginous substances that act as protective colloids mannoproteins. Their existence is demonstrated by the elimination of the protective effect after fine ultrafiltration or dialysis. This phenomenon is well known in red wines, where colloidal coloring matter and tannins inhibit tartrate precipitation. It also exists in white wines and may be attributed to neutral polysaccharides (gum). According to the desired result, these substances may either be eliminated by fine filtration (e.g. to facilitate tartrate stabilization) or, on the contrary, protective colloids such as gum arabic may be added to a clear wine just before bottling to compensate for insufficient natural protection. 

It has a permanent effect. As colloidal coloring matter is known to form regularly during aging, a wine may again be unstable at cold temperatures only a few months after fining. 

Another application for gum arabic is in the production of vins de liqueurs, rancio wines, aperitifs, vermouth, port, Pineau des Charentes, etc. As these products are frequently stored in contact with air and their aging process includes deliberate oxidation, the formation and precipitation of colloidal coloring matter is the main cause of turbidity. Gum arabic, at doses of 20-25 g/hl, prevents flocculation of the coloring matter. This treatment is not recommended for wines of this type intended for long bottle aging. 

Bentonite treatment is used to prevent protein problems in white wines (Sections 5.6.2 and 5.6.3), but it is also very effective for clarifying red wines and stabilizing colloidal coloring matter. Finally, siliceous earths and polyvinylpolypyrroli-done (PVPP) may also be useful for clarifying certain wines. 

If there is a risk of overfining, it is advisable to test for excess, non-flocculated proteins (Section 5.5.4). Heating to 80°C is not always sufficient to show up the excess proteins corresponding to overfining, so it is advisable to add tannins as well. Red wines may also be chilled to assess the stabilizing effect of fining on the precipitation of colloidal coloring matter. 

Bentonite 20-50 g/hl Clarification of young wines. Eliminates colloidal coloring matter. Facilitates sedimentation of protein fining agents... 

The use of heat to accelerate maceration phenomena is described elsewhere (Volume 1, Section 12.8.2). Cold stabilization is also effective for eliminating insoluble compounds such as tartrates (Sections 1.7.2-1.7.4) or colloidal coloring matter in red wines (Section 6.8). Cooling is also... 

It is well known that some of the coloring matter in red wines is colloidal. It is soluble at normal temperatures but precipitates at low temperatures (0°C), causing turbidity in the wine. This colloidal coloring matter gradually becomes less soluble throughout the winter, due to the drop in temperature. It settles out to form part of the lees of young wines. 

The other elements in a wine s chemical composition (polyphenols, polysaccharides, amino acids and volatile compounds) are not greatly affected by electrodialysis. In particular, this treatment has less effect on the colloidal coloring matter of red wines than cold stabilization. 

The combinations formed when tannins react with bniky polymers are colloidal. They precipitate dnring aging when Brownian motion decreases due to low temperatures. This is the origin of colloidal coloring matter in wine. 

Low temperatures, on the contrary, do not cause any particular problems, but rather facilitate the precipitation of colloidal coloring matter. Oxygen dissolves more easily, leading to oxidation of the medium, and various reactions take place more slowly. However, it is not advisable to keep wine at low temperatures for too long, as development is inhibited and there is a significant risk of oxidation, but a few weeks exposure to cold is strongly recommended. 

Firstly, clarity is easier to obtain when wine is aged in the barrel rather than in the vat, due to the smaller volume. Clarification is also facilitated by the adsorption phenomena that occur in oak. Furthermore, wine in the barrel is more sensitive to outside temperature, so the precipitation of salts, particles and colloidal coloring matter is much more likely to be triggered by winter cold. 

Au and Cu nylon11 composites were obtained by a simple technique, the RAD process, which involves heating of the quenched nyloni 1 on which Au or Cu was costed. Au or Cu are found to exist in the nyloni 1 in the form of ultrafine Au or CuzO particles, dispersing umformfy without agglomeration. Au- and Cu-nytonlt composites showed the constituent colloidal colors, ruby red and yeliow, respectively. 

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