Colloids
The particles in freshly made wine can be categorised into three groups:
| Particle Size | Description |
|---|---|
| < 2 nm | Simple molecules such as alcohols, sugars and acids. These form solutions in the wine, are a necessary part of its structure and remain in it through all treatments. |
| 2 – 1000 nm | Substances with large molecules, but not sufficiently large to render themselves visible by causing cloudiness. They are also not large enough to be removed by a filter. These constitute the group of substances known as ‘colloids’. |
| > 1000 nm | Large particles such as pieces of grape cell, yeasts and other substances all of which contribute to the cloudiness of the wine. These can be removed by sedimentation or filtration. |
Colloids are:
- Positively or negatively charged
- Neither in true solution or suspension, but in a colloidal dispersion
- Between 2 – 1000 nm in diameter, and thus can pass through filters and settle only very slowly, if at all. Fine filters can actually become blocked due to colloids in the wine.
- Unstable and may cause the wine to become cloudy after filtering and bottling.
The molecules of these unstable colloids carry an electrostatic charge. This is the same charge for each molecule - these like-charged molecules repel each other, which keep them apart – keeping them suspended and rendering them invisible. With age and changes in temperature or light, the molecules lose their charge, enabling them to clump together (flocculate). This material is harmless and tasteless, but can form a haze or deposit in the wine.
The above diagram is by David Bird MW from “Understanding Wine Technology”
| Negatively charged | Positively charged | |
|---|---|---|
| Naturally-occurring (wine) colloids: | Tannins Pectins Dextrans and glucans |
Coloured phenolics Proteins |
| Added colloids: | Bentonite Gum Arabic DE (Kieselguhr) |
Protein finings Cellulose |
Tag:
