Colloids Flashcards
What are colloids in wine?
Particles 2-1000 nm in size that form colloidal dispersions; neither fully dissolved nor suspended, and slow to settle.
What distinguishes colloids from standard suspensions?
Colloids (2-1000 nm) pass through filters, are microscopic, and settle slowly; suspensions (>500 nm) block filters and settle easily.
What are the two types of colloids?
- Macromolecules (polysaccharides, proteins). 2. Aggregates (condensed phenols, coloring matter, metal casse).
Why are colloids unstable?
They carry charges (positive/negative) that repel each other, but may agglomerate under certain conditions, causing cloudiness.
What is the isoelectric point (pI)?
The pH at which a molecule (e.g., protein) has no net charge, causing it to precipitate.
How does pH affect protein charge?
At pH < pI: net positive charge. At pH > pI: net negative charge. Most wine proteins have pI of 5.5–8.
What forces cause colloid agglomeration?
Van der Waals forces, electrostatic attraction, thermal energy, hydrophobic interactions, and absorption.
What are protective colloids?
Substances (e.g., gum arabic) that enhance colloidal dispersion, preventing agglomeration.
What factors slow natural sedimentation?
Electrostatic repulsion, thermal currents, gas bubbles (CO₂), and small/light particles at the tank top.
What are advantages of natural sedimentation?
Low cost, minimal processing, ‘natural’ method. Disadvantages: Very slow, may not work for all colloids.
What is splash racking?
Racking wine with splashing into receival tanks/barrels to reduce sulphide off-aromas, common post-fermentation.
How does a centrifuge clarify wine?
Uses centrifugal force to rapidly separate particles; efficient but requires skilled operation and careful desludging.
What are centrifuge disadvantages?
Expensive, complex, high wine loss (older models), bentonite issues, and difficult cleaning.
What negatively charged colloids exist in wine?
Tannins, pectins, dextrans, bentonite, gum arabic. Positively charged: proteins, colored phenolics.
Why use fining agents?
To neutralize colloid charges (e.g., negative bentonite binding positive proteins), forcing flocculation and precipitation.
