Colloids Flashcards
What are colloids in wine?
Colloids are particles between 2-1000 nm in diameter that are neither true solutions nor suspensions and can cause cloudiness in wine after filtering and bottling.
Colloids are unstable and may pass through filters, making them a significant concern in winemaking.
What types of solids are found in wine after fermentation?
- Non-viable yeast
- Yeast autolysis components
- Enzymes
- Nitrogen compounds (amino acids, peptides, nucleotides)
- Mannoproteins & other polysaccharides
- Bacteria
- Tartrates
- Agglomerated proteins
- Precipitated tannins
- Complexes of the above
These solids can contribute to both flavor and stability of the wine.
What is the difference between standard suspensions and colloidal suspensions?
Standard suspensions have solids >500 nm, are visible under a microscope, and settle easily, while colloidal suspensions have solids 2-1000 nm, are not visible under a microscope, and settle slowly.
This distinction is important for understanding how different particles behave in wine.
Define the isoelectric point (pI).
The isoelectric point (pI) is the pH at which a molecule has a net neutral charge, balancing positive and negative charges.
At pH = pI, proteins have no net charge.
At what pH range do most proteins have their isoelectric point?
Most proteins have a pI between 5.5 and 8.
Understanding this range helps in managing protein behavior in winemaking.
What factors influence colloid stability?
- Attractive forces: Van der Waals forces, electrostatic forces, thermal energy, hydrophobic interactions, absorption
- Repulsive forces: Thermal energy, electrostatic forces, hydrophilic interactions
The balance between these forces determines whether colloids remain dispersed or agglomerate.
What are the three main approaches to clarifying wine with colloids?
- Changing wine conditions (e.g., adjusting pH, TA)
- Using protective colloids
- Using fining agents
Each approach affects colloid behavior and helps clarify the wine.
What is natural sedimentation in winemaking?
Natural sedimentation is the process where solids settle out of the wine due to gravity, slowed by electrostatic repulsion, thermal convective currents, and CO2 bubbles.
It is a cost-effective method but can be slow.
What is the purpose of racking in winemaking?
Racking involves transferring clarified wine off the sediment to improve clarity.
Techniques like racking plates and positive displacement pumps are used.
What are the advantages of centrifugation in wine clarification?
- Quick clarification
- High clarity possible
- Can handle very turbid wine
- Low wine losses with newer machines
Centrifugation uses centrifugal force for faster clarification compared to gravity.
What are the disadvantages of using centrifugation?
- Expensive
- Complicated
- Prone to misuse
- High wine losses with older machines
- Difficult to clean
- Requires trained operators
These factors may limit the use of centrifugation in some winemaking operations.
Fill in the blank: Colloids in wine are typically classified into _______ and _______.
[macromolecules, aggregates or complexes of smaller molecules]
Examples include polysaccharides, proteins, condensed phenols, and coloring matter.
True or False: Colloids can act as both positively and negatively charged particles.
True
This dual charge behavior is significant for their interactions in wine.
What is the effect of protective colloids in winemaking?
Protective colloids increase the dispersal of other colloids and can help maintain clarity in wine.
This is important for preventing unwanted cloudiness.
