Sulfite management in winemaking: Why is sodium or potassium metabisulfite commonly added to freshly crushed grapes?

Introduction / Context:
Sulfite additions (typically as potassium or sodium metabisulfite) are standard practice in winemaking. They help manage microbial populations and oxidative reactions in musts and wines, protecting sensory quality and fermentation outcomes.

Given Data / Assumptions:

• Crushed grapes contain native microflora (yeasts, bacteria, molds).
• Oxygen exposure can trigger enzymatic browning and aroma loss.
• Sulfite dosing must be controlled to avoid sensory faults and legal limit issues.

Concept / Approach:
Metabisulfite releases SO2, which exhibits antimicrobial and antioxidant properties. At appropriate levels, SO2 suppresses spoilage microbes, favors desired Saccharomyces strains, and protects against oxidative browning by binding oxygen radicals and inhibiting polyphenol oxidases. SO2 does not primarily serve to lower pH or create flavors; its effect on flavor is protective rather than generative.

Step-by-Step Solution:

Verification / Alternative check:
Comparisons of sulfited vs. unsulfited musts consistently show reduced spoilage and browning, with cleaner fermentations when SO2 is used properly.

Why Other Options Are Wrong:

Common Pitfalls:
Overdosing sulfite (sensory issues) or underdosing (spoilage risk); ignoring free vs. bound SO2 dynamics and pH-dependent efficacy.

Final Answer:
To suppress undesirable microorganisms and protect the must.