Winery measurements: what does a hydrometer measure during crush and fermentation? Choose the parameter primarily measured by a standard winemaker’s hydrometer floated in grape juice or must.

Introduction / Context:
Hydrometers are simple, essential tools in wineries. By floating in juice or must, they indicate density, which correlates to sugar concentration. This helps determine harvest ripeness, ferment progress, and potential alcohol.

Given Data / Assumptions:

• Instrument is a floating hydrometer or saccharometer calibrated for wine use.
• Sample is grape juice or fermenting must.
• Reading is in specific gravity, Brix, or Baumé depending on scale.

Concept / Approach:
Sugars (glucose and fructose) elevate must density compared with water. As yeast convert sugar to ethanol and CO₂, density falls. Hydrometers thus infer sugar levels (and by calculation, potential alcohol). They do not directly measure acidity, ethanol in finished wine (without distillation correction), dissolved oxygen, or sulfur dioxide.

Step-by-Step Solution:

Verification / Alternative check:
Refractometers also measure sugar (Brix) optically; hydrometer trends match refractometer readings pre-fermentation, confirming use for sugar assessment.

Why Other Options Are Wrong:

• TA, DO, FSO₂ require titration or specialized probes; not hydrometers.
• Alcohol content is not directly read by a standard hydrometer in finished wine without distillation/temperature correction.

Common Pitfalls:
Ignoring temperature correction factors; CO₂ bubbles can cause falsely low density readings during active fermentation—degas samples.

Final Answer:
Grape sugar via density (specific gravity/Brix)