What it actually measures
A hydrometer doesn't measure "whether it's fermenting" — it measures the dissolved sugar in the must. As yeasts consume that sugar and convert it into alcohol, the liquid's density drops. That drop, not the number itself, is what tells the winemaker how the process is going.
How to read it right
The reading is taken at the meniscus line, the point where the liquid's surface crosses the instrument's scale — not at the upper edge, where the liquid climbs slightly due to surface tension. On top of that, hydrometers are calibrated at a reference temperature: a reading taken at a different temperature gives an incorrect value if it's not corrected, even if the instrument is perfectly calibrated.
The most common mistake: a single reading tells you nothing
Seeing one isolated number doesn't tell you whether fermentation is progressing normally, slowing down, or already finished. What matters is the trend: comparing today's reading with yesterday's. A density that's dropping steadily signals a healthy fermentation; one that stops dropping, even temporarily, is the first sign something might be going wrong.
What the number says throughout fermentation
At the start, density is high because of the dissolved sugar. As fermentation progresses, it drops steadily. When it stabilizes near water's density, there's no more fermentable sugar left — that's when alcoholic fermentation is considered done.
Why this instrument matters so much: it's the only real, objective way to know whether a fermentation is progressing — everything else (color, bubbling, smell) gives clues, but only density gives a number you can track over time.
How LagarLab trains this
The simulator uses the same instrument, the same units, and shows the full fermentation curve, not just an isolated reading — so someone learns to read the trend, not a lone number, before having to do it on a real tank.
Want your team to master this instrument before the next harvest?
One payment covers the whole winery team — no per-seat billing.
Enter the laboratoryFrequently asked questions
What does a hydrometer actually measure in must?
Dissolved sugar, not fermentation itself. Density drops as yeasts consume that sugar, and that drop is what's used to track the process.
Why does temperature matter when reading a hydrometer?
Hydrometers are calibrated at a reference temperature. Reading it at a different temperature without correcting gives an incorrect value, even if the instrument works perfectly.
Is a single density reading enough?
No. A single number doesn't tell you whether fermentation is progressing, has stalled, or is done — you need to compare it with the previous reading to see the trend.
How much does it cost to train the whole team on this?
450 USD per semester or 720 USD per year, for up to 30 people — no per-seat billing.
What do the markings on a wine hydrometer mean?
Most wine hydrometers have up to three scales. Specific gravity compares the liquid's density with water, which reads 1.000; a must ready to ferment usually reads between 1.080 and 1.110. The Brix (or Balling) scale shows the sugar content directly, and the potential alcohol scale estimates how much alcohol that sugar can become. As sugar turns into alcohol the reading drops, and a dry wine ends slightly below 1.000, because alcohol is lighter than water.