Did you know you can use sugar to figure out how much alcohol is in something? It's really simple, but I still see a lot of people messing it up, so here's everything you need to know about how to measure alcohol in mead, wine, and beer when homebrewing.
What a Hydrometer Actually Does
A hydrometer is a little glass tool that just floats. You drop it into your liquid and read where the surface hits the scale printed on the side. That's it. No batteries, no calibration headaches, nothing complicated.
The value you're reading is called specific gravity, and it tells you how much sugar is dissolved in your liquid. The more sugar present, the higher the hydrometer floats. Less sugar, and it sits lower in the liquid.
Here's why that matters for us as brewers. Yeast eats sugar and converts it into alcohol during fermentation. So as fermentation progresses, that sugar content drops, and your hydrometer reading drops right along with it. Take a reading before fermentation starts and another after it finishes, and you can calculate exactly how much alcohol got made.
How to Take a Reading Step by Step
- Fill a graduated cylinder (or your fermenter, if it's wide enough) with a sample of your must or mead.
- Gently lower the hydrometer into the liquid and give it a light spin to knock off any bubbles clinging to the glass.
- Let it settle until it stops bobbing.
- Read the number at the point where the liquid surface crosses the scale, looking at it at eye level.
- Record the date and the reading before you dump the sample back or toss it.
That number is your specific gravity. Simple as that.
A Real Example
Say I just made a batch of mead. It's loaded with honey, hasn't started fermenting yet, and my starting gravity measurement comes out to about 1.106.
Thirty days later, the yeast has done its job. That sugar is now alcohol, so the hydrometer doesn't float nearly as high anymore, and my reading has dropped all the way down to 1.000.
Use Subsequent Readings to Know When Fermentation Is Done
Don't just take one reading at the start and call it good. I recommend taking your initial gravity, then checking again weekly as fermentation goes on. Once your gravity reading stops changing for two weeks in a row, fermentation is finished. If it's still dropping, even slowly, leave it alone and keep checking back.
This is really the only reliable way to know your mead is actually done and not just fermenting slowly. Airlock activity can fool you. The hydrometer doesn't lie.
Calculating Your ABV
Once fermentation is complete, take the difference between your starting gravity and your final gravity, then multiply that difference by 131.25. That gives you your alcohol by volume, or ABV.
In our example: 1.106 minus 1.000 gives you 0.106. Multiply that by 131.25 and you land right around 13.9% ABV. That's all there is to it.
What Your Final Gravity Tells You About Sweetness
Your final gravity doesn't just tell you about alcohol, it also gives you a rough idea of how sweet your finished mead will be. Based on the ranges I use in my own recipes:
- Below 1.010: dry
- 1.010 to 1.020: semi-sweet
- 1.020 to 1.030: sweet
- Above 1.030: dessert style
Keep in mind that perceived sweetness is also affected by acidity, so two meads with the exact same final gravity can taste noticeably different depending on the recipe.
A Callout on Backsweetening and Your ABV
If you plan on backsweetening your mead (adding more honey or juice after fermentation to bump up the sweetness) there's a wrinkle you need to account for. Adding that extra volume dilutes your finished mead slightly, which means the ABV you calculated from your original starting and final gravity readings won't be perfectly accurate anymore.
If precision matters to you, factor in the added volume when you recalculate your ABV after backsweetening, since the alcohol is now spread across more total liquid. And remember, any sugar you add after fermentation needs to be paired with proper stabilizing first, or you risk restarting fermentation in a sealed bottle. I go through that whole process in my Mead Making Guide if you want the full breakdown.
A basic hydrometer is one of the few tools I consider non-negotiable for homebrewing. I include one in my Mead Making Starter Kits for exactly that reason, since you really can't dial in your recipes without one.
People Also Ask
Do I need a hydrometer to make mead? You don't strictly need one to make mead, but you're flying blind without it. Without a hydrometer you have no real way to know your alcohol content or confirm fermentation is actually finished.
Can I reuse my hydrometer sample? I wouldn't pour it back into your batch once it's touched a hydrometer, since that risks introducing contamination. Treat it as a discard sample.
Does temperature affect my hydrometer reading? Yes, most hydrometers are calibrated to read accurately at a specific temperature, usually 60°F or 72°F depending on the brand. If your sample is a lot warmer or colder than that, your reading will be slightly off. Check the calibration temperature printed on your hydrometer.
What if my gravity reading never changes? If your gravity stalls out well above 1.000 and hasn't moved in two weeks, your fermentation may have stopped early due to a stressed yeast population, high starting gravity, or a nutrient deficiency, not because it's actually finished.