Specific Gravity (S.G.) is the winemaker’s compass reading – it can tell us where the wine is in its fermentation process and is very important to stay on track and not get lost along the way.
• How do we get these readings? Through a device called a hydrometer. Click here to see instructions on how to use a hydrometer to obtain an S.G. reading.
• How does it work? A hydrometer measures the density of liquid. As sugar in the wine is replaced by less dense alcohol (the job our trusty yeast friends are busy doing), a lower reading is given on the hydrometer. Using this information, you will be able to know if your wine is fermenting and when fermentation is complete.
A hydrometer is a tool used to measure Specific Gravity (S.G.) which is imperative to monitor throughout the winemaking process to keep track of fermentation. Click here for instructions with pictures on how to use a hydrometer. The steps are:
• Clean and sanitize your hydrometer.
• Put sample of wine into test jar ensuring there is enough for the hydrometer to float freely. You may also place the hydrometer directly into the primary fermenter.
• Place hydrometer in middle of jar. It may naturally want to stick to the side of the test jar, so give it a gentle tap to encourage it to move towards the middle of the jar. If you’re testing in the primary fermenter, place the hydrometer near the centre and clear away any surrounding bubbles to make it easier to read.
• With the jar or fermenter on a flat surface try to get your eyes as level as possible with the hydrometer. Note the reading at the bottom of the curve of the liquid surrounding the hydrometer. This curve is called the meniscus and the most accurate reading is given at the bottom, the same as with reading liquid in a measuring cup for baking.
• Refer to S.G. chart in your instructions to figure out where your wine is in its fermentation process.
You can test it in room temperature distilled water – the S.G. should be very close to 1.000. Click here for instructions on how to test your hydrometer.
The usual cause for a low S.G. reading on Day 1 is under-stirring. The juice base is very thick and wants to separate from the water and sink to the bottom so stir vigorously – this can also replace your workout for the day, so all the more reason to stir well! If your kit contains grape skins it is important to wait 5-6 hours before taking the S.G. Make sure to mix well before taking the reading.
There could be a few reasons for this:
• Give the fermentation time. If the room is cooler the fermentation will be slower.
• Make sure that there is no residue from cleaning/sanitizing left in the fermenter.
• Ensure that your hydrometer is reading correctly (click here for instructions on how to test your hydrometer).
Refractometers will not read accurately once fermentaion has begun.