A hydrometer is used to measure the thickness or density of your wine. The proper term for this measurement is called the specific gravity. You can easily make one at home from some simple parts that most people have lying around their house.
What you are going to need is a clear glass cup with water, some clay, a plastic straw, a ruler and a felt tipped marker.
Step number one is to roll the clay into a ball that is about one centimeter in diameter. You are going to want to place this clay ball on one end of your straw.
Place the device that you have made into a glass of water and hopefully it will float. If it does not float properly then you are going to want to add or remove some of the clay on the bottom of the straw. Make sure that the straw does not rest on the bottom of the glass.
Using your finger as a temporary marker you are going to want to note where the water level is and take the straw out of the water. You then need to dry the straw off and mark where the water level was with your felt tipped marker.
Make marks along the straw every one centimeter and number them. You can then use this testing instrument to check the density of your wine compared to water.
Be sure to make a fresh hydrometer every now and then because the clay that you used is going to erode away over time.
The home made hydrometer is not an exact tool. It is mainly used for comparisons between different liquids. If you want a precisely calibrated hydrometer, you are going to have to purchase one from your local brewing shop or through the links below. Once you have a professionally made hydrometer, you can also use it to calibrate your home made hydrometer into a much more precise tool