When making homebrew you need to make sure that the liquid is at the right temperature. If it's not the ingredients will not work together as intended. Constant monitoring of the temperature is essential so you will need a thermometer.
In those winter months it can be difficult to keep your brew at a constant temperature. As it gets colder you may find the need to warm the liquid up with a brew belt. These can help regulate the temperature of the brew when it's too cold to work on its own.