Anise has a crystallization point of 59 degrees Fahrenheit (15 degrees Celsius). That’s shorts weather here in Michigan, but cold enough to crystalize full bottles of anise oil. Not to worry, simply run warm water over your bottles, or place them on a warm surface. It will take a bit of time, but the crystals will return to a liquid form. Be sure to give the bottle a good shake before opening to make sure all crystallization has broken down.