Ume plum vinegar is a kind of vinegar made from ume plums, a Japanese plum. It is typically used as a condiment or seasoning in Japanese cuisine.  Ume plum vinegar is also popular in other East Asian countries, such as China and South Korea. It doesn't need to be frozen, but it will keep for a very long time if you put it in the fridge.  The vinegar may get cloudy when cold; this is normal. If you warm up the bottle by leaving it in hot water, the consistency will change back to its original state.  If refrigerated, it can last up to about a year.