I've got a batch of dark muscovado sugar that I rarely use, sitting in an airtight ziploc bag. Upon opening it today, I noticed that is gone very hard and some of the lumps are white inside. There's also a few darker ones.
Is this natural for this kind of sugar or has something happened to it (could be a fungus for all I know)?
Muscovado sugar is a partially refined sugar. Hence, it has a lot of what is essentially molasses contained in it. The molasses can migrate, leaving whiter areas; also scraping with a spoon, e.g., can leave whiter areas.
To reconsitute, place in a jar with a piece of bread or covered with a damp cloth (what I do). Within a few hours, it should be nice and soft as sugar is quite hygroscopic. If you use bread, it (the bread) will probably be hard.
