I need some advice concerning freeze-drying.The problem is - I can't "get sugar glass" (in tubes 0.2-1.5 ml). If dried on a table at slightly elevated temperatures, the "pellet" looks nice and hard when probed with a pipettor tip. But if freezed in a refrigerator and put under vacuum, I get a "compressed piece of powder". I tried mannitol, sucrose, trehalose (and their mixes) to the same effect. Something seems to happen during freezing or drying, the question is - what? Being new to the field, I've read literature on the subject, but can't solve this simple problem.
I suppose it's too simple to mention in "guru's" books.
I would greatly appreciate some advice.