Two carbohydrates, an alcohol, and an acid walk into a bar. The carbohydrates are holding hands, but the acid wants none of it. She breaks them up with hot water in their face and a punch in the gut, then scrams. The skinny alcohol, seeing her chance, gets right between them before they can reconnect.
and there you have it — you’ve just created starch glass!
The starch is very very long chains of carbohydrate which normally crystallize to opaqueness. These can be broken (hydrolyzed) by strong acid, in this case white vinegar whose active ingredient is acetic acid. The heat really helps to get the molecules moving and so makes the acid work much faster than it would at room temperature. The heat can actually help water molecules to similarly break up the starch. The glycerol prevents the shortened starch molecules from just recrystallizing again after all the water and acid are boiled off. The glycerol gets physically entrapped between the starch molecules (intercalation). The broken-up starch chains can no longer organize into an opaque solid; they can no longer crystallize. This new highly disorganized, solid arrangement of moderately long molecules becomes translucent and is called a glass.