Question about sugar:

I like tea and I like to use minimally processed brown sugar as sweetener. The other day, brewing my favorite cup, I noticed I ran out of brown sugar and scrounged around and found some confectioners sugar, a bag of powered sugar. So I took a teaspoon of the stuff, it is not an artificial sweetener, just plain powered sugar. So when I put that sugar in the tea water, I noticed the stuff clumped up before it started to dissolve, unlike the granular variety which starts dissolving immediately.

Anyone know why powdered sugar would clump before dissolving? It was not wet, that is to say, the bag was not exposed to air so the sugar was fresh.

Because this reduces the interfacial energy due to the interaction between the sugar and the water surface. The interface disappears when the sugar dissolves, but this takes time.

Originally posted by KazetNagorra
Because this reduces the interfacial energy due to the interaction between the sugar and the water surface. The interface disappears when the sugar dissolves, but this takes time.

What is interfacial energy? New one on me. "This reduces", what reduces? I am thinking the surface area somehow? I would think powdered sugar would have more surface area.

Originally posted by sonhouse
What is interfacial energy? New one on me. "This reduces", what reduces? I am thinking the surface area somehow? I would think powdered sugar would have more surface area.

Yes, but the clumping reduces it.

Originally posted by sonhouse
What is interfacial energy? New one on me. "This reduces", what reduces? I am thinking the surface area somehow? I would think powdered sugar would have more surface area.

It costs energy to create a water/air-surface (mainly because surfaces reduce the relative amount of H-bridges). If all of the very small crystals of the powdered sugar would be surrounded by water, it would (temporarily) cost a lot of energy. That's why the sugar clumps together.

Originally posted by KazetNagorra
It costs energy to create a water/air-surface (mainly because surfaces reduce the relative amount of H-bridges). If all of the very small crystals of the powdered sugar would be surrounded by water, it would (temporarily) cost a lot of energy. That's why the sugar clumps together.

So is the sugar itself causing the clump or does the water drive the sugar crystals together?

Originally posted by sonhouse
So is the sugar itself causing the clump or does the water drive the sugar crystals together?

Isn't that the same thing? It's the interaction between the sugar, air and the water that causes the clumping.

Originally posted by KazetNagorra
Isn't that the same thing? It's the interaction between the sugar, air and the water that causes the clumping.

My wife threw in a curveball here: She thinks its because they mix in corn starch with the sugar. That would change the game if so. Don't know though, I though powdered sugar was just that, powdered sugar and nothing else. If there is corn starch in it, the rules would change I would think.

Originally posted by sonhouse
My wife threw in a curveball here: She thinks its because they mix in corn starch with the sugar. That would change the game if so. Don't know though, I though powdered sugar was just that, powdered sugar and nothing else. If there is corn starch in it, the rules would change I would think.

Many different kinds of finely grained powder will show similar behaviour when immersed in water.

I think powdered sugar does contain an anticaking agent, but I don't know if it's corn starch. It's possible this affects the way it dissolves in water.