Here is the reply from Sarah Phillips at Baking 911 (sorry I can't get her links to work right...just cut and paste them into your browser).
"I spent some time last night doing a lot of thinking and research into your issue about Toba's Glace Icing not drying shiny. Hers is a wonderful recipe, and I am a big fan but again, the sugar crystals are probably crystallizing in the recipe. There's a lot of sugar-science going on behind the scenes with such a seemingly-simple recipe!
I have a recipe called Simple Fondant Glaze for cookies which is similar to Toba's, but will dry with a shiny gloss, because I emply slightly different heating and mixing methods. I use water instead of milk. My recipe is called SIMPLE FONDANT GLAZE and is on: http://www.baking911school.com/index_cookies.htm
I will explain what I think are the issues with Toba's recipe.
A sugar based glaze that dries cloudy means that the sugar is crystallizing and/or the sugar is not being dissolved thoroughly, just as we discussed before. Let's look at the ingredients used:
Confectioner's sugar (Powdered sugar) is a quick-dissolving sugar. But, when added to cold or even room temperature liquids, it is a known fact that sugar doesn't dissolve as thoroughly. I would think when using milk, as called for in Toba's recipe, which isn't an incorrect ingredient, that it's human nature to use it right from the fridge. My recipe includes a warming step which helps dissolve the sugar better.
Corn syrup is known as an agent that helps prevent premature crystallization of sugar. But, you need to add it when the sugar is being dissolved, not after as Toba has you do in her recipe. In mine, I have you add it in with the sugar and water.
Corn syrup will make a glaze shiny, but it won't turn a cloudy icing that has crystallized, shiny -- or, it won't correct an already crystallized glaze and make it un-cloudy. So, what you will be looking at is a cloudy mixture with a glossy surface -- but, it won't look glossy to you because of the way in which the light rays are hitting the surface of the glaze after it has dried....
If you use milk in a glaze, the fat and milk proteins will deflect light rays as it passes through the liquid. The glaze will always have a milky opalescence. Water won't give you that milky appearance, which is what I use in my recipe. The more fat you have in the milk, such as if you use heavy cream, the more the light rays are deflected. Cream has a lot of fat. Fat = thicker glaze and the glaze won't dry as hard.
Whenever corn syrup is added to a glaze mixture, it will take lomger for it to dry. In simple terms, that's because corn syrup attracts moisture and that's how it helps provide a smooth, glossy surface to a glaze. So, you have to be patient!
The important thing to remember is that Toba's recipe is NOT incorrect at all. It's just that you have to be careful with dissolving the sugar because what I think is happening is that there's a fine line between insuring that the sugar will or will not crystallize -- Another way to insure that the sugar dissolves is to let the mixture sit for 10 minutes after combining the sugar and milk and then stir and stir and stir.
There are ways to dissolve sugar in a liquid that ensure that the crystals dissolve better -- The best known technique is by warming the liquid slightly with the sugar in it plus the corn syrup, as I do in my recipe, with stirring. This helps dissolve the sugar cyrstals thoroughly! Simple sugar solutions, such as Toba's are typically made with dissolving the sugar crystals in a warm liquid: http://www.baking911.com/recipes/cakes/sugarsyrup.htm or http://www.baking911.com/recipes/cakes/syrup_simple.htm
P.S. The reason a glaze can lose its shine after 24 hours is because of the sugar crystallizing. The same thing will happen with fudge. You can have a creamy fudge, and then store it overnight, only to find that it's grainy the next day! It's because there were a few seed sugar crystals, not dissolved, that set off the whole batch to turn grainy. Also, improper storage of sugar-based recipes will cause this, but it's more than likely caused by improper cooking and mixing steps.
That's the mystery of sugar crystals.....Agitation can start the whole mixture to crystallize if there's one sugar crystal not dissolved. So, if someone used toothpicks to stir the mixture, they may not have agitated the mixture enough to set off the whole chain of crystallization.....
You must understand -- Toba's Glace Recipe won't ALWAYS turn cloudy -- And, she is NOT INCORRECT -- but, I suspect her recipe MAY have a high statistical chance of crystallizing just the way the recipe and/or mixing steps are written. Perhaps it's a complex recipe that works well for advanced cookie decorators who really know to thoroughly dissolve the sugar, to not use really cold milk, etc.
It's just like one of my butter cake recipes, I have to take another look at...the recipe is not incorrect...I may need to change a few mixing steps to ensure it has a better chance of working! It's getting mixed reviews -- it's because I need to be more specific in the mixing instructions.....There's where the art and science of writing recipes for a cookbook become so difficult! -- You can't always predict what's going to happen to a recipe once many hands get ahold of it and try it!! You can assume that bakers know what you mean, and you find out sometimes they simply don't. It's normal because a lot of baking concepts can be so difficult!
Timing and temperature are so important when making a recipe -- so in Toba's recipe, what make look like is "dissolved sugar" to Toba, may not be the same thing in someone else's eyes."
..that is such great information. I am amazed that she actaully takes the time to make such a detailed response. It's really fantastic! Thanks for sharing that with us!
WoW!! Truly helpful info there!! Thank you so much for posting this here...really does answer a lot of general 'food science' questions when it comes to this type of thing. And thanks to Sarah Phillips for being so willing to take the time to explain all of it to you and share her knowledge!! Great stuff!
This is going to be printed out and filed in my cookie recipes.
Your're the BEST!!!
Great job. The whole science of sugar is really quite fascinating. Now I feel compelled to make cookies tomorrow!
Thanks for the link...How do I get that recipe? Do I have to pay for it?
I can't get the link to work right, but if you go to www.baking911.com and go to the Ask Sarah message boards and then the Cookies section, you'll find the whole conversation.
She is still giving me more info...
I love the ALTON (science) response! Thanks for doing the homework for us Mohara! Much appreciated.
Sarah is very helpful and one smart lady...she has a PhD.