Originally Posted by adx
You cannot just toss sugar into the boil. The reaction to invert the the sucrose into fructose and glucose does not occur until the soft crack stage (265F - 275F). Since wort is mostly water you're not going to get much above 212F during the boil.
Inverted sugar syrup can be easily made by adding roughly one gram of citric acid or ascorbic acid, per kilogram of sugar. Cream of tartar (one gram per kilogram) or fresh lemon juice (10 milliliters per kilogram) may also be used. The mixture is boiled for 20 minutes, and will convert enough of the sucrose to effectively prevent crystallization, without giving a noticeably sour taste. Invert sugar syrup may also be produced without the use of acids or enzymes by thermal means alone: two parts granulated sucrose and one part water simmered for five to seven minutes will convert a modest portion to invert sugar.
If I'm wrong, that's fine, I'd just like to see a source. The reason for heating the sugar to that temperature is to reach the hard-crack stage, or rather the stage where so much moisture has been forced out of the solution that the molecules form stable bonds. But I've never heard any state that in order to invert sugar it must reach a certain temperature, only a boil which is a lot lower temperature then what is required to create hard candy. After all a sugar syrup can be inverted, isn't this what most Belgian breweries use nowadays?