Belgian rock sugar is beet sugar that is brought to ‘crack’ temps and allowed to cool, which results in it becoming hard. Liquid Candi sugar is inverted. The color depends on how long it’s boiled. Invert sugar is chemically similar to honey without the nuances. Here is a quote from Randy Mosher on the subject:
“There is a tremendous amount of confusion on this subject among us
homebrewers right now. I think a lot of the problem is related to the
translation difficulties, and Belgian and American brewers assuming each
knows what the other is talking about.
Having just done the tech edit on Stan Heironymous' new book, Monk Brews,
this subject came up a number of times, and I think we finally got it
pounded into submission. Here goes.
"Candi" sugar may refer both to rock candy (which is what we Americans tend
to think it is) but also to a cooked liquid caramel syrup. In my experience,
this is more often to be case when a Belgian is talking. On old Belgian
labels and in brewing books, candi sugar invariably refers to the caramel
syrup. Properly made, this is a class III caramel and is made from invert
sugar combined with ammonium carbonate or similar source of nitrogen. The
rock candy is definitely not inverted, as invert sugar won't crystallize.
The two are not interchangeable. Caramel syrup has a considerable amount of
both color and flavor, and the flavors are of a distinctly rich caramelly
kind, quite different from semi-refined sugar. Here's a link to the Web site
of a sugar company in Belgium that sells both:
The white rock candy is a waste of money. Sure, it's shiny and cool, but it
is identical in chemical composition to grocery store sugar. Cane or beet
does not matter--the molecules are the same (although your grocery store
probably has beet sugar if it makes you feel better). In Belgium, the rock
candy is not so expensive, which is why it's used. Jeff Sparrow (Wild Brews)
says the Belgian brewers laughed out loud when he told them how much we were
paying for the rock sugar.
I tried a little experiment and ground up some of the white, pale and "dark"
rock candy, and tried to tell the difference. The white and pale (yellowish)
ones were absolutely identical, and I think I might have been able to detect
the slightest hint of character in the "dark." I plan on getting this blind
in front of some judges and see what results I get.
For most brewing purposes, I prefer turbinado or similar semi-refined sugar,
or ethnic "concrete" sugars like piloncillo, jaggery and others. These were
widely used in brewing in England, Belgium and France less than a century
ago, so they're not such a bad fit with tradition.
Now, yeast will create invertase and make glucose and fructose (invert).
Sorry about the long post. But, bottom line... use table sugar if you are simply using blonde rock or liquid candi sugar to up ABV.