I was having a bit of a sugar rush last week talking about sucrose, glucose, fructose [and ethanol]. It is physico-chemical peculiarity of the two monosaccharides that, although they have the same C6H12O6 chemical formula, they have a rather different structure and consequently rotate polarised light in opposite directions. The reason why this happens is way beyond my ability to explain.
We have a taste for sugar because, in our evolutionary past, such easily digested calories were hard to come by and those who had receptors on their tongues that recognised sugar molecules made better choices in their diet, grew a little fatter, got off with the opposite sex more often and left more offspring in succeeding generations. Their taste-insensitive cousins ate a lot of bark and wasted away. Our perception rates fruit sugar fructose highest: If sucrose tastes 100%, then fructose tastes 150% while glucose seems only 75% as good. As you know, food engineers have long been gaming the system with other peculiar chemicals - cyclamates, saccharine, aspartame - which fit the taste receptors even better than nature's intended and make us swoon with sweetie delight. The dreaded HFCS high-fructose corn syrup makes considerable in-roads to the American Maize Mountain, by processing milled corn with a frightening array of chemicals and unnatural enzymes to produce a viscous liquid called HFCS-42 which is 42% fructose. This is added to an eye-watering variety of beverages, processed foods, cereals, and baked goods.
I may get back to HFCS later, but today we are making liqueur chocolates. The ability to make something that has a liquid centre hinges on another difference in the physical chemistry of the three sugars of which we treat. Some solids will dissolve in some liquids. You know that if you've ever put sugar in your tea or made a cake or salted your porridge. Scientists are wonks for quants, so they like to measure exactly how much of solute [the solid] A will dissolve in solvent [the liquid] B. They quickly worked out that this solubility was temperature dependent: that teaspoon of sugar disappears in a flash in hot tea but requires a bit of a stir in cold water. It turns out that you can dissolve a lot of sugar in water at room temperature (20ºC) a litre L of water, weighing 1000g will take:
Fructose: 3750 g/L
Sucrose: 2040 g/L
Making cherry liqueur chocs, factory style. Similar eye-glazing choc-factory in Canada. Form your chocolate into little buckets. Fill with a suitably flavoured sugar paste - a little alcohol doesn't go amiss, but doesn't at all at all help get the sugar into solution. Then cap off with more chocolate. Voilá! You have hard candies covered in chocolate. But note in the film when they spray invertase into the filler mix of sugar and cherries. As we saw last week, invertase is the enzyme which converts each molecule of sucrose into 1 of glucose + 1 of fructose. The fructose, avid for water, goes back into solution making the interior a) sweeter b) gloopier. The glucose doesn't help on either of these food engineering axes but the average solubility [(3750+900)/2 = 2325] is more than the original sucrose-only paste. The process takes a few days at least partly because <chocolate alert> you cannot warm it up too much to speed the process along.
You can do this at home.