Once the temperatures start dropping, the bees will have a hard time processing even the heavy sugar syrup. So I start adding bee fondant to the hives and that works pretty well for me.
A lot of people use sugar blocks, but I started making and using bee fondant after a talk by NC Master Craftsman Beekeeper Barry Harris at a Forsyth Bee meeting a few years ago. The difference between fondant and a sugar cake is that the sugar in the fondant has been inverted — breaking the sucrose molecule into glucose and fructose molecules which the bees can more readily use for energy — much like honey.
Glucose and fructose can be absorbed directly from the digestive tract of the bee without further digestive work being done. Sucrose must first be digested and converted to glucose and fructose, so it’s not as an efficient energy source.* As the bees process nectar and sugar syrup into honey, they add an enzyme that converts the complex sugars into the simple glucose and fructose sugars as well. I figure if a hive is in distress and needing the food I’m adding, having something that can be used more easily for energy makes more sense. Hence, using bee fondant instead of sugar blocks.
Note: If a hive is starving, almost any form of sugar that they can process is better than nothing.
Making fondant requires sugar, water, and an acid (I use apple cider vinegar). You will also need a thermometer because the mixture needs to be cooked at the soft ball stage (a candy thermometer works great). In addition to the sugar in the fondant, I also add some other things to give the bees a bit more nutrition. I add some Honey B Healthy and substitute pollen to the slightly cooled syrup.
If you search for bee fondant, you will find a number of recipes and videos. You can also just buy fondant from most bee supply companies. The fondant sold and many of the videos use corn syrup in their recipe to make it more pliable and to keep it from crystalizing so fast. If you use corn syrup, you can use a standing mixer to beat the syrup without it starting to set up on you so fast and creating a mess. I prefer to not use corn syrup and my bees have no problem with the crystallized form of fondant.
I pour the completed fondant into shallow aluminum pie pans. They stack easily for transporting, the fondant comes out easily, and the fondant is thin enough to fit on top of the top bars of the hive with just a 1 or 2 inch shim. I put a piece of waxed paper with slits cut in it down first and then put the fondant on top of that. Extras can be frozen for later use. The bees seem to like it.
As an experiment last year, I made a deep frame of fondant using 1/2 inch wire mesh and waxed paper (plus tape and staples). The bees ate it.
*Reference: Honey Bee Biology and Beekeeping by Dewey M. Caron with Lawrence John Connor