Belgian brewers use candi syrup, a byproduct of beet sugar production, in their beers to impart caramel and melanoidin flavors either in conjunction with or in place of character malts. It’s available here at homebrew supply stores but is fairly expensive. But it’s cheap and easy to make. Here’s one way:
In a heavy saucepan, heat 1 pound cane sugar, 2 cups water and 1/4 tsp citric acid, the canning kind, to a boil, stirring to dissolve the sugar. Continue heating over medium high heat and monitor temperature with a candy thermometer. The temperature will rise slowly through about 240 degrees, then will begin to rise quickly. Reduce heat and hold between 280 and 295 degrees. The mixture will begin to darken through amber to dark red, the aroma will start as buttery, then rum, then dark rum and raisins, drop samples on aluminum foil to cool to allow you to monitor color and flavor. By keeping the temperatures under 295 degrees, you will avoid charred flavors. When the mixture is dark enough, turn off the heat and cautiously add 1/2 cup water, stirring, to create a syrup. Alternately, pour the mixture onto aluminum foil in a pie pan to cool and solidify.
You can get a fruity effect using a nitrogen source – I tried DAP/Urea based yeast nutrient. The result was, as mentioned, much fruiter, sweeter, less char although the same notes were there. So if you want the rum-burnt sugar notes, no DAP, if you want raisiny-fruity, use the DAP. Between a half tsp and a tsp should be good. Note you will smell ammonia as this cooks….
Store the syrup in a cool, dry place until needed. Taste it – the flavors are intense! One to two pounds of sugar made into syrup should be enough for a five-gallon batch. If you want to determine the contribution of the syrup, dissolve an ounce of it in a cup of water and take a gravity reading. The last two digits are the contribution in point-pounds per gallon (PPG), assuming you are reading three digits right of the decimal on your hydrometer.