Sorghum syrup, like other sweet syrups such as maple syrup, is made by boiling sorghum sap until the sugars are thick and concentrated. The sap must be boiled for a long time, and with equipment that allows the syrup to expose a lot of surface area, which is why it is crucial for the syrup to be boiled down in a shallow, wide pan that allows water to easily evaporate.
Purchase steam-table pans from a restaurant-supply company.
Locate a spot on the property where local fire restrictions will be met when building a fire under the syrup evaporator. Typically, this will involve procuring a burn permit and locating the evaporator a certain distance from any dwelling.
Stack the concrete blocks in the form of the evaporator, as a rough-draft of how the bricks will be laid out more permanently. Make the rectangle 20 inches wide and 60 inches long, and three bricks high. Build the rectangle with one end open to allow for shoveling ashes out and building a fire within.
Re-build the concrete block formation using fireplace mortar to bond the bricks together.