The German soldiers appear to be "cooking" sauerkraut from fresh cabbages. Sauerkraut is fermented with salt in barrels over several weeks, until acetic acid develops.
While characters Abraham and Richard Woodhull are at the harbor in New York, the ships in the harbor are flying the current version of the British Union Flag, which did not come into use until 1801. In addition, the incorrect flag that actually is being flown is hoisted upside down.
As Caleb rows away from the dock, he taunts the British soldiers by singing "Farewell Spanish Ladies." This song was written during the Napoleonic Wars, years after the American Revolution.