Using a converted 15.5 Gal. keg for a 1/2 barrel system is the most efficient and cost effective way to build a all -grain brewing system. The wall thickness of a keg is almost twice as thick as a ordinary brew pot, which makes it very durable, easy to weld to and modify, and it does a great job of keeping the heat in, which means that you use less propane, and mash temps stay very consistent resulting in a greater efficiency. The top and bottom of a keg are also domed, which also helps keep heat in, and a false bottom sits perfectly on the sides of the domed bottom allowing room underneath for liquid to seep out of the mash, and drain out of the kettle. This method of using a false bottom in the bottom of a keg also works great in a boil kettle situation where you would use it to strain out hops before collecting the wort. Kegs are completely smooth on the inside making them a breeze to clean. They also hold up to years of constant use, as well as misuse! Using plastic coolers to mash with is not the best idea, because the hot liquid is sitting in plastic for at least an hour. Plastic also warps and scratches easily trapping bacteria in the folds of the scratches. Beer just tastes better the less time it comes in contact with plastic. This holds true with many other foods and liquids.