From a practical point of view, brewing with hay in the mash can aid formation of a filter bed. But there is definitely a flavor component as well. The first thing we do is lay down a bed of hay, then fill our mash tun and mash in with more hay combined with the malts. Then we will generally lay another layer of hay on the top of the mash which will later be sparged through. Whether the imparted characteristics survive boiling, fermentation and ageing is a valid question. But also a question that we can address by brewing and tasting. We think it adds a lovely flavour component to the beer.
