I have already tried searching the home brew thread to see if anyone has tried this combination but cannot seem to find anything. Do Galaxy hops and Mosaic hops bode well together? Below are the times and hop combination for clarification. Just to clarify, where it says mash, it's supposed to be flame out.
Doing an Internet search, there are lots of recipes using both Galaxy and Mosaic. For example: https://www.brewtoad.com/recipes/galaxy-mosaic-pale-ale As for whether "mash" means flame-out, by the order of how the hops are listed, it would appear to be so. But then again, hops can also be added during the mash itself. Properly speaking, "mash" should refer to the actual mash, so this may either be a misnomer, or it actually means to add the hops during the mash. Usually, the term "Whirlpool" is used when adding hops at flame out.
Just be sure you like the hops your choosing. Otherwise keep the recipe as is. Easy enough to brew another hopper batch later.
I just kicked a keg of an IPA with Mosaic, Galaxy, and minor amount of Simcoe. It was a great beer that I will definitely make again. I used 2.5 ounces of each and 1 ounce of Simcoe for dry hopping.
