Place
oil in a deep pot, such as a tall 3-quart (2.8 L) pot, and heat over medium heat until shimmering. Add fennel seeds, mustard seeds, salt and red pepper flakes and heat for about 2 minutes or just until the seeds begin to pop. Add the beer, then squeeze the lemon wedges into the pot and add the lemons themselves to the pot as well. Give everything a good stir.