Dissolve yeast in the water or beer. Whisk in sugar and salt. Mix in bread flour. Knead for 5 minutes. Form into a ball, put into a greased bowl and allow to rise for one hour. Roll dough out into a 13 x 9 rectangle. Cut into 8 lengthwise strips. Wrap one strip around each brat.
Bring 5 c. water and baking soda to a boil. Drop wrapped brat into the boiling water fro 30 seconds. Place brat onto a greased baking sheet. Mix egg yolk and water. Brush onto the dough covered brat. Sprinkle with salt. Do this for all remaining brats. Place baking sheet with brats into a 425 degree oven for 15-20 minutes. Serve with mustard.