I have been baking challah bread for sometime, tinkering with a variety of recipes.  I have been using instant yeast, starting with a slurry (2.5 tsp. of yeast, 1/2 cup flour, 1/2 cup water, let rise for ten minutes until batter gets puffy) and then adding the slurry to the liquid ingredients, and then adding flour.  The challah is sweet; it contains both sugar and honey (and vanilla) (and another 3/4 cups of water, and some salt). 

While the results are good, it takes a good 3-4 hours to double in size during the first rise.  Any thoughts why this takes so long?

Thanks.

 Jack