This is my 1st time using london ale wyeast and I'm a bit puzzled...The yeast was manufactured on september 8th and I made a 1.5L, 1.040 starter to boost it. It's been on a the stir plate since Friday afternoon and as of Sunday early afternoon, the og was still at 1.035 with no visible yeast clumps. All my previous starters were much quicker using different yeasts. Is london ale yeast a slow one ?