viable yeast cake

I have a yeast cake that I planned to wash and save. Its been sitting in the primary fermenter, still closed and airlocked for about a month. I peeked in it tonight and it looks and smells yeasty with no mold or anything like that. Is it still ok to pitch a second batch on top of?

Yeast viability after a month has decreased quite a bit, depending on the type of yeast you have. Wheat beer yeasts degrade rapidly where something like a Cal ale yeast lasts longer. If you don't smell any autolysis (burnt rubber) or off flavors it should be OK. If you wash the yeast, make a starter and repitch it should be fine. It also depends what type of beer the cake was from. If it's a high gravity beer the yeast cake may be too stressed.

it was a low gravity 5% or so newcastle clone. Whitbread Ale (Wyeast Labs #1099). I just hate Having to buy it again. I think its fine in terms of mold etc ... I just would hate to waste a batch of wort by dumping it on an old dead yeast cake. I have heard of others doing that I just dont know what the shelf life is of the old yeast.

try to wash it sooner next time, and throw it in the fridge.

Definatley make a starter to proof it before pitching it into another batch.

When i reuse yeast cakes, I usually plan to simply pitch the next batch as soon as i rack off the cake.

Wash and a starter and I think you'll be fine. Next time I would wash earlier.