Spilled Milk

I dropped a gallon of milk on my deck and it exploded everywhere. Washed it off with water but noticed a month later when it rained, it blocks some water to penetrate through like a barrier. I used deck cleaner twice, scrubbed, and sanded but pouring water over it still shows where the milk exploded.

Can I no longer stain this deck? I was going to use a darker semi-transparent stain.