I'm with sdxj and gsbb on this. Times and temps. If you mash at lower temps (148°-152°), you will get more fermentables. If you mash above 158°F, you will have nothing but non-fermentable sugars that will leave you with a ridiculously high FG. So, it may not have been a yeast issue in the first place. Depending on style, land between 148° and 158°. Or, mash low with most of your water and sparge high (170°) with a gallon or two.
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