Are you sure you haven't got the two batches mixed up. 75% attenuation with Windsor (1.076 to 1.018) is probably the highest I have ever heard of with Windsor; more typically it is low to mid 60s.
63% attenuation with 1728 is low; that yeast specs out at 69 to 73%, and has no real temperature issues (works down to 55F).
If one has done better than the other and you want to bring the higher FG down more, I would recommend racking the higher FG beer onto the cake of the lower one.
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