lactose beers finishing high, low attenuation

[oliver]

I think this is a beginner question, because I don't have a lot experience with lactose.

my last two beers both used 8oz of lactose:
1.068 -> 1.023 = 66.2% attenuation
1.068 -> 1.024 = 64.5% attenuation

My current house strain normally ferments out around 75%
Is this normal? I know the lactose is unfermentable and will read as more sugar, am I on the right track?

 

[GFHomebrew]

I think this is a beginner question, because I don't have a lot experience with lactose.

my last two beers both used 8oz of lactose:
1.068 -> 1.023 = 66.2% attenuation
1.068 -> 1.024 = 64.5% attenuation

My current house strain normally ferments out around 75%
Is this normal? I know the lactose is unfermentable and will read as more sugar, am I on the right track?

sure are because the lactose sugar stays in the brew it represents a high FG but im betting your yeast attenuated better than what your seeing using the calculator. as in the yeast ripped through most the fermentable sugars as usual but the lactose suguar is hanging around in suspension and this is what your hydrometer is reading.