Does lactose effect OG or FG

[beerguy1]

I was always told it did not as it was non fermentable OK I know that but, how does the hydrometer know the difference ? Not sure why this crossed my old mind but I guess I want to know. Lots of you are smarter than I so I will let you answer it

Cheers

[dick murton]

The hydrometer does not know the difference. All you are ever measuring is the gravity at that specific time - whether at time of wort collection or at the end of fermentation. Because Lactose is non fermentable, it increases the FG. Ff added before the end of fermentation, that means you need to know how much lactose in terms of degrees SG you have added, and deduct that value from the measured gravity to give the "fermented" gravity which you use to calculate the % alcohol.

[gbrower]

It is way easier to calculate everything you need with lactose(or really anything else) in plato or brix. You just need to figure out the weight of the beer and the weight of the addition.

Side note: lactose doesn't dissolve very well.