Calculating OG and FG with lactose

[frozt]

Hello all,
Looking at recipes for milk stouts at the moment and I'm having some difficulty calculating OG and FG properly when lactose is involved. The wiki says that lactose is partially fermentable, while members in posts on this forum have stated that it is completely unfermentable. I saw a post mentioning that 1 lb. of unfermentables adds 9 PPG to the FG. Beersmith's grain reference says lactose is 35 PPG. Do I calculate PPG as usual with lactose or is it a percentage of the stated PPG? Also, does the FG raise 9 PPG per pound for lactose or less if it is only partially fermentable?

Thanks

 

[Nanobru]

Lactose is considered to be unfermentable. One pound in one gallon of water yields an OG of 1.030. One pound in 5 gallons of water yields an OG of 1.006. If you were to use one pound in a five gallon batch, it would raise your final gravity by .006. Ex: you brew a stout with a final gravity of 1.016 (with out the lactose). If you were to add the lactose, because it is unfermentable, the FG would now be 1.022. Even for those who say lactose is partially fermentable, the difference in calculation would be unnoticable.

 

[frozt]

That makes sense, thanks! Just curious though, where did you find the PPG of lactose to be 1.030? Beersmith says it's 1.035?