Originally Posted by Paulielow
I know yeast is cheap but I'm wondering how much I
Need there's 5g under the lid but most recipes call for
You need to put all of the yeast in the beer! One packet (11gm) of Nottingham does a pretty good job on an average gravity beer. Thats 11gm of fresh dry yeast. As the yeast ages it's effectiveness diminishes quite a bit.
If you can purchase some more yeast than I would highly recommend it. I normally pitch 2 (11gm) packets of dry when I use it. You really want a lot of yeast in your beer. The more yeast you have the less they have to work to make your beer. If you don't pitch enough then they have to work harder and cannot make the best beer they can for you!
Check out mrmalty.com and his yeast calculator. The guy that put that together is quite knowledgeable.
I don't know about the lactose, adding it should give some extra body to the beer. It is not very fermentable so adding it during the boil is good. It may give your beer a little "sweetness" which I personally like in a stout. Ahhh, throw it in and if your beer is too sweet then don't add it next time!