how much molasses (percentage of grain bill) Should I add to my Baltic Porter? I want to be able to pick up on the flavor, but don’t want it to overtake the beer, and I certainly don’t want it to dry it out. Without the molasses I am thinking on OG of around 1.068 - 1.073
What type of molasses are you planning on using? I used blackstrap once years ago. Very easy to overdo it with blackstrap.
I added 8 ounces of molasses (Grandma's Unsulphured as I recall) to a 5.5 gallon Scotch Ale I made about 20 years ago, and as I recall it only became drinkable (as in enjoyable) about 5 months after bottling it. Not sure if that was solely the result of the molasses, but that's what I blamed it on at the time. https://mashmadeeasy.yolasite.com
As referenced above, it's easy to overdo molasses. Instead, I might think about using ingredients that give a molasses character instead of using actual molasses. Buckwheat honey is a good candidate for this. As is D90 syrup.
I like @EvenMoreJesus's suggestion, especially because molasses is high in iron, which you generally want to avoid in beer. That said, it's not a decisive factor—if you really want to use molasses, don't let the iron content stop you. It's just something to weigh along with the other considerations.
I have used Grandmas Original unsulphured and liked the beer. That is not blackstrap, as it it from earlier runnings in the process, and will have less minerals concentrated in it.
I once added ~75% of a bottle of Grandmas (not sure of grade) to a stout. That might have been, what, 9 oz? It was very noticeable, and not my favorite. More recently, I made candi sugar syrups, or inverts, according to instructions on the holymess website. Much less molasses in play using those instructions. I don't feel like I have exhausted all the possibilities, but I think signs point to going easy on molasses. You know, you can always add more, but it is much harder to take back.