I'm a little new to using Brewer's Friend and this is my first post, although I have been brewing for about 4 years. My likes are high ABV ales and stouts. Unitl Brewer's Friend, I had no idea that my efficiency was areound 50%. All I knew was that I wasn't hitting my target OGs at pitch time or getting the wort volume I was expecting. This past brew I calculated too much water and as a result my pre-boil gravity was too low according to the calculator but that was guessing at the total wort volume while still mashing. After sparging and getting ready to boil I found I had missed my 12-1/2G target by an additional 5-1/2G. Yea, that much. No too funny when it took 6 hours to mash and sparge just to get the gravity where I was satisfied. I then proceeded to boil it down to my 12-3/4G before adding my hops and other ingredients. After the final hour of boiling I was at 11-1/2G. After cooling I was pleasantly surprised that my OG of 1.104 was only a few points off my target at 75% efficiency. I contribute the added water and added mash/sparge to my OG. Here's the question, what effect does 4 hours of a slow rolling boil do to the wort? Will my flavors be off?