Effects of topping off H20 during boil?

[Junket]

I use an 8.5 gallon brewpot,which i find is perfect for a 60 minute 5 gallon full boil all-grain batch, but is too small for a 90 minute boil (especially on cold, dry winter days when my evaporation rate increases). Any ideas about periodically topping off with fresh water in order to keep my volume right? I like to end up with 6 gallons of wort, but I can't get that much with a 90 minute boil. So what if I add water at 60 or 30 minutes in order to wind up with my 6 gallons? I'm not worried about my numbers being off - I'll figure that stuff out over time. I'm just wondering how this might affect the final product - carmelization, flavors, hop extraction, fermentability, etc. Any ideas?

[Speyedr]

If you're not worried about the gravity, then why worry about those other numbers? Not being a smart-ass, just saying that when you dilute like that you're going to affect the gravity more than any of those other factors. As an FYI, caramelization and fermentability will not be affected really. Hop utilization will, but as a function of gravity, just like in a partial boil (3g adding water to make 5gal) though not as extreme.

My point is that if you're not worried about the gravity, then don't worry about the rest of it either. Just calculate your recipes to 6 gal and add water as necessary.

Rob

[Eric_lovrien]

I use to do that when I was in a smaller pot (6.5 gallon). I thought I would note that becareful when adding the water as it will foam up for a minute or two.

[Levi]

I use a 7.5 gallon kettle for 5 gallon batches and I will top up with wort during the boil. I will hold back about a gallon of my first runnings and add that after half an hour of the boil. In principle I should be getting higher efficiency, better hop utilization and less caramelization this way.