Need help with "equipment"

Good day,

A few weeks ago I created a custom equipment profile in beersmith. I wasn't 100% sure what I was doing, and I hadn't every brewed before so I filled out the profile the best I could. After finishing the profile, I created a recipe (using the standard Cincinati Pale Ale recipe described in How to Brew) with beersmith using my equipment profile. I was doing a lot of converting (imperial to metric, 5 gallon recipe to 15 liters), and because I had no previous experience with beer-making I couldn't tell if the ingredient amounts beersmith was giving me were "off" or not. I had no choice but to trust the software.

So I purchased the ingredient amounts dictated to me by beersmith and proceeded to brew. A few days later I was looking at my equipment profile again and I saw some value somewhere that I thought might be inaccurate. I refreshed the Pale Ale recipe with the new equipment profile value and suddenly the recipe is telling me that I don't have nearly enough hops to meet the style guide characteristics for a pale ale; my total IBU's for the recipe fell by 1/2. I don't remember what values I changed in the equipment profile, but I would expect that had I changed something like volume then the recipe would also be telling me that I don't have enough malt extract to hit the target starting gravity--that I need to increase my malt extract by 2. However, this is not the case, as the malt extract amounts were not affected in any way by the equipment profile change.

What I don't understand is how by changing the equipment profile I'm suddenly severely lacking in hops while the extract amounts remain fine. Also, I'd like to make sure that I've got the equipment profile filled out correctly. I have a 17 liter pot for boiling the wort. I'm putting 10 liters of boiled water into the fermenter. I'm putting 6.89 liters of water into the boiling bot, which should boil down to 5 liters. I'm adding the 5 liters of wort to 10 liters of water in the fermenter to create 15 liters of beer. How do I translate all this correctly into the equipment profile/recipe?

Thank you for your help.

Set the recipe up as an extract recipe (on the recipe design page) and set your "batch size" to what you would like to end with. Then enter "boil size"  and the volume you are actually boiling. You will get lower hop utilization when boiling less volumes. The reason is the gravity (the amount of sugars) in the boiler is high enough to reduce the amount of oils that can dissolve thus bringing your IBUs down. I would expect to use 1.5 to 2 times the hops for the same recipe when boiled at half the volume of liquid. Setting up an equipment profile can be extremely hard if your not sure of your actual values.

Read this... hope it helps!
http://www.beersmith.com/forum/index.php/topic,5140.0.html

Thank you for the reply. I didn't see the reply because the notification e-mail was in my spam box. 

Anyhow, thanks to your explanation I think I see the problem know--the boil size was probably initially set to the same value as the batch size. When I adjusted the boil size to the correct value, the necessary hop amounts changed due to lower hop utilization. I didn't know about hot utilization.

Thanks for your help.

Oh, okay. Here's a question: due to the hop utilization factor that you described (or any other factors that you can think of), would you say that one should more or less try to maximize the boil size relative to the batch size?

Yes. You will benefit greatly from what they call a "Full Boil." I try to end with at least 5.5 gallons after my boil so I try to start with 7-8 gallons or so depending on the batch and the boil length.