Impact of Boil Size

In looking at Papazian's recipes in Joy, I see he has several different boil sizes for different recipes. For example, the Itsok Kolsch boil is quite low in size (1.5 gallon into 3.5 cold water) while others are 2.5 gallon. So, when I do this recipe, does it matter if I go with his 1.5 gallon boil size instead of, let's say 2.5 gallon (and pour into 2.5 gallon cold)? What is the impact on adjusting the size of the boil, is it significant or insignificant in this particular batch size (5 gallon)?

The only thing I'm aware of it affecting is steeping specialty grains. For example, if your steeping Crystal 120L in 1.5 gallons of water you'll get a lot less of its color and flavor that if you boil the same amount in 4 gallons of water.

Your hop utilization will also be affected. More water gives you more IBUs from your hops. Beersmith or other brewing softwares should help you find the impact easily.

As far as significance, I don't have beersmith in front of me, but have seen changes in boil size that require pulling out 1 oz of hops to keep the IBUs down where the recipe specified.

I'm a total newbie, but was wondering the same thing for my last brew.

This is what I gathered, which hopefully, is all true.

For a specific recipe, use the original water volume to steep the specialty grains. This is what will dictate the flavors and colors that are leeched from the grain. Then, if doing a full boil, put in the rest of the water and bring to a boil. (add water for boil off, about 1.3 gallons per hourish for me) Add extract. You then want to adjust your Bittering hops for the water volume. The hop utilization changes with more water. The full boil will also reduce the caramelization of the extract that cause darker colors and caramelized flavors.

I guess I will follow a recipe when I have it, thing is, many do not really address it.

I'd say the most important thing is to take good notes. I record what size brew pot I use whenever I make a batch, along with boil time, ingredients, outside temperature, humidity, and anything else that happens that might be different next time.

This way you can always go back and find contamination sources, or find what made a particular batch extra tasty. You might find that the smaller pot turns your recipe into something that tastes great for you.

I've seen several extract recipes that do not list the boil size. Sometimes its listed in the fine print. If you're looking at an all-grain recipe, obviously it's a full boil. You usually have all the water you need (if not much more) by time you're done mashing. If you take good notes, you start to modify these recipes, and can include all things on your personalized recipe (such as boil volume).

If you're going for an exact clone, probably use the boil size listed, but still take good notes. Enough rambling. The most important thing is that you don't forget to RDWHAHB!