So I will be doing a BIAB for the recipe I listed in the first post and it uses irish moss. I have seen a lot more people using gelatin as opposed to irish moss. Is there any significant difference?
Also, this will be my first BIAB and I am wondering how much I should be using for my starting water. I have seen a lot of people use 6.5 when doing BIAB for a 5 gal batch. Does that seem about right? Also I have seen some people sparge when doing BIAB. Should you sparge to increase your efficiency when doing BIAB if you have a way of doing that? Such as a turkey frier with the bag attached to the fry basket?
Difference between Irish moss and gelatin: Gelatin works. Irish moss doesn't always work. That's my experience.
Grains soak up 0.1 gallons per pound, so account for the amount of grains when calculating water. And then of course you'll probably be boiling off a gallon if you boil for 60-75 minutes, so add a gallon for that. Then if you want to leave any sediment behind from the grains or cold break, add a quart or two for that. You might need 6.5 gallons, might need 7 gallons -- it's all up to you and your own experience. You'll have to play around for a couple of batches to find out all your own adjustments to use.
Yes, I am an advocate for sparging with BIAB to improve efficiency. There's two ways of sparging BIAB that I have experience with:
1) The simple dunk sparge. You need a separate kettle to heat up sparge water, and then either dunk the heavy grain bag into that kettle if it's big enough (probably not) or pour the hot water into a 6-gallon bucket and dunk that way, then mix all the wort back together into the main kettle.
2) The colander/basket sparge. Still requires a second kettle for heating up sparge water. From there you essentially have to place your grain bag into the colander or basket over yet another bucket and or drain the hot sparge water over it. This method can be effective but is very very slow, and for that reason I don't do it much anymore. Dunking is easy.
With these methods and a good crush, you can achieve 85-90% or even higher efficiency. However, I'm also not an advocate for that either. Sometimes, good enough really is good enough. If your efficiency without a sparge is 75% or more, it might be best just to skip the sparge altogether, seriously. I sparge nowadays for the biggest gravity beers, but for smaller beers (<1.055 or so) I usually skip it because you can get great efficiency just from draining the bag and moving on.