Fly sparge - keep an inch or two over grain bed to the end?

I did my first fly sparge today and I ended up with a question. I used BeerSmith and the recipe from AHS to estimate the amount of sparge water which was about 4.75g. I rounded to near 5g and thought it would be enough to get my 6.5g for my batch. But I quickly noticed that my sparge water was running out and my collected wort was only around 3g. So my question was:

Is the objective of a fly sparge to ALWAYS cover the grain bed with water? Or do you get to a point and then let the rest of it drain? To put it another way, assuming you want to collect 6.5g, when you are done with that, do you still have an inch or two of water over the grain bed in the tun?

If you are always supposed to maintain that inch or two in the tun, then I would assume that all estimates for sparge water are too low and in reality you should just prepare an obscene amount of sparge water. In my case , I almost think that 8g of sparge water would have been about right.

Here's what I've been doing:

Maintain an inch or two of water above your grain bed until you've used your pre-determined sparge water, then let it drain completely.

Alternately, you can stop running off when you hit the appropriate ph...or hit your target boil volume.

I always use BeerSmith, and when I construct my recipes for 6 gallons, all volumes come out perfectly.

I can put more faith into the Beersmith calcs next time but when I started to see the water run out, it seemed like I had a while to go. Plus, I wasn't sure if the grain needed to be covered with water from start to finish. If so you'd obviously need a lot of water.

KMOX said:

Here's what I've been doing:

Maintain an inch or two of water above your grain bed until you've used your pre-determined sparge water, then let it drain completely.

Alternately, you can stop running off when you hit the appropriate ph...or hit your target boil volume.

I always use BeerSmith, and when I construct my recipes for 6 gallons, all volumes come out perfectly.

Click to expand...

+1 to this.

I calculate how much sparge water I will need given grain absorption and equipment losses, and then usually add about 1/2 to 1 gallon more to my HLT. This allows me to maintain 1-2 inches above the grain bed until the very end of the sparge, while not forcing me to suck the grain bed completely dry to hit my boil volume. During the last few minutes or so the top of the bed runs dry, but I dont find myself coming up short because i have that extra gallon or so of leeway.

Also, its surprising how much liquid is in your MLT even when the top of the grain bed looks dry. I did a 10 gallon batch today and I got 3.5 gallons out of my MLT after the top of the bed went dry!!