So I am trying to wrap my head around this issue. If I want to brew something like Centennial Blonde in a 23Q vessel with BIAB, calculators/calculations are showing I need 8 gallons of water to end up with 5.5 in my fermentor, to end up with 5 gallons of beer.
Why can't I just mash into the 5 gallons or even 1.25q/lb, and then add water to get it to 5 gallons of wort to boil? (very little boils off on the stove)
I mean, the amount of sugars is the same, no?
Yes! I think you are absolutely right! Although there's a minimum. With, say 10 lbs of grain at 2 qts/lb is 4 gallons. Ouch! No sparging. But dunking can make up for it. At least that's my opinion.
If you just add straight water to the boil you'll likely wind up with lower efficiency due to not doing the full-volume mash. However, if you can do some sort of sparge, say by dunking the grains in the water you want to add in, or pouring the water over the grains before adding it to the BK, you'll likely improve your efficiency beyond what you would have gotten had you done a full-volume mash.
He's doing a full-volume mash. Just not a "full-volume sparge". I think the "dunk sparging" will make up for it.
This. Because you get more sugar with a "rinse" of the grain rather than just topping off with water, your efficiency will be low. If you don't care, adjust the recipe to use more grain and cheers.
True but the question is how much water is needed for a sparge. Suppose 12 lbs of grain at 1.5 quarts a lb. That's 4 1/2 gallons for the mash. An 8 gallon pre-boil allows 3 1/2 gallons to sparge. A 5 gallon allows only 1/2. He'd have to make up by dunking.
Is there a way to calculate exactly how much more grain I would need to add to the Centennial Blonde recipe then, if I am planning on using the 23L kettle and some type of dunk sparge? Let me rephrase, I am sure there *is* but maybe I am just not seeing how to do it.
Well, you have to know how inefficient dunk sparging in less water is and no-one seems to know that.
You can experiment. Add 25% more grain (probably too much). Check your pre-boil gravity. If it's too high, you just toss out the some of the wort.
(The trick is Volume * Gravity Points = constant. This is true pre-boil, post-boil and after top off. Thus if you target o.g is 1.050 and your pre-boil 5 gallon gravity is 1.060; the 5*60 is 300, you *want* 5 * 50 is 250, so you toss out 5/6 to have 4 1/6 * 60 = 250. And top off to 5 *pre-boil* to have 5 gallons at 1.050.)
Doing no sparge or a dunk sparge probably puts you in the 65% efficiency range, just a shot-in-the-dark here.
If you have enough water it puts you in the 80 to 85% range. With not enough water... don't know.
But he can shoot low. Then if his pre-boil gravity at 5 gallons is *higher* than his targeted gravity at 5 gallons, he can ditch enough until Volume * GP = 5 * O.G gravity points.
(Gravity points, btw, are that "bits after the 1". e.g. 1.050 gravity ~ 50 gravity points. 1.035 ~ 35 points and so on.)