Sure man, no prob... It's harder to explain than it is to do! LOL!
Ok, so lets say you do up a recipe in your favorite beer software and it includes the sugar feedings and comes in at 1.060.
But you make the recipe and don't add the sugar prior to pitching the yeast, and you take the OG reading and it's something lower than the sw predicts... Let's say it's 1.050.
So you throw some badass yeast at it and it starts fermenting, and maybe it's killing it, maybe it's not, but you would normally know when you think it's done and take the FG. In this way, you can calculate the overall apparent attenuation right?
Yup, except you gotta throw this sugar at it a couple of time during the fermentation, and it's gonna feed the yeast, and they are gonna eat it, and multiply, and eat some more... What is the real ABV? How much did it really attenuate? Who knows?
So to KNOW, you do this:
- Make recipe with sugar in software, record projected OG (again, let's say 1.060)
- Remove sugar from software, record new, lower OG (here we'll use 1.050)
- Make the beer without the sugar, measure OG, pitch yeast (let's say 1.048, pretty close)
- After 3-4 days, measure again (let's say now it's 1.028)
- Add first feeding and measure again (let's say it went up 5 points to 1.033)
==> ok, cool, that extra five points needs to be tacked onto the 1.048 you measured when you made the wort, making it 1.048+0.005=1.053
- Wait a few more days, then measure again... Now let's say it reads 1.025 (it loved the sugar and dropped seven points for example)
- Add the next feeding and measure again... Let's say it jumps to 1.030. Up 5 points again...
==> ok cool, so we had 1.048+0.005=1.053, and now we are again adding 5 points of gravity, so 1.053+0.005=1.058!
You could keep doing this if you have a third feeding, but in our example, you only have two feedings.
Ok, so the latest reading added the last 5 points to your total, making it 1.058, pretty darn close to your projected value of 1.060 but clearly more exact and based on actual readings, so this is good.
- Let it finish fermenting, and take your FG, let's say it stabilizes at 1.010
Since you started at a 'real' value of 1.058 (1.048+0.005+0.005=1.058), and ended at 1.010, you achieved 80% apparent attenuation and landed at 6.4% ABV.
SEE WHAT I MEAN, HARDER TO EXPLAIN THAN TO DO...
Anyway, each feeding adds gravity, you measure before and after to figure out how much gravity, then add that to your real original OG...
