Effects of Pitching large yeast starter.

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Oceangrace24

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First off, normally I crash and decant my starters and then pitch the slurry. I recently brewed for the first time on my Spike Solo+ 20 gallon system and was aiming to get 11 gallons in my fermenter.
I missed some volumes and only had 10 gallons in the fermenter. This was a lager and I made a 4L starter. I didn't make the starter soon enough so I didn't really have enough time to crash it all the way and decant it.
So, I decided to pitch the entire starter. I figured this would also help me get to the 11 gallons I was shooting for in the fermenter.

My question is around the effect on gravity and ABV of the end product. Post boil, before pitching I had a OG of 1.051, which is what I expected. I Measured via digital refractometer and also my tilt hydrometer matched that.
When I pitched the starter, my gravity dropped down to around 1.044. I knew pitching the entire 4L would bring down the gravity.
If I were to use my OG of 1.051 and my FG of 1.011, I would have expected an ABV of 5.3%. If I change my OG to 1.044, it shows my ABV around 4.2%.

But here is where I am confused. I didn't add plain water to the fermenter to bring the volume up. The starter that I added was basically beer. Shouldn't my finally beer have an ABV somewhere between 4.2% and 5.3%? I have no idea what the FG or the ABV of the starter was that I pitched, but I assume it was in the 1.010-1.012 range. But it is basically beer that I added. I know it brings down the OG of the wort in the fermenter, but instead of starting with 10 gallons of 1.051 wort with 0% ABV, I am now starting with 11gallons of 1.044 wort that already has some percentage of ABV to it.

Just curious as to how this actually effects ABV since I have no real way to test and measure the actual ABV of the finished beer. This isn't a big deal in the grand scheme of things and I don't really care if my Mexican lager is 4.2%, 4.7% or 5.3%, I am just curious about the science and the process of this method.
 

Toxxyc

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What was the OG of the starter? Because it'll drop the OG of your wort, if it's been fermented. You're not pitching sugar - you are pitching alcohol, and alcohol DRASTICALLY drops the gravity reading of a hydrometer or refractometer.
 

Toxxyc

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So work out the volume of potential alcohol from your original wort, and add the volume and alcohol percentage of the starter and I'd say your beer should end up pretty damn close to 5% ABV.
 

nwhall3

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I'd say calculate the OG of the total volume given the separate OGs for different volumes:

(10G * 51 + 1.06G * 40) / 11.06G = 49.95

So your OG for the total volume would be 1.050 (rounded)
 

CascadesBrewer

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The OG of the starter was 1.040. By the time I pitched it, it would have been around 1.010 of Alcohol in the 4% range.
My understanding is that yeast do not produce alcohol during the aerobic fermentation state (in the presence of oxygen). I would not worry much about the impact on your beer, but I am not sure a well oxygenated starter, especially one on a stir plate, would contain much alcohol.
 

Toxxyc

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Yes during the aerobic phase the yeast multiplies off oxygen. But no starter will ever contain 0 alcohol. I think it has to be calculated, although I'll be honest and say I wouldn't worry about it.
 
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