What is the impact on the final beer when using a yeast starter that dilutes the OG? I just brewed a Czech lager with OG of 1.057 pitching a 1 ltr starter. I had done a 2 ltr run earlier and poured off the clear used wort before a second 1 ltr vitality run up on brew day. I watched on my Tilt reading drop immediately from 1.057 down to 1.052 adding the slurry to 5gal in the fermenter. I see other brewers pouring 2 and 3 ltr flask in with not a care. So not any impact on dilution of the gravity with the spent 1.0?? Wort?
Yeast starter's impact on OG
- Thread starter Göbelbrau
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Did your Tilt rebound to a higher reading? It could be that the starter was just more at the top. Some math says that adding 32 oz (close to 1L) of water to 5 gallons of 1.057 wort would result in 5.25 gals at 1.0542. If I assume the gravity of the starter wort was 1.040, it would just change to 1.056 (though the wort would likely have fermented down below 1.010 before being added). You might get a little less alcohol production in the starter than in beer, but the with the crabtree effect, beer yeast will still produce alcohol in the presence of oxygen.
I don't worry much about adding 1L of starter into a 5 gallon batch. If I was making a 2-3 L starter, I would cold crash and decant before adding.
Adding 1 L of water to 21 L (5.5 gal) of 1.057 wort would change the SG to:
But even the above is not the correct way to figure out the starter's contribution to your "effective" OG. The "effective" OG is the OG you would get by treating the extract used to make the starter as if it had been added to the fermenter before fermenting the starter. And if you decant the starter, then you have to account for the lost volume and lost "effective" extract.
If you tell me your preferred units (gal & lb or L & kg), and what your original fermenter volume was, I can work out an example for you.
Brew on
New SG = 1 + 0.057 * 21 / 22 = 1.0544
Since your starter beer would have a higher SG than 1.000, your 1.052 reading had to be from a lower density region of the wort (due to inadequate mixing prior to sampling.)But even the above is not the correct way to figure out the starter's contribution to your "effective" OG. The "effective" OG is the OG you would get by treating the extract used to make the starter as if it had been added to the fermenter before fermenting the starter. And if you decant the starter, then you have to account for the lost volume and lost "effective" extract.
If you tell me your preferred units (gal & lb or L & kg), and what your original fermenter volume was, I can work out an example for you.
Brew on
