If I made a yeast starter when I brewed, will it be enough additional alcohol to need to take that into account when calculating alcohol content?
I made a 2 liter yeast starter using 7.3 oz of DME and a smackpack of yeast and fermented it for almost 24 hours.
I did an extract batch, so I only boiled 3 gallons, then I topped off to 17 liters and then pitched my yeast to make 19 liters (5 gallons).
My OG after pitching was 1.082 and my FG was 1.020. Do those measurements take into account the alcohol from the yeast starter? Or do I need to add something to my ABV calculation?
It’s not going to make that much of a difference. That said, I always finish my starter to completion, decant spent starter beer and pitch only the slurry if it is anything larger than a 1 L starter.
Agreed on both.
Me three…I also follow major’s method.
I’ll also add that even if you did add some of the spent wort it will usually be a dilution as starter worts typically range 1.020-1.030 strength to begin with.
+1
Same with whole fruit (most fruit in most beers), for the record.
I’m assuming that at the most it would only add maybe 0.1% to ABV.
Nice to know the extra little tidbit about decanting and just pitching as much yeast as possible percentage-wise.
Thanks for the quick responses. 
Right, for most beers the starter wort would lower the ABV, not raise it.
However, I also decant.
A starter should never add much alcohol to a beer. The point of a starter is to grow yeast, not produce beer. Reduced starter wort gravity and oxygen contact encourages a different metabolic pathway for the yeast which reduces alcohol production and increases yeast biomass growth.
As pointed out above, low gravities of 1.020 to 1.030 are not going to produce a good tasting end product and decanting that spent wort off the yeast cake should be an improvement to the overall taste of the beer the healthy yeast cake is pitched into.
A discrepancy to the recommendation above is that if the yeast are going into a much higher gravity wort, the starter gravity should be increased proportionally. I’d say that if the wort was more than about 40 points higher than the yeast starter wort, you might want to step the starter wort gravity up so there isn’t as much difference in the gravities.
The starter has a certain ABV, since when you add it you also increase the volume by that amount then unless the starter is a higher ABV than the beer, you will actually be diluting. Since most starters are 1.030-1.040 it is more likely to dilute than increase.
Heres an example:
A 1.030 OG 2L starter is added to a 20L batch of 1.050 OG beer. 90% of the resulting volume will be an ABV reflecting the 1.050, 10% will be 1.030. (0.9 x 50) + (0.1 x 30) = 48, the resulting 22L of beer will be an ABV reflecting an OG of 1.048.
Regarding the OG of a starter, I know the lower OGs are easier on the yeast but I think that if its too low (1.030) there wouldn’t be much cell division before the food was used up.
1.030 is what I always use and get great results. I’ve never actually counted cells, but judging by the volume of slurry there’s plenty of growth going on.
Agreed…and also a gentle environment for them to multiply in which ultimately leads to minimal stress on the yeast.
My starters range from 4-5+% (1.040-1.055) and I drink them. These are 5 gallon starters.
My starter was a 2 liter starting at 1.040. I heard that was a good concentration for a higher gravity beer since making a starter much higher could stress the yeast in the starter before they got pitched and started on the actual beer.
I had a pretty good yeast cake after 24 hours and, man, I think I got airlock bubbling within a few hours after pitching. The starter really helped for this beer given how I overshot my OG quite a bit. (thanks for the insistence of a yeast starter, Denny ).
well, since that worked for ya, here’s a bit more advice…you don’t need a higher gravity starter for a higher gravity beer. The higher the gravity, the more the yeast are stressed. The purpose of a starter is to have a good population of healthy yeast and lower gravity starters do that better. No matter what the OG of the beer I’m making, my starter gravity never goes over 1.030. It’s not that 1.040 is bad so much as that lower is better.
Sound advice Denny,
The purpose of making a starter is to make yeast, not beer.
Every now and then, OK, frequently, I get the urge to brew something truly massive, thus 5 gallons of a very flavorful, but small beer.
I Keg/bottle that beer on brew day and usually an RIS, BW, or STRONG Scotch Ale goes right on the yeast cake.
The best starter is that from a previous batch, as long as it wasn’t above 1.060 or so.
White Labs recommends a 1.040 starter. I don’t think 1.040 is a real stressful environment for a yeast, and the amount of time it takes for the sugar to be consumed is fairly short.
No. it’s not real stressful, but I feel lower is better. Tom S., any insights from a pro?
I haven’t tested it, so I can’t say for sure. Standard lab media varies in strength, most labs use between 2-5% glucose for growth, which translates to roughly 1.008 to 1.020. But research labs aren’t trying to grow as much as a brewer is, so I’m not sure it’s all that relevant. There is also very likely to be some strain dependency.
Sorry, not very helpful. :-\