How to account for gravity of yeast starter

[scottatdrake]

Hi, all. Ran into an unexpected snag today and wanted to hear what you think.

I brewed this Christmas Ale and had hit all the numbers right up until I added my yeast starter.

I was right at my 1.073 OG post-boil goal but then added my 3.25 quart starter that had a gravity of 1.040 (per Mr. Malty). When I measured the combined gravity just before snapping the lid on the bucket, it had dropped all the way down to 1.060 or so. Ooops.

So my question is, how do you account for the gravity and volume of a large-ish starter in the gravity of the entire batch? I assume BeerSmith has a way to account for this but I can't figure it out.

 

[windbreaker123]

Did you decant or just pour 3.25 quarts in. And did you stir after pitching ?

 

[Golddiggie]

I decant the spent wort off of the yeast in my starters, since they're all done by the time I'm ready to use them (~24 hours with the stir plate)... Means I'm pitching a nice and thick yeast slurry into primary. Typically <16oz of slurry goes into my primary.

If you decant the spent starter wort off of the yeast cake in the starter, you won't have this issue... Also, using a stir plate means you get to make smaller starters, that finish faster, than without one. When you factor in the cost of DME (in my area, the LHBS sells it for about $6/1# bag) the stir plate pays for itself pretty fast (depending on how often you brew)...

BTW, for the brew you just made, using a stir plate, you could have made a 1.3L starter (with liquid yeast) and had enough yeast cells going in. Mr. Malty calls for about 3.5L starter without the stir plate.

 

[windbreaker123]

^1 What did you pitch in this batch ? 3.25 quarts of starter or did you decant ? My simple and dickhead answer would be. Screw it you took the og after pitching 3.25 starter and your og was 1.060. Live with it and learn.

 

[PoppinCaps]

To answer the OP, no I don't think BeerSmith has a way to calculate this. You've basically offset the gravity of the wort by displacing with a volume (14%) of very low gravity. If you do the math, roughly estimated the final OG (ha) should be around 1.062. I doubt it will do much to the beer if the starter was fairly neutral, since any alcohol made in the starter will be in your beer.

Yeah, like they said, cold crash the starter and decant the liquid off before pitching...

 

[Yooper]

Well, it can be figured with some simple math. 1.073 at 5? gallons. Plus, you added 3.25 quarts of beer. The issue here would be what the FG of the spent wort was- probably about 1.010 or so but if you didn't check it you don't know. But say the OG was 1.040, typical for most starters. And guess that the FG is 1.010. That would be adding 3.25 quarts of 3.9% beer to your wort.

As was mentioned, in any starter bigger than a pint or two, make sure you chill and decent the spent wort. It's hopless, oxidized beer, and nearly a gallon may very well have a flavor impact.

 

[ajf]

I think the real problem is that you didn't mix the starter adequately before taking a gravity reading after adding the starter. Your 1.060 reading is low due to inadequate mixing.

-a.

 

[scottatdrake]

No, I did not decant and did not use a stir plate. I see how both of those things would help. (I've been looking for an excuse to get a stir plate anyway.) Thanks for your help.

 

[Bensiff]

I think it is pretty well covered, but crash cool your starter, decant, slowly warm to pitching temp and then pitch (I crash the night before, decant before beginning to brew, and let that sit on the counter while brewing so its ready to go. But think about what you did...assuming this is a 5 gallon batch, you added 3.25 qts of starter to it, that means your beer is around 15% starter, do you want your beer to be comprised of 15% starter? Just something to think about next go around.