Should I Add More Yeast?

[nbrack]

Yesterday I brewed my first full boil 5-gallon batch of beer. It was an extract Russian Imperial Stout with a target OG of 1.076 to 1.080 (I think). I came in at 1.071 which I think was pretty good, as I ended up with 5.75 gallons going into the fermenter.

My question has to do with the amount of yeast that should be used. This kit came with a dry packet of Safale S-04. I re-hydrated it in 95 degree water for about 25 minutes while my wort was chilling. I am worried that the one packet of yeast may be too small of an amount for a beer at this gravity... would it be a good idea to pick up another packet and pitch it into the fermenter tonight?

 

[Pie_Man]

First, I suspect your gravity was slightly lower because you had extra volume (5.75 gallons). Basically, the same amount of sugar, but more diluted.

To determine yeast pitching rates, I'd recommend you use mrmalty.com or yeastcalc.com. According to mrmalty, about 1.5 11g packets are needed for this beer. If you're going to add more yeast, I'd do it soon before too much alcohol is created.

 

[nbrack]

Thanks for the reply!

I pitched last night about 5:00 pm. If I pitched another 1/2 packet tonight at 5:00 pm do you think that would be quick enough?

On a side note, the wort taste fantastic!

 

[Pie_Man]

That should be fine.

 

[beerman0001]

If fermentation has already started adding more yeast is a waste.

 

[weirdboy]

It is much too late to pitch more yeast now.


You ought to be fine, although I suspect that by using S-04 and slightly underpitching, you're going to get a pretty fruity nose on the beer.

 

[Pie_Man]

I'm confused why it's too late to add more yeast after only 24 hours? I've seen recipes that use blended yeast strains were one type of yeast is pitched after the wort cools and then a different yeast is added once active fermentation begins (most recently I saw this technique mentioned in the Oct. 2012 issue of BYO when discussing a Belgian IPA). I wouldn't think 24 hours is too far off from the beginning of active fermentation, but I could be wrong.

I have only one experience with adding a second addition of yeast. One of my first beers was supposed to be a barley wine that had a stuck fermentation, so I added a vial of white lab's high gravity strain after two weeks in the fermenter. It did work to reduce the gravity by a few extra points, but I learned my lesson about under attenuation at that point as the beer never reached the FG I was looking for. Now, I make sure to pitch the correct amount of yeast and my beers have certainly improved.

 

[weirdboy]

Because of the yeast life cycle. There is typically a short "lag" phase before the yeast start growing exponentially, but once you get past 24-36 hours or so, the yeast have pretty much multiplied as much as necessary to in order to get the job done. Pitching another vial or packet of yeast at this point (especially of the same yeast strain) isn't really going to accomplish anything useful...you've already missed your chance to avoid the phase where most of the off-flavors are produced due to low pitching rates.



Blended yeast strains are a whole different ballgame. The reason you are pitching multiple strains is to deliberately develop flavors and aromas associated with the individual strains. I will also note that in many cases with blends, you are taking advantage of one strain's ability to process different sugars that one of the other strains cannot. e.g. pitching a brettanomyces strain after primary...the brett can break down sugars that saccharomyces cannot.

 

[Pie_Man]

Great explanation weirdboy, thanks.

I'll add that my motive for advocating more yeast at this point was not to avoid off flavors in the lag phase, but to avoid the beer being underattenuated and perhaps cloying and overly sweet from the residual sugars. While other factors like fermentation temperature, aeration, and the amout of unfermentables also factor into a beer's attenuation, in this case it seemed like too much under pitching; 11.5g vs. about 16-17g of dry yeast that should have been pitched according to mrmalty, nearly a 50% increase to what was originally pitched.

I'll add that adding yeast at this stage certainly has some difficulties and will probably not be as effective if the yeast were added initially. The oxygen levels, alcohol, probably some other factors could all inhibit the newly added yeast from doing their job.

 

[nbrack]

Alright I decided not to add anything and just let it be.

Sorry to vent, but its a little frustrating that the kit makers wouldn't mention this or supply another packet with the kit! But I guess then there may be problems with people over pitching by adding two full packs?

 

[weirdboy]

Not so much.

It is a very common practice for kits to come with less yeast that you'd typically want to pitch, in particular for the higher gravity styles like IPA, Imperial Stout, etc. For dry yeast in these styles, I typically pitch two packets. For any beer I make greater than about 1.045 OG, I usually make a starter wort for liquid yeast. That's assuming 5 gallon batches, of course...for smaller batches or lower gravity beers, a single vial/smack pack is usually fine.