Why Not to Pitch On Your Yeast Cake - Page 5

Bob · 03-04-2010, 03:10 PM

Thanks, guys. I just got sick of writing the same thing in a dozen different threads. Figured I'd put it in one central location.

Cheers!

Bob

**Bobby_M** · 03-04-2010, 03:27 PM

Quote:

Originally Posted by Bob

Attenuation is, to the best of my knowledge, not affected by over-pitching. In other words, pitching more than the required amount of yeast will not increase attenuation. There are many factors at work in attenuation, more than simply a surplus of yeast will accommodate.

The ability of the particular strain to metabolize different sugars, and the presence of sugars in the wort (accessible to yeast) are more important than how many cells are present. In other words, if you have a surplus of sugars which your yeast cannot metabolize, no increase in colony size will attenuate those sugars. For example, you could put five pounds of slurry in a 5-gallon batch of beer rich with lactose and no real difference in attenuation would be seen.

Attenuation can be adversely affected by underpitching; the literature is clear on that issue.

Make sense?

Bob

I agree with this post but I do have experiment results that confuses the issue for me. Four samples pitched with dry yeast at recommended rates following both dry pitch and rehydration as well as O2 injection vs. none all ended up with FG = 1.014 and what I was expecting. The control sample pitched at 14x recommended rates ended up FG = 1.010.

The "recommend" rate was .5 grams per 1/2 gallon wort as calculated from a recommended pitch of 11grams for 5 gallons. Were the samples underpitched or does a gross overpitch really attenuate more?

jmo88 · 03-04-2010, 03:40 PM

Quote:

Originally Posted by Bobby_M

I agree with this post but I do have experiment results that confuses the issue for me. Four samples pitched with dry yeast at recommended rates following both dry pitch and rehydration as well as O2 injection vs. none all ended up with FG = 1.014 and what I was expecting. The control sample pitched at 14x recommended rates ended up FG = 1.010.

The "recommend" rate was .5 grams per 1/2 gallon wort as calculated from a recommended pitch of 11grams for 5 gallons. Were the samples underpitched or does a gross overpitch really attenuate more?

How did the overpitched sample taste?

**Bobby_M** · 03-04-2010, 03:55 PM

I have to find my tasting notes to be sure but I'm pretty sure it was the most "clean" one of the five samples just as you'd expect.

SpanishCastleAle · 03-04-2010, 04:38 PM

Good write-up Bob. Kaiser did some experimenting with this and made a thread about it (too lazy to look it up...not too lazy to wash my cakes and pitch a measured amount from them

). IIRC, his experiment was inconclusive but as I recall he found contradictory info on it (like Denny posted earlier itt). His research led him to believe that homebrewers and pros were on opposite ends of the spectrum (i.e. homebrewers often believe under-pitching increases esters but the pros believe over-pitching increases esters).

Another thing I don't like about over pitching onto a cake is that you had all that extra yeast that could have been saved for another batch.

Lastly, I can't remember where I read it but I thought I read that the final cell count in a batch of beer made from wort of a given gravity/composition was fairly constant regardless of pitch rate (unless way too low). IOW, the yeast only multiply to a certain count and the original pitch rate determines how much growth that needs to occur to hit that count. That might help explain why it doesn't really affect attenuation unless you way underpitch. BTW, I don't think what I just wrote is inconsistent with Berrriffic's earlier post where he said:

Quote:

Yeast tend to replicate 3-5 times from the correct pitching number to the final number in the beer.

Due to the bolded word.

EDIT: Here's Kaiser's experiment from his BrauKaiser page but the thread he made here had some good discussion. HBT Search is not working for me so I can't look it up.

EDIT2: Found a thread on it here. On the first page of that thread I provided a link to some of the other threads I mentioned above.

**nutty_gnome** · 03-04-2010, 04:51 PM

I would like some clarification to make this information applicable in practice.
I wash yeast. After I wash, I get what is essentially a cylinder of creamy tan yeast at the bottom of my jar. I can calculate the volume of a cylinder and find out how many milliliters of washed yeast cake I have.

What I want to know is: If in our 12 plato, 5 gallon example, I was supposed to pitch 228ml of slurry, can I get the same results by pitching a washed yeast cake that is 1/4 that volume (in this example 57ml of washed yeast cake). Or did I misunderstand the satement in the thread that a cake contains 4 times more yeast by volume than a slurry?

This information would help me to know what size jars to wash yeast into so I could gauge how much I'm pitching. N_G

**conpewter** · 03-04-2010, 04:53 PM

Might be useful to weight the carboy before making your "Starter beer" of a normal gravity, then when you rack off that and are ready to put your big beer on it, you can weigh it again and determine how much yeast slurry is there and if you need to pour any of it off.

BioBeing · 03-04-2010, 04:54 PM

Quote:

Originally Posted by Denny

OK, no argument, but some discussion, OK? You say "When you over-pitch the colony doesn't need to reproduce. Thus measurably fewer esters are produced." Dr. Clayton Cone of Lallemand says pretty much the opposite...."ester production is related to yeast growth but not in the way you might think. The key element to yeast growth and ester production is acyl Co-A. It is necessary for both yeast growth and ester production. When it is busy with yeast growth, during the early part of the fermentation, it is not available for ester production. Ester production is directly related to biomass production. Everything that increases biomass production (intensive aeration, sufficient amount of unsaturated fatty acids, stirring) decreases ester production. The more biomass that is produced the more Co-enzyme A is used and therefore not available for ester production. Anything that inhibits or slows down yeast growth usually causes an increase in ester production: low nutrient, low O2." The full article is at http://www.danstaryeast.com/library/yeast-growth. Care to comment?

I had an issue with this, based on what I know about coenzyme A from studying lipid synthesis in other systems. Acetyl-CoA levels in most systems do not vary much in different growth states. This apparently holds true for yeast too [Yoshioka and Hashimoto (1984) Agric. Biol. Chem. 48; 207-209].

In delving a bit deeper, acetyl-CoA, acyl-CoAs and fusel alcohols are required to make the flavor active acetate esters. The enzymes that put these together are called ester synthases, the major one being ATF1. The transcription of the gene encoding ATF1 appears to be key step in the process, and is regulated in a complex manner: it is inhibited by oxygen and unsaturated fatty acids; and activated by fermentable sugars and nitrogen. Anything that affects the activity of these synthases will affect the ester formation.

Here is a review I am plodding through... Flavor-active esters: adding fruitiness to beer. Let me know if you cannot get the pdf They are talking about this mainly in the context of high gravity lagers, that get diluted prior to packaging, which is apparently how most lagers are commercially made! High gravity worts lead to increased ester production, although addition of maltose instead of glucose can diminish this effect. All very complicated!

Denny · 03-04-2010, 04:55 PM

Quote:

Originally Posted by 2bluewagons

Wondering if the practice of using yeast cake in the event of stuck fermentation has a place here?

See thread: http://www.homebrewtalk.com/f13/psa-foolproof-stuck-ferment-fixer-72072/

As Evan! says in this thread, despite best practices in proper yeast pitching, sometimes the FG isn't as low as one would like. When pitching a beer that is 80-90% fermented onto a cake, I would think that disadvantages discussed when using the cake as a primary fermentation method would be minimized?

Hope this qualifies as discussion, not disagreement.

I agree with you. In that case, since you're not aerating the beer to encourage yeast growth, you need to use as much yeast as you can.

BioBeing · 03-04-2010, 05:28 PM

Bit more reading... Acetate esters mentioned above are only one form of volatile ester that contribute to flavour. The next class are the ethyl esters.

Acetate esters: (in which the acid group is acetate and the alcohol group is ethanol or a complex alcohol derived from amino acid metabolism)

ethyl acetate (solvent like aroma),
isoamyl acetate (banana aroma),
phenyl ethyl acetate (roses, honey).

Ethyl esters (in which the alcohol group is ethanol and the acid group is a medium-chain fatty acid [MCFA])

ethyl hexanoate (anise seed, applelike aroma),
ethyl octanoate (sour apple aroma)
ethyl decanoate (floral odor).

Ethyl ester production appears to be a bit less studied, but seems primarily depended on the amount of medium chain fatty acids present. Ethyl esters tend to follow the same pattern as acetate esters, except they do not change with the sugar content of the wort and adding unsaturated fatty acids leads to a decrease in ethyl ester production. Increasing the temp of the fermentation increases the amount of acetate esters more than ethyl esters. In fact, ethyl hexanoate levels hardly change between 20 and 26*C.