Yeast starters and oxidation/off flavors.

[Schnitzengiggle]

Alright I have made starters for a while now, and recently have begun using a stirplate. It has been my practice to pitch the entire starter into my wort, however, after pondering the subject and doing a little research I am curious to know how everyone else feels on this topic.

Please correct me if I have misunderstood anything.

First of all, when making a starter, overpitching is occuring. For example, pitching 1 WL Vial, or 1 Wyeast Activator into 1 liter of ~1.040 wort is definitely overpitching. Since overpitching (as well as underpitching) causes off flavors, I will assume that off-flavors due to over-pitching are definite in a starter.

Secondly, if the starter is being shaken intermittently, or constantly stirred with a stirplate, I am assuming oxidation is occuring. Since oxidation is another source of off-flavors I would imagine that oxidation is qualified.

Thirdly, starters may be grown in temperatures that exceed optimum fermentation ranges. Since we are growing yeast (which like warmth) and not necessarily making good beer with a starter, this also will lend off-flavors.

Fourth, pitching a starter at high krauesen has the yeast prepared to ferment, however, you cannot pitch at high krauesn if chilling and decanting. As discussed, if there are any off-flavors, they will be going into the wort.

Last point would be, glycogen reserves. If pitching at high krauesen, the yeast are ready to go. If fermentation has fully attenuated, chilling, decanting, and pitching slurry provides the yeast with a glycogen reserve which readies them for a new fermentation. It is my understanding that glycogen reserves help make more healthy yeast.

Having said that, to the actual questions.

1. If the opportunity to pitch at high krauesen passes, and chilling and decanting conflicts with a brewing schedule, is there a plausability for off-flavors to transpire due to an oxidized, warmer than fermentation temperature starter?
(due to all of the information listed above it would seem sensible, yet this leads me to the next question.)

2. Assuming the starter is 1 liter, if the entire starter is pitched into a volume such as 5 gallons, would there be any negative effects from off-flavors that may have occured in the starter?

3. Considering the entire starter is pitched, and taking into account that yeasties "clean-up" after themselves would any of these off-flavors be reduced, or removed from the 5 gallon volume during and/or after fermentation?

4. Pitch at high krauesen, or chill and decant for a glycogen reserve?

Mr. Malty states he likes to pitch his yeast at high krauesen (usually 12-18 hours after preparing the starter) when the bulk of cell production is complete. I have been pitching at high krauesen, however, Mr. Malty doesn't focus on the factors discussed earlier, such as off-flavors caused by over-pitching, temperature, or affects on larger volumes.

I'm sure there is more than one school of thought on any number of these topics. My personal belief, without actually looking into the science, is off-flavors caused by a 1 liter starter would not affect a 5 gallon volume of wort. Again, this is my personal opinion, and I have been successful brewing and pitching entire starters (at high krauesen).

What are your thoughts?

 

[enderwig]

You need one more option, I do both depending on circumstances.
If I plan enough ahead, I chill and decant.
If not I pitch at high krausen.
Keep in mind I build up from slants so each "starter" is really 2 or 3 built up starters.

 

[ifishsum]

I've not heard much about off flavors specifically caused by overpitching so much as a lack of desirable ones. From what I understand you get a very clean fermentation - too clean in fact for many styles that depend on some yeast ester flavors. But not necessarily off flavors per se. Pitching on a cake for instance, is definitely overpitching - I've done that several times with a clean american ale yeast, and not ever experienced off flavors. I wouldn't do that with a hefeweizen though, because I like the banana esters produced by the hefe yeast.

As far as oxidation is concerned, I'm not worried about it because it takes a while to develop - far longer than I'll be storing a fermented starter. And any oxygen pitched into the wort will be consumed or scrubbed by the yeast during the growth and primary fermentation stages, so I guess I don't really see it affecting the final product.

Most of my starters are 1 quart or less and pitched at high krausen. Because of the dilution rate I'm just not worried about off flavors with that. I have made a couple of larger sized starters and decanted them.

 

[ajf]

I voted for pitching the whole starter, but the truth is that I do both.
For starters less that 1.5 liters (90% of them), I pitch the whole starter, and for larger starters, I just pitch the slurry.
I'm sure you can get off flavors from over-pitching if you pitch a vast excess of yeast, and let the beer ferment completely for a prolonged period of time on that excess, but a starter only exists in this state for a short time before pitching into the wort when the overpitching condition ceases to exist.
As for oxidation, there is a big defference between oxygenation and oxidation. Oxidation occurs quickly at high temperatures, or slowly at lower temperatures. In the case of a starter, the yeast is using all the oxygen it can get, and not leaving free oxygen long enough to cause oxidation.
I agree that starting at a higher than optimal temperature could cause some off flavors, but it also builds up a sufficient quantity of yeast to metabolize those off flavors. i.e. by the time fermentation is finished, those off flavors will be gone.
These are my thoughts, backed up by absolutely no scientific evidence, but it seems to work for me, so I must be right.
Seems like you're right as well, and ifishum seems to agree with both of us.

-a.

 

[Schnitzengiggle]

Thanks for the comments . Very good points, ajf and ifishsum especially about the oxygen being completely used up by the yeast in the starter as well as in the wort.

So I will say the consensus is: no real off-flavors, if any, are normally detectable in the finished product from pitching an entire yeast starter.

Thanks again, and everyone please continue to vote in the poll!

 

[bob1852]

that's why I use notty or US-05