Aeration of Starter,...NOT Wort,...Jamil ?

[jamilz]

You will find that the yeast changes quite rapidly if you keep reharvesting and repitching the least flocculent, most attenuative yeast (the secondary). It is strain dependent, but some lager yeasts will change in just two or three batches. I prefer to collect the entire yeast cake, rinse out the trub (and dead cells) and then pitch just the appropriate amount of yeast for the new batch. Not the entire amount.

As far as starters go, don't add hops. There are compounds in the hops that will stick to the yeast cells and really don't help the health of the yeast. If you're adding hops because you're worried about bacteria in your starter, then maybe you shouldn't be making starters.

The SG of the starter wort is a balancing act. The lower the SG, the easier it is on the yeast. However, there comes a point where you don't really get enough growth to make it worthwhile. If you're starting out with a trashed yeast (like from a bottle conditioned beer from Belgium) you should start at 1.020 (5 Plato). However, if you're interested in building up a vial of White Labs or an XL pack of Wyeast, you should target 1.040 (10 Plato). It just isn't worth the trouble otherwise as you'll get very little growth.

There is one thing I know for certain, and that is that there is plenty of "grey area" when it comes to working with yeast. There are so many variables, that it is pretty much impossible to say, "it always works this way for every brewer." We need to be open to the proof of great beer. I've met plenty of brewers flaunting the "rules" and making fantastic beer.

The more I learn about yeast, the more I realize I need to still learn about yeast.

[jamilz]

Just in case some folks don't know this, flocculation is the clumping together of yeast. Not the yeast dropping to the bottom. The more flocculent yeasts, like White Labs WLP002 will floc easily and they rise to the top with the CO2. Thus it is a top cropping or top fermenting yeast. A less flocculent strain, like most lager yeasts, clumps less and does not rise to the surface as much, thus it is called a bottom fermenting yeast. Once CO2 production has ceased, the larger clumps of yeast do drop to the bottom easier, but that is not flocculation.

There are a huge number of factors that will affect flocculation. Everything from very high propagation temperature to a lack of calcium to selective forces.

[madmacaw]

Jamil;

Thanks for explaining flocculation, I did not do so and I can see how some might confuse that with settling out of which flocculation just assists in the process due to increased weight.

As far as the SG of starter solution, if you are doing daily infusion of fresh wort, 5 deg. plato will always work well... this is also how yeast labs propagate (sort of... they actually continuously meter in the fresh wort). The premise behind this practice that I was taught at Siebel/Weihenstephan is that you should only supply enough sugar for reproduction needs, anything more could allow fermentation to begin.

As far as doing starters without daily infusions of wort, there may be some merit to making the starter at a higher gravity, but I have no empirical evidence to cite. I have never made starters that way and have no professional literature that spells out the best practices so I'll have to leave that up to others that have experience with that method.

How would the presence of hops in the starter solution harm a yeast propagation? That is one I've never heard before. Could you enlighten me further? And, yes, the hops are simply another hedge agains infection. (but I really don't think it means I shouldn't be making starters ) That is done really with the first infusion in mind where there is a bit of a lag before the pH begins to drop. In subsequent infusions, it would not matter. But, if you are making your starter solution in advance, you don't know which one is for the first infusion and which ones come later, so I do so anyway as I was unaware that it could be potentially detrimental. Based on your citations, I may change this practice.

To further expound upon the "bottom fermenting" vs. "top fermenting", the appearance that this is how they are fermenting (they actually are fermenting throughout the wort, so it is a bit of a misnomer) is mostly caused by the temperature of the fermentation. In a cool fermentation there is less convection combined with slower CO2 release since the metabolic rate of yeast are slower at this temperature. Hence the appearace difference between that of an ale fermentation. If you want proof of this, ferment at ale temperature with a lager yeast... it will appear very similar to that of an ale yeast fermentation at the same temperature.

Thanks!

[jamilz]

Jamil;
As far as the SG of starter solution, if you are doing daily infusion of fresh wort, 5 deg. plato will always work well... this is also how yeast labs propagate (sort of... they actually continuously meter in the fresh wort). The premise behind this practice that I was taught at Siebel/Weihenstephan is that you should only supply enough sugar for reproduction needs, anything more could allow fermentation to begin.

With continuous aeration and the gravity we're talking about, I don't think you need to worry about fermentation. Take a look at ASBC-1221-04R for an interesting experiment on propagation gravities and the impact on viability and cell size.

How would the presence of hops in the starter solution harm a yeast propagation? That is one I've never heard before. Could you enlighten me further? And, yes, the hops are simply another hedge agains infection. (but I really don't think it means I shouldn't be making starters ) That is done really with the first infusion in mind where there is a bit of a lag before the pH begins to drop. In subsequent infusions, it would not matter. But, if you are making your starter solution in advance, you don't know which one is for the first infusion and which ones come later, so I do so anyway as I was unaware that it could be potentially detrimental. Based on your citations, I may change this practice.

ASBCJ-63-0028 and another paper that I can't seem to find. While this first paper deals with the delta in viability between higher and lower IBU levels, the point is that the addition of hops does have an impact on the viability of yeast. It is probably minor at say 7 IBU, but so is the anti-microbial value of 7 IBU. You're far better off adjusting the pH of the starter than adding hops for protection.

To further expound upon the "bottom fermenting" vs. "top fermenting", the appearance that this is how they are fermenting (they actually are fermenting throughout the wort, so it is a bit of a misnomer) is mostly caused by the temperature of the fermentation. In a cool fermentation there is less convection combined with slower CO2 release since the metabolic rate of yeast are slower at this temperature. Hence the appearace difference between that of an ale fermentation. If you want proof of this, ferment at ale temperature with a lager yeast... it will appear very similar to that of an ale yeast fermentation at the same temperature.

I agree to some extent, but the difference is not just temperature. Most lager yeasts are FAR less flocculent than say White Labs English Ale Yeast, WLP002. At the same temperature, the WLP002 is going to make a much bigger layer of krauesen, because it is so much more flocculent, forms bigger flocs, and traps more CO2.

On a side note, would it be possible for you to use a bit less BOLD in your posts? It gets hard to read.

[madmacaw]

Thanks for the citations, I will dig through my ASBC binder and see what I can gleen.

You are correct, I could simply adjust the pH of the starter solution. I never had a reason to do so before given the evidently faulty information I was taught! Wouldn't be the first time.... I was twice taught (at both schools) a number of unnecessary (and detrimental) mashing techniques.

I'm sorry if I was not clear enough in my last post regarding the causes of the appearance differences in cool and warm fermentations. I thought the inclusion of "mostly" before temperature was enough. I never meant to imply that this was the only cause.

Sorry about the emboldened text... it is a habit that I got into on another forum after a postor remarked that it was hard to tell what were my replies vs. the quotations for which I was supplying answers, I'll stop.

[Push Eject]

This thread rocks.

Push Eject

[J.Brew]

So help me out here...I'm a little slow on the uptake..I should be aerating my starter using a stirplate or air pump to ensure healthy yeast growth and reproduction. If I am going to use pure oxygen in this situation I should do so before i pitch my yeast. When dealing with the wort I should aerate using an airstone for several minutes or hit with a minute or two of pure O2 before i pitch my yeast. After I pitch I should not be adding any additional oxygen in any form.....Sound about right??

[jamilz]

The way that works for me is to provide continuous aeration for the starter via either filtered air and/or a stir plate. This is pretty much error free, since you can't add too much O2 this way.

If you use pure O2, you need to be a bit more careful on your starter, you can hit it a few times with O2, but I wouldn't make it continuous. You're going to have to experiment to find a rate that works best for your yeast and your style of brewing.

For the batch of beer itself, repitching yeast, I prefer to oxygenate the wort shortly after pitching the yeast. I use pure O2 in this case. 1 liter per minute for 1 or 2 minutes works well for me.

If you're not going to add O2 to the wort, you're going to need to pitch more yeast than if you do add O2. For me, I tried a number of batches of lagers (Ofest) with no O2 and more yeast to limit growth in the beer. A lot of people told me it wouldn't work, but the resulting beer was quite clean. Very clean. Too clean. The beer ended up seeming a little dull overall. I switched back to targeting some yeast growth in the beer. As the folks from Wyeast and White Labs will tell you, you must have some yeast growth or the beer just doesn't taste right.

I think Eric's point (please correct me if I'm misstating your point here) is that you're better off getting the yeast all the O2 they need prior to pitching and then adding them to the beer, versus adding sterol deficient yeast to the beer and then adding O2 for them to uptake.

The interesting thing here is that most yeast you're repitching is probably not in the best shape and you need to get it some O2 if you want it to grow again in the next batch. Most folks add it to the wort and then add O2. If you're making a starter, then you can juice them up before they go in the wort.

In any case, the important thing is to manage the amount of yeast growth, the pace of yeast growth and the health of the yeast. I think it is far more important to pitch healthy yeast than it is to pitch the right quantity of yeast. Both are really important, but that is how I rank them.

I agree, it is really cool that Eric has joined the forum and is helping illuminate a very complex subject.