A Series of Questions

I'm not a heavy poster here, but I read alot and understand the wealth of knowledge on these boards. I've been brewing for a few years and have a few questions that I've read about but am still unclear on...sorry for the number of questions. It's just a bunch of annoying stuff I still don't understand.

1) Wort Aeration...I understand that yeast needs oxygen to do its job effectively. I'm confused by the addition of oxygen to wort at different times. I know it can give off flavors, but aerating wort seems to come just before adding yeast, so I'm unsure when the exposure to oxygen is actually going to cause the off flavors.

2) Yeast Starters, Yeast Washing, Yeast Cakes...
a. First, with regard to yeast starters, I haven't been religious about making a starter, mostly because I don't have the equipment and only do it when I have access to my friends. With this said, I've never had much of a problem. My yeast (whether it be dry or liquid) has never had much of an issue getting going, so really what is the added benefit. I know you will get a more vigorous fermentation, and that can be helpful on higher gravity beers, but does it do anything other than ensure your yeast is healthy before pitching?

b. With regard to washing yeast. I've never done it but going to try on my next batch. I've seen the illustrative descriptions on how to do it. I'm a little unsure of some of the process in the cleaning process.

first, when you let the yeast settle then pour off the liquid on top, will the yeast be relatively solid on the bottom, or is there a trick to pouring off the top liquid portion?

Once you have poured off the top portions and you have a few mason jars of washed yeast, do you combine the jars to have 1 full jar or do you have a few quarter full jars laying around?

When reusing, how much do you pitch and does this necessitate a starter?

Finally, I know people use yeast multiple times, I've heard of people on their 8th generation of yeast...does this mean it has been washed and reused 8 times?

Does the yeast get stronger/weaker with each generation?

How do you avoid off flavors when using the same yeast but making a different beer?


c. Yeast Cakes...what exactly does the term 'yeast cake' refer to?

rootbrewskies said:

1) Wort Aeration...I understand that yeast needs oxygen to do its job effectively. I'm confused by the addition of oxygen to wort at different times. I know it can give off flavors, but aerating wort seems to come just before adding yeast, so I'm unsure when the exposure to oxygen is actually going to cause the off flavors.

Click to expand...

Generally you want to aerate after chilling the wort but before pitching yeast. Supposedly aeration while the wort is still hot can cause off flavors (known as HSA), and aerating the wort after fermentation is well under way can definitely cause a stale beer flavor. You want plenty of oxygen for the yeast to thrive, but you don't want it to remain in your beer after fermentation.

rootbrewskies said:

2) Yeast Starters, Yeast Washing, Yeast Cakes...
a. First, with regard to yeast starters, I haven't been religious about making a starter, mostly because I don't have the equipment and only do it when I have access to my friends. With this said, I've never had much of a problem. My yeast (whether it be dry or liquid) has never had much of an issue getting going, so really what is the added benefit. I know you will get a more vigorous fermentation, and that can be helpful on higher gravity beers, but does it do anything other than ensure your yeast is healthy before pitching?

Click to expand...

If you're just doing 5 gallon low-to-moderate gravity ales, starters probably are not really necessary. A lot of times I just pitch straight from the vial. But for high gravity ales and most lagers, a starter really can help ensure fermentation is efficient and produces less off flavors from stressed yeast.

At least that's my understanding....

1) Aeration is important for yeast in the very beginning. They need it to be able to multiply and also to build cell walls. Once the oxygen is gone, they can no longer multiply and the number of yeast cells you have at that time is the maximum number of cells you will have for the duration of fermentation. You want to give them the best chance to make your beer great, so plenty of oxygen is a great helping hand to offer them. Once they complete the aerobic phase of the fermentation cycle, they go into the anaerobic phase. This is where they make ethanol. Once this phase begins, you no longer want to introduce oxygen into the mix; they don't need it anymore and it will begin oxidizing your beer and producing off-flavors.

2 a) Yeast starters allow your yeast colony to go through an early reproduction phase to ensure they are healthy and have a sufficiently large number of soldiers ready to go into battle. The starter will reduce lag time, which reduces time for bacteria to begin munching on the wort. You want to give the yeasties their best chance at making great beer.

2 b) If you give the yeast enough time cold-crashing, it should be pretty well compacted on the bottom, allowing you to easily pour off most of the liquid on top. If you are following the guide that you were reading, you would leave them in separate jars and use each one of the jars in much the same way you would use a White Labs vial - grow a starter, pitch into wort, wait.
It is a good practice to use a starter - you'll be able to make sure the yeast survived (they probably did) and you will give them a chance to wake up and build a bigger colony before pitching.
Results on using yeast over multiple generations are subject to wide variability. Temperature, OG, water composition, etc can all put different stresses on the yeast. As you get further into the generations, mutations are more likely to develop. This could lead to off-flavors, or perhaps you will find a mutation that is the best yeast you have ever used. Hard to predict how something will mutate... 8 generations is a pretty good run, I think.
To avoid off flavors, clean your yeast using properly sanitized equipment and be sure to remove as much trub as possible. Keep it cold after harvesting. Make a healthy starter. And also make sure you use properly sanitized equipment. Did I mention the sanitizing thing yet? Good.

2 c) That is the layer on the bottom of your fermenter. If you use a secondary, that layer is almost entirely yeast. If you don't, then the layer is composed of trub (bottom portion of gunk) and yeast (upper portion of gunk).

When you wash the yeast,use a large clear jar or jug. Use boiled & cooled water to get the yeast & trub out of primary. Put it into the jar/jug to the threads. or near there. Let the darker trub settle,then as you see the lighter colored yeast dusting on top of the trub,pour that into sanitized jars with sanitized lids. That's the yeast you wanna save labeled in the fridge. you'll see it settle down quite a bit as it sits in there. I was thinking to make more boiled/cooled water so I can pour off the liquid,watery beer leavings & replace it with clear water to thin the beery aspect of it way down. That way it'll matter less what kind of beer I use it in next...

You can aerate anytime before fermentation has actively begun - even several hours after pitching (which you might do if you forgot or didn't have time prior to pitching or if you have a big beer and want to reaerate to add more oxygen). Once fermentation has actively started, you want to limit the amount of oxygen exposure since oxygen will chemically interact with ethanol and other fermentation products to produce other compounds that can give the beer off-flavors. Hot-side aeration has pretty much been debunked...or at least is no longer thought to be a major issue.

I found the Yeast Washing Illustrated to be a lot to take in until I did it.
I buy a fresh Pack of Wyeast 1056 and 1098 the first brew of my season in September. I wash and grow that yeast until the last batch I brew the following May. I don't brew in the summer due to temp control and time. My AG system often yields enough extra to get 3-4 quarts of ~1.040 wort. I boil that until it is sanitized, chill it to <70, put it in a gallon jug and pitch the harvested yeast. I let it run its course and refrigerate until the yeast is nice and tight. Until recently I was splitting my 10 gal batches so I would pour off the excess liquid, mix the rest up with the yeast and divvy it up into 3 pint jars. Pitch one of each in a carboy and save the 3rd to grow again.
This method allows me to spend ~$15 on yeast for about 150 gallons of beer.

Thanks for the answer guys. Really helped clear up some of the questions I felt I should have known the answer to but didn't.