The spoiled batch, which had been in the keg for about 2 weeks had the following properties:

• Initial flavor was anti-septic (almost burning).
• Murky appearance (different than chill haze).
• Slippery mouth feel.
• Finshed soapy, with the flavor getting more pronounce, to the point I spit it out. The bitter antiseptic flavor lingers on the tongue.

What the heck! Had I gotten a lax on sanitization? Was my yeast bad? Was there something in the brewing process that lead to this? I asked some home brewing experts and they attribute this to a yeast deficiency – either an infection, or bad yeast. It turns out there were two main factors, repitching of yeast and a dirty spigot in my fermentor. While I am not sure which did more damage, I have evidence of both.

Here is what the carboy looked like, note the ring:

If you have a goopy ring around the krausen layer you might be in trouble. The off gases from the fermentation also smelled ‘cheesy’, which tipped me off there might be a serious problem.

Beer Forensics:

For what turned out to be the spoiled batch, I opted to re-pitch yeast (Wyeast Northwest Ale 1332) from a previous batch of IPA. The harvested yeast was in the fridge in a ball jar for about 2 weeks. That IPA was already in the keg and was drinkable, but it was not my best batch ever. It had a thin finish and there were some light ‘chemical’ flavors present that come and go from sip to sip. I figured at the time, the beer was just green – and it did improve a lot after a month went by. When I kegged the IPA and harvested the yeast, it looked and smelled fine, a fresh bready aroma was present. That meant it is good to go right? WRONG!

Something funny happened with the fermentation of that IPA. One night I forgot to set the furance at 64F, and instead turned it all the way down to 58F – so it got pretty cold in the house that night. It turns out NW Ale 1332 does best between 65F and 75F. In effect, that night the yeast were really stressed. I didn’t think much of it at the time. I do recall the fermentation slowed after that. I also left the IPA in the primary for 23 days, without racking, and then harvested the 23 day old yeast cake. In retrospect I should have spent the $4-$7 for a new yeast pack. Even though that yeast cake smelled good at the time, it was no longer to be trusted given its age, and the temperature fluctuation.

I gathered two ball jars from the yeast cake. Now a month later, on inspecting the second ball jar, there is a thin line of black mold growing on top. YUCK!

That IPA was fermented in a plastic bucket with a spigot. The subsequent failed batch was fermented in a glass carboy. I went ahead and tore apart the spigot on the bottling bucket, and look what I found in there:

It had probably been over 3 years since I setup that bottling bucket and spiot. Whoops! No doubt whatever mildew / mold / germ was living in there is not good for the beer. I terminated it with extreme prejudice – a strong bleach solution!

After I soaked everything, I thought I was ready to go again, but then I noticed, inside the sealed part of the spigot, there were some faint black spots. It is hard to see in the picture, so I enhanced the second one.

The mold / mildew, whatever it is, is growing INSIDE the sealed part where the spigot rotates. There is no way to scrub that section. I am looking into getting a different type of spigot that does not have this design flaw.

Yeast Re-pitching Revisited:

All this time I had thought I was being a good sport by re-pitching yeast. That is what the pro’s do right? Well, it turns out I did not realize the risks associated. I wrote an article awhile ago that praises yeast washing, and another on yeast repitching. I have updated those articles to point out what was learned here. The time it takes to harvest and clean the yeast (15-20 minutes), plus the risk is not worth the $3 savings it offers! I should have known that…

Key Take Aways:

• Yeast re-pitching can be risky and might not be worth the cost savings for home brewers.
• If you are going to repitch – I would rack after about a week and save that yeast. Let the secondary fermentation finish on its own, and discard that smaller, older yeast cake. I would also be very strict about temperatures ranges and sanitization. I successfully repitched many many times, but now I am starting to see where perhaps some inconsistency came into play.
• Tear everything apart now and then and completely clean it with PBW or a bleach solution if the materials are compatible with bleach.
• Look for stuff growing inside what appear to be sealed parts, such as the spigot on the bottling bucket.

PROST!

Originally, I didn’t get the name. Were they being cute? Does it ‘pack’ a punch? No, I was not thinking literally enough. While on vacation it dawned on me. The name was inspired from the old arcade game! It helped that weeks before my vacation I had played the Pacman game on Google (http://www.google.com/pacman/). What Pacman does in the game, and what brewer’s yeast does in the wort are pretty similar.

To help us all remember, I created a somewhat crude and juvenile drawing. This makes for a basic lesson in ‘God Is Good’, aka yeast, and how they turn sugar into alcohol:

Our big hungry yellow hero ‘Pacman’ is a yeast cell (technically a fungus). Him, and thousands of his brothers and sisters eat their way through sugar molecules in sweet wort. As they consume the sugar they produce alcohol, carbon dioxide, and some sulfur dioxide. Yes, alcohol is fungus crap. Poetic. The SO2 is why if you take a sniff from the airlock it can smell a little funny. This varies by yeast strain. Normally I smell hop aroma from my airlock, but I have smelled ripe odors from Hefe and Kolsch strains in particular.

There are some oversimplifications here. Yeast need oxygen to do well. That’s why it is important to aerate! Yeast also utilize minerals and other compounds present in the wort. As the yeast eat, they reproduce faster than rabbits. Healthy fermentation is like a wild orgy on a microscopic level.

When the party is over there will still be some sugars remaining. Some brews, like dry mead, use a yeast strain that goes all the way to a final gravity near 1.000 (no sugar left). Each yeast strain has a different alcohol tolerance and capacity for digesting complex sugars. The yeast eat themselves into an environment they cannot survive in. That’s okay though, they can be harvested off the bottom and saved for another batch or immediately repitched if all was well with the fermentation.

SANITATION: You must sanitize everything in this process! Storing yeast successfully is fully dependent on keeping the samples pure.

YEAST STOCK: You will harvest the yeast that you are about to wash and store from a recently (same day) emptied fermenter. This yeast cake or slurry will be the basis for all that you are about to do. This is the yeast that will go on to propagate new colonies in future brews. See Fig 1

Fig 1.

HARVESTING: After racking the fermented beer from atop a yeast cake, there will generally be some liquid left along with the yeast cake. Swirl this around and loosen the yeast cake so that you can pour the slurry (sometimes chunks) of yeast into a sanitized flask or 1 gal. carboy. You want plenty of spare volume. Your yeast slurry will be full of trub, some break material, and hop particles. Currently, it is probably looking VERY thick and has no defined layers, though we are about to fix this! Fig 2

Fig 2.

WASH: You will want to have about a half gallon (ample amounts) of boiled and cooled water on hand (so we don’t cook the yeast). In your flask or carboy use enough of this water to double or triple the volume of the slurry that you currently have. Give it a few swirls to mix all of the contents (slurry and water) together. Cover with sanitized foil. See Fig 3

Fig 3.

WAIT: Given as little as 15-20 minutes to sit, you will be able to see some drastic stratification in your slurry. The heavier particles, trub, and break material will settle out quite quickly, leaving a dark layer with progressively lighter layers above it. Atop these dark layers you will have a creamy layer of liquid. This is what you want, water and yeast in suspension. See Fig 4

Fig 4.

SEPARATION: You will want to have several sanitized jars available to decant this creamy, yeast filled liquid into. Pour the creamy liquid containing the suspended yeast off of the sediment and into as many jars as it takes to hold it. Now you will have 2-4 jars full of this creamy looking liquid that you will place sanitized lids on, and then place into the refrigerator. See Fig 5. After some time has passed in the fridge you will see that the liquid is now much clearer and there is a nice bright layer of clean yeast at the bottom of each jar. See  Fig 6

Fig 5.

Fig 6.

STORING: If your sanitation practices are good, you can store this yeast for months. The yeast should remain in these jars, sealed and refrigerated, until you are ready to make a yeast starter to awaken them. It would also be a good idea to mark these jars with the yeast name, the date, and R1, for “reuse #1″, This way you can keep track of how many times you have re-used this yeast. See Fig 7. Typically after repeated uses the yeast will begin to mutate and its characteristics may change to a degree. You can typically feel confident re-using yeast 4-5 times before degradation is detected.

Fig 7.

RE-USING: When you would like to re-use this strain of yeast, simply allow a single jar of washed yeast to gradually warm to room temperature, decant the liquid and pitch the washed slurry from the bottom of the jar into some new starter wort. See how to make a yeast starter HERE.

IMPORTANT NOTES:

1. You can NEVER be too careful with sanitation when it comes to yeast washing/storing.
2. Do use a large clear glass container (large flask or 1 gal. carboy) for the HARVESTING and WASH steps in the process.
3. Ball or Mason jars make excellent containers for the WAIT and STORAGE steps in the process.
4. Be sure to sanitize the jar lids before securing them and storing your yeast.
5. Mark your jars with the yeast name, the date and the reuse/generation number (R1, R2,…) and so on to keep track of how many times you have washed this yeast and re-used it.

Update 11/12/2011: Check out the article on Bad Batches to see why you might want to avoid re-pitching yeast, or if you do so, make sure to understand the risks involved.

The stir starter comes complete with everything you need. It measures 4”x6” which is fine for up to a 1 gallon vessel. Any Erlenmeyer flask for yeast starters would fit comfortably on StirStarter.

It includes a rubber mat for the top so the flask grips the surface nicely.

Stir bar, catch magnet, instructions, and power supply (not pictured) are also included.

Using the StirStarter is simple. A yeast starter is prepared as normal. A sanitized magnetic stir bar is dropped into the flask containing the yeast starter. The stir bar is then centered in the bottom of the flask with a catch magnet (kept on hand). The flask is then set down on top of the stir plate. Gently the spin speed is increased to a steady rate. A whirlpool effect is not needed. If the dial is set too high the magnet can get spun off center. The spinning stir bar continuously mixes the contents of the flask. This increases the surface area potential of the yeast, leading to more yeast activity.

Some other notes about Dan at StirStarter. He ships fast, my package got here within three days. There is also a lifetime guarantee on the product. That is hard to beat.

In case you are thinking about building one yourself, here is the inside of the unit:

There are a few things going on in there involving electronics that have to be correct. One is the power level for the fan, the other is the wiring for the speed switch. The StirStarter website provides instructions on how to build your own. After just a couple seconds of reading, I realized building my own would be trouble. It would take me several trips to the electronics store and the better part of a weekend to build my own.  At the low price of the StirStarter, there is not much savings potential over buying a StirStarter worry fee built by a pro.

This site will feature an upcoming article about yeast washing, which explains saving and recycling yeast over and over again.

* According to MB Raines’ article about yeast starters, stirred yeast starters can get as much as ten times the amount of active yeast compared to a standard shaken yeast starter. According to the brewersfriend.com article on stir plates, it may be closer to a 50% increase.

StirStarter was kind enough to hook me up with a StirStarter for writing this post.

• Starter recommended?: YES and NO **see commentary below.
• Starter size (for 5 gallons): 3L
• Starter OG: 1.040 – 1.050
• Starter incubation time: 24-48 hours
• Blow off recommended?: NO
• Optimum fermentation temperature: 48F-59F
• Suggested ambient air temp during first 24 hours of fermentation: 53F
• Suggested ambient air temperature after 24 hours of fermentation: 53F
• Scent during fermentation: Sulfur
• Flavor profile: Very malty and clean, great for German lagers and pilsners, low diacetyl
• Flocculation: Medium
• Attenuation: 73%-77%

**Being that W-34/70 is a dry lager yeast, a yeast starter is not necessary under one condition… you pitch enough of the re hydrated dry yeast to properly inoculate the wort.  www.MrMalty.com contains a yeast pitching calculator which will guide you as to how much dry yeast you will have to pitch in your lager.

**A lager with an OG of approximately 1.050 will require (2) 11g dry yeast packets, OR a 3 liter starter. In this case I would prefer to pitch (2) packets of re hydrated yeast and forgo the starter, here is why. The dried yeast is ready to ferment, it is packed with nutrients, and while using (2) packets you will meet or slightly exceed the required yeast count for your wort. Even a 3 liter yeast starter, though still meeting the required yeast count for your wort, will have burned up much of the stored nutrient reserves that were in the dry yeast prior to creating the starter.

Pitching the re hydrated dry yeast will give you a faster start for this reason. Two packets of W-34/70 will cost you about $6.00, . If you prefer to create a starter while using W-34/70, see how to make a yeast starter at brewersfriend.com.

When pitching lager yeasts, there are two methods by which to do it, pitching warm or pitching cold. A warm pitch will take place at a temperature of 65-70F, then the temperature is slowly lowered to the ideal fermentation temperature of 48-59F. This is done by some brewers to accelerate the start of the fermentation and lessen the lag time, it will also require a slightly lower pitching rate for these reasons.  There are concerns however of off flavors being produced from the limited time at warm temperatures, but the yeast can clean this up with a diacetyl rest after primary fermentation.

Pitching cold is simply the process of pitching yeast at fermentation temperatures ranging from 48-59F. This will result in a slightly longer lag time and require a healthier yeast count to get fermentation started in a timely manner. This is preferred however by many lager brewers to avoid any possibility of off flavors that can be created during a warm pitch.

Considering the high quality of this yeast strain, the ease of use as a dry yeast and its popularity in brewing circles around the world, it is a must try both for the novice and advanced lager brewer. Buy (2) packets, rehydrate them and pitch straight into your wort.

The beer turned out very clean, slightly malty, it was a great example of a German Pils. I am enjoying it thoroughly after about 2 months of lagering. Enjoy!

A stir plate is a simple machine consisting of a base which houses a motor with variable speed control. Fig 1. This motor is used to spin two precisely spaced magnets, which in turn will spin a magnetic stir bar inside your flask. The intent here is to use this stirring motion to:

1. Keep the yeast in suspension
2. Release CO2 from the starter solution
3. Continuously aerate the starter liquid

Fig 1.

There are several important guidelines to follow when utilizing a stir plate to create a starter:

1. Ideally, boil the starter wort in the flask that you will be using to create the starter, this will help to sanitize the flask.
2. DO NOT use an airlock on a stir plate starter as it will impede the ability of the stir plate to exchange CO2 from the fermentation for O2, which will help grow yeast.
3. DO use foil to cover the top of the flask instead of an airlock.
4. Ferment the starter at 75F – 80F. While not optimal for flavor production, you are trying to grow yeast, and warmer temperatures will accelerate this process.

By doing the above, you are creating the perfect growing environment for your yeast cells, allowing them to grow at a much greater rate than they would with the use of a simple starter with no stir plate. After the starter has fermented out completely (approx 24 hours), remove the starter from the stir plate and chill so that the yeast may settle. After a short period of time (several hours), the yeast will form a nice thick slurry in the bottom of the flask, allowing you decant the starter wort prior to pitching. Decanting is required since the wort has been oxidized and fermented at a higher temperature than is optimal for most yeasts (75F-80F recommended). Though this temperature is excellent for yeast growth, it does not leave a very favorable flavor in the starter liquid.

There are calculators that will help you to determine the size of starter needed, and/or the volume of yeast slurry needed to pitch the optimal number of yeast cells into your wort. One such calculator can be found at www.MrMalty.com. This calculator will allow you to enter all of the vital statistics about your wort so that it can properly calculate the number of yeast cells you will require, the required volume of your starter wort and the volume of yeast slurry that you must pitch to meet your ideal pitching rate.

Below is a side by side comparison of the number of yeast cells created in a 2L simple starter (no stir plate) and a 2L stir plate starter. The results may surprise you!

Starter volume: 2L
Amount of Yeast used in starter: (1) 11g packet
Fermentation Time: 24 hours
Temperature: 75F (recommended to quickly grow yeast)

Using the above criteria, a simple starter will produce approximately:

201 billion yeast cells
82 ml of yeast slurry

Using the above criteria, a stir plate starter will produce approximately:

307 billion yeast cells
124 ml of yeast slurry

As you can see from the above comparison, utilizing a stir plate you are able to increase by 50% the yeast count with the same amount of starter wort while using the same amount of yeast pitched into said starter. Conversely, you can also create the same amount of yeast in a stir plate starter as you are able to with a simple starter, with nearly half the starter volume. The latter is of great interest to lager brewers who will routinely need to create very large starters to reach the proper pitching rate for their lager beers. Lagers will routinely require a 3L-4L stir plate starter. If you utilized a simple starter (no stir plate), you would be in the neighborhood of 6L to reach the proper pitching rate.

One yeast that I can give nothing but rave reviews to is the WLP300 German Hefeweizen yeast. From the quick start, the raging fermentation and excellent final flavor profile, this yeast is a show stopper in your summer Hefeweizen. Below are some stats on this yeast and how I have effectively used it in my beers. Mrmalty lists this as the strain as Wyeast 3068 Weihenstephan Weizen Yeast.

• Starter recommended?: YES
• Starter size (for 5 gallons): 1 quart
• Starter OG: 1.040 – 1.050
• Starter incubation time: 24 hours
• Blow off recommended?: YES
• Optimum fermentation temperature: 68F-72F
• Suggested ambient air temp during first 24 hours of fermentation: 65F
• Suggested ambient air temperature after 24 hours of fermentation: 70F
• Scent during fermentation: Bananas
• Flavor profile: Bananas and cloves
• Flocculation: LOW
• Attenuation: 72%-76%

Liquid yeasts yield a much lower cell count than the common 11g dry yeast packets. Dry yeast are also packed with nutrients and reserves so they are ready to ferment immediately after being re hydrated, liquid yeasts are not. This is why a starter is imperative. 24 hours is all that is really required to get this yeast really cranking and ready to pitch. See how to make a yeast starter at brewersfriend.com.

Typically with this yeast, my beer OG is low, 1.040 – 1.050 and the volume is 5.0 gallons. For the proper pitching rate for the above described conditions you will need about 158 BILLION yeast cells, requiring a 1qt starter. Quickly boiling up some DME OR using your actual wort from your brew and allowing the yeast to incubate for about 24 hours is all that you need to get this yeast ready to brew.

The ambient air temperature is important to note with this yeast as it ferments. Optimum fermentation temperatures are tight, between 68-72F, so temperature control is imperative for good consistent results. After pitching, this yeast will require approximately 8-10 hours to show real visible signs of fermentation. Fermentation is violent, heating up the wort to at least 5-7F greater than the ambient temperature. Therefore when fermentation begins, it is best to keep the ambient temperature at approximately 65F for the first 24 hours of violent fermentation, after this point you should safely be able to raise the ambient temperature to 70F to finish the remainder of the fermentation. Due to the violent fermentation associated with WLP300, a blow off tube is required, you can expect up to a quart of fluid to blow out of a typical 6 gallon fermenter.

Please note that on each vial of White Labs yeast it claims to be pitchable yeast, direct from the vial. While this may be true, in most cases you will be under pitching into your wort, experience a longer lag time and a less desirable fermentation.

See how to brew the CCB Hugh Hefeweizen with this yeast at brewersfriend.com.

When to use a yeast starter:

• When brewing a beer with an OG of 1.080 or greater.

• When brewing  a Lager beer – the colder fermentation temperature requires a higher yeast pitching rate.  A 1-2 quart starter has always been sufficient for my five gallon batches of Munich Helles or Oktoberfest.
• If your yeast is old or past its expiration, stepping it up with a starter is a safe bet.
  

What you need to create a simple starter:

• Extra light DME (3-4oz)

• 1 quart water

• 4-6 quart sauce pan with lid

• Pyrex flask or a 1 gallon glass carboy

• Tin foil

• Room temperature liquid yeast or dry yeast that has been re hydrated in 95F-105F water

The process:

• Bring 1 quart of water to a boil in the sauce pan.

• Measure 3-4 oz of DME and introduce this to the boiling water, stir well, boil 10 minutes.

• Remove from heat, placing lid on the sauce pan.

• Cool the starter wort in a shallow, cold water bath or in the refrigerator until it reaches the target fermentation temperature of the beer you will brew with it.

• Once cool, pour the starter wort into a sanitized flask or carboy.
  

• Secure a piece of tin foil on the opening of the flask or carboy and shake vigorously to aerate the wort.
  

• Pitch the yeast (add yeast into the flask / carboy containing the aerated wort).

• Seal container with a clean piece of foil, or a cork fitted with an air lock.

• Place starter in a dark area where it can maintain the proper temperature for fermentation.

When you are ready to use the starter you can swirl the flask/carboy to rouse the yeast and pitch the entire volume of the starter into your awaiting wort. Likewise, you can chill the starter after fermentation to facilitate the settling of the yeast, on brew day decant the “beer” from the flask/carboy and pitch only the yeast slurry left in the bottom. The starter should start bubbling in about 24 hours and can be pithced into your batch 24-48 hours later (ideal), or up to a week if you refridgerate it.

The strength of this “clumping” is determined by a host of factors from O2 levels in the beer, temperature, and nutrient levels, but the primary factor seems to be the strain of yeast itself (in truth, flocculation is still being researched, and has a few mysteries remaining.) Flocculation occurs near the end of the yeast life cycle, so a yeast that flocculates early will not convert as much sugar, and result in a lower-than-expected alcohol content. Strong flocculation gives a clearer beer, while weaker flocculation can lead to a cloudy beer, sometimes with a yeasty taste. Hefeweizen yeast is a good example of a strain that has very low flocculation, meaning a lot of it is left behind in suspension. Traditional non filtered hefeweizens should look cloudy from the yeast (not the wheat as some might think).  The clove like signature flavor in a hefeweizen comes from the yeast.

Attenuation describes the overall efficiency of a yeast strain in converting sugars into alcohol under a specific set of conditions. Higher gravity beers require the use of yeasts with higher attenuation rates. Attenuation is listed as a percentage, meaning the percentage of sugars present in the wort that get converted into alcohol. Most beer yeasts have a 65-80% attenuation rate. Wine & mead yeasts have a higher attenuation rate. The exact attenuation rate can be found for a given beer by comparing the starting (pre-yeast) original gravity (OG) to the final gravity (FG) of the finished beer.

When selecting yeasts, the beer style should be considered. When brewing a Belgian Witbier, a yeast strain with a 65-70% attenuation rate would be appropriate. A “stronger” yeast (higher attenuation) could be used, resulting in a higher alcohol content, but the overall flavor & style of the beer would be “off” from the standard. The attenuation for yeast for an English ale would be lower than the yeast for a Belgian brown.

The attenuation of a particular batch is affected by anything that would affect the health of the yeast. Unexpected flocculation, changes in temperature and insufficient nutrients can all lower attenuation.

Yeasts are living organisms. The distinction between ale yeasts and lager yeasts is based on the temperature range at which they are most active, and where in the wort-suspension the yeast concentrates. Ale yeasts are top-fermenting. During the most active stages of fermentation, usually within the first 5 days of pitching (or adding) the yeast to the wort, ale yeast is visible on the surface of the beer, amidst the foam and bubbles. Lager yeast is active at the bottom of the beer, and is easily missed after the first week as it mixes in with the sediment.

The top- versus bottom-fermentation is an aesthetic difference though; the real distinction is the temperature at which the beer should ferment. Ale yeasts ferment best between 60 -75 degrees F; (12-24C) going below this range slows fermentation, causing the yeast to be “sluggish”, while going above the range increases the risk of bacterial growth and other contamination, as well as causing off-flavors from the yeast. A friend’s batch of hefeweizen suffered because the home thermostat was set to cycle to lower temperatures at night.

Lager yeasts are a slightly different animal. While they ferment best between 35 & 55 degrees F (2-13C), for the first day, the temperature should be in the ‘ale’ range. This is because of the life cycle of yeast: for the first 12-24 hours, the yeast is converting starches in preparation of reproduction and releasing CO2. After this initial “blow off” is done, the beer should be placed in a temperature controlled environment (like a refrigerator) and gradually chilled down to lagering temperatures. Note ‘gradually’; when cooling the wort, the goal is to chill quickly to limit exposure to wild yeasts and bacteria. When chilling the beer to lager it, no dramatic steps are necessary, as the beer should already be in a carboy with an airlock. Sudden, rapid changes in temperature can ‘shock’, or even kill, yeast. Smaller batches are inherently more susceptible to temperature shock due to the smaller volume of liquid.

Some people prefer to make a lager yeast starter at room temperature, then pitch into cooled wort from the kettle, then move the fermenter into the fridge. Lager yeast may also need a dialectal rest, which involves raising the temperature into the 60-65F range for a couple days to let the yeast clean it self up. Diacetyl is a butterscotch like flavor and can be seen as a defect in certain types of lagers, especially light lagers.