Too Much Yeast? Finishing strong, tricks to a hefe, and priming sugar uses

Q
It seems like I often hear about the “dire” effects from under-pitching yeast, but can’t say I’ve heard much about the consequences of over-pitching, besides the advice of: “Don’t do it.” Would love to hear what problems are associated with over-pitching yeast, notably over-pitching with yeast slurry? 
Jon K. Rodrigo
Manila, Arkansas

A
Averbelen et al. (Impact of Pitching Rate on Yeast Fermentation Performance and Beer Flavour, Applied Microbiology Biotechnology (2009) 82:155–167) demonstrated that increasing pitching rates of lager yeast from 10 to 120 million cells/mL resulted in an increase in fermentation rate, decreased net biomass production when pitching exceeded 80 million cells/mL, higher post-fermentation levels of diacetyl, and minimal changes in overall beer flavor and yeast viability after fermentation. This group suggested that reduced cell production with higher pitching rates may present viability and vitality problems in subsequent fermentations because of a higher percentage of older cells in these yeast crops. A key takeaway from this study is that fermenter residency time for lager beers can be reduced by increasing pitching rate above 10 million cells/mL with minimal flavor differences in the finished beer.

Performance and Beer Flavour, Applied Microbiology Biotechnology (2009) 82:155–167) demonstrated that increasing pitching rates of lager yeast from 10 to 120 million cells/mL resulted in an increase in fermentation rate, decreased net biomass production when pitching exceeded 80 million cells/mL, higher post-fermentation levels of diacetyl, and minimal changes in overall beer flavor and yeast viability after fermentation. This group suggested that reduced cell production with higher pitching rates may present viability and vitality problems in subsequent fermentations because of a higher percentage of older cells in these yeast crops. A key takeaway from this study is that fermenter residency time for lager beers can be reduced by increasing pitching rate above 10 million cells/mL with minimal flavor differences in the finished beer.

Empirical observations with pitching rates less than 10 million cells/mL suggest that ester and higher alcohol levels increase as pitching rates decrease and total cell growth increases. Restricting pitching rates when brewing certain beer styles, such as hefeweizen, is one method used to increase fermentation-related aroma compounds. One downside of increasing yeast density for certain styles of beers may be reduced ester production.

In practice, high pitching rates can be difficult to achieve when growing liquid yeast for first generation use because high pitching rates require a relatively high percentage of yeast pitch. Many brewers, especially homebrewers, grow yeast in wort that is different from the beer being brewed. And most brewers pitch the entire slurry of propagated yeast. This means that higher pitching rates will likely dilute the wort brewed for a particular beer with propagation wort. This dilemma is easily addressed by homebrewers and smaller commercial breweries by using dry yeast.

Dried yeast use is not as common in larger commercial breweries because of the cost of dried yeast in comparison to yeast produced in propagation system. There are also general concerns about re-pitching yeast crops from fermentations started from dried yeast, making liquid starts the most common in larger commercial operations. These brewers can concentrate cell density by allowing propagated yeast to sediment or they can increase cell density using a centrifuge. I am not aware that either of these methods is commonly used by commercial breweries to concentrate cell density following propagation. However, pitching high-density yeast slurry harvested from a fermenter is common and allows brewers to increase pitching rates without excessive wort dilution (harvested slurry typically contains approximately 1 billion cells/mL compared to slurry from a propagation system with approximately 100-150 million cells/mL).

Aside from better equipment utilization, another practical benefit to increasing yeast pitching rates is faster net uptake of wort nutrients by yeast, faster pH reduction, and a faster increase in ethanol concentration. All of these changes reduce the chances of beer spoilage related to wild yeast and bacteria.

In answer to your basic question, there are no major, stop-the-press, problems associated with increasing yeast pitching rates. Most practical brewers are conservative when it comes to changing brewing methods. If you want to experiment with upping your pitching rate, consider moderate increases over time to determine how these changes affect finished beer quality and harvested yeast health. In my book, slow and steady wins the race!

Q
I have a fermentation issue with a New England IPA I just brewed. It’s been in the fermenter at ~65 °F (18 °C) for 22 days and it is taking longer to finish fermenting than usual. By now it should have been finishing fermentation below 1.020, but I have two fermenters over 1.020 (1.022 and 1.024); the other one is 1.018 (I brew 50-L/13 gal. batches and split them into (3) 5-gallon (19-L) fermenters).

This time I made a 3-L (3-qt.) starter with one vial of White Labs WLP008 (East Coast Ale). Two days ago, I used another WLP008 vial and added a third of the vial in each fermenter. I see activity from the airlock but it is taking a lot of time. My inquiry here is what I should do next? Should I add another WLP008 vial? The final gravity should be around 1.012–1.015.

I have two different hydrometers, so I trust the measurements. I mashed a blend of pale malt, malted oats, white wheat malt, and Vienna malt at 151 °F (66 °C) for an hour. the starting gravity was 1.061.
Roberto Caballero
Lima, Perú

A
Whenever there seems to be an attenuation problem with a batch, I think it always helps to go through a mental check list of the basics. This checklist of mine includes the following:

• Mashing issues?
• Yeast nutrients and/or zinc added to the wort?
• Yeast into wort cooled to the correct temperature?
• Wort aerated normally?
• Sufficient yeast added to the fermenter?
• Anything unusual that may have caused an early end to fermentation?
• Yeast strain known for lagging fermentation?
• Final gravity known?

I am going to run this list to illustrate a point about mental checklists, so bear with me while I talk to myself!

Mash OK? It looks normal. 151 °F (66 °C) for an hour puts the mash right in the middle of the peaks for beta and alpha amylase. All malts had good enzyme levels (nothing really high kilned) and the adjunct ratio looks OK.

Nutrients added? Hmm, I typically don’t worry too much about FAN (free amino nitrogen) or phosphorous with all-malt worts, so did not add nutrients to this batch. Should consider this topic more for the next brew. I did add zinc to the wort (0.20 mg/liter). I am not thinking that nutrients are the issue.

Wort temperature OK? Wort was cooled to 61 °F (16 °C), pitched with yeast from my propagation at 65 °F (18 °C), and the fermentation was allowed to free-rise up to whatever temperature was in the fermenters with a room temperature of 65 °F (18 °C). Not sure what the actual fermenter temperature was, but probably not too cool or too warm.

Wort aeration? This batch was aerated normally, but I really don’t know much about how much oxygen is in my wort. I used oxygen and a stone, and gave each fermenter a 90-second blast after filling. Should probably spend some time thinking about this a bit more.

Yeast pitching rate? A good rule is to multiply the propagation volume by 8–15 to determine how much wort can be pitched. Lagers are toward the 8x end of the range and ales towards the 15x end. Three liters x 15 = 45 liters of wort. This batch was 50 liters; maybe a bit on the low side but probably not too low. No microscope . . . how can I ball park the pitch rate? I have read that propagated yeast that is aerated through a cotton plug in the top of a stirred flask (magnetic bar and stir plate method) normally provides 100 million cells/mL (1 x 10⁸ cells per mL or 1 x 10¹¹ cells/liter). This works out to 3 liters x 1 x 10¹¹ cells/liter ÷ 50 liters = 6 x 10⁹ cells/liter = 6 x 10⁶ cells/mL = 6 million cells/mL. Pitching rate looks good. Note to self: Brush up on using scientific notation.

Fermentation normal? Nothing odd. Room temperature constant during fermentation, and no big weather swings.

Strain particulars? White Labs website indicates this strain works best between 68–73 °F (20–23 °C) range and usually attenuates beer in the 70–75% range. The original gravity (OG) was 1.061, so the expected FG is in the 1.015 to 1.018 range based on attenuation range from the web. Could lower fermentation temperature be causing issues?

Known final gravity (FG)? According to what I just calculated the FG should be in the 1.015–1.018 range and the recipe is telling me 1.012–1.018. That’s a little funky.

I don’t know how most people go about troubleshooting, but the linear approach above is how I go about thinking through brewing problems. These items from above stand out: Enzyme dilution, wort aeration, fermentation temperature, and the target final gravity.

When adjuncts like flaked oats are used, it is important to think about enzyme dilution. Most New England IPAs contain about 30% adjunct (calculated as portion of total wort extract), use North American 2-row base malt, sometimes contain malted wheat, and may contain a splash of higher kilned pale malt as a flavor boost. Calculating blended diastatic power (DP) and dextrinizing units (DU) is easy if malt analyses are available. This question does not have enough information to calculate a weighted average for DP and DU, but a good rule of thumb for North American malt is that adjunct ratios up to about 25% are no problem at all. If a good dose of wheat malt in the 10–20% range is used, bumping the adjunct ratio up to 30% rarely causes a problem because wheat malt is usually more enzymatic than barley malt. One problem that flaked adjuncts can cause is starch extraction after mash-off because not all flakes easily yield their extract. For this reason, a cautious method is to skip mash-off and delay kettle heating until the kettle is about 80% full. Both of these steps extend the brew day, but starchy wort is one cause of reduced fermentability.

Wort aeration is a topic that interests me as a practical brewer because it has a very real influence on yeast growth, fermentation rate, and beer flavor, but is rarely measured by the majority of brewers because dissolved oxygen meters (DO) are relatively expensive and measuring DO in wort is not required if aeration or oxygenation is consistently performed. This is pretty easy to do when a controlled volume of tiny air or oxygen bubbles is added to cool wort. And the easiest way to measure gas flow rate is with a rotameter. Although these gadgets are easy to find and are not expensive, few homebrewers measure air or oxygen flow and, instead, rely on time. Flow rate through a stone can easily change as a stone becomes fouled with protein and hop resins, making control by time approximate. High finish gravities can definitely be related to wort aeration.

Fermentation temperature is a red herring for most fermentations because cool fermentation temperatures typically do not result in high final gravities, they just slow the rate of fermentation. Most ale strains have no problem fermenting in the 61–64 °F (16–18 °C) range, especially when a healthy pitch rate is added to well-aerated wort.

Target final gravity is the last item on my list of possible problems, and is really the problem I most suspect. Recipes and yeast profiles provide little more than an educated guess about the final gravity of the batch of beer a brewer brews using another brewer’s recipe with a yeast purchased from any number of reputable sources because the final gravity is a function of wort carbohydrate spectrum coupled with yeast strain. Even when the same beer is brewed in the same system, variations in the FG are not uncommon. Wort carbohydrate spectrum is influenced by grist bill and the specific characteristics of the grains used, malt milling, brewing water chemistry, mash time and temperature, sparge temperature, and wort temperature in the kettle during wort collection. There are definitely lots of things that can influence wort fermentability from a single recipe.

The only way to know the true target FG is to perform a forced-fermentation test where an excess of the fermenting strain of yeast is added to a sample of wort from the brew in question, and the fermentation accelerated in a stirred flask. The American Society of Brewing Chemists (ASBC) forced fermentation method specifies adding 1 gram of compressed yeast to 250 mL of wort and allowing the fermentation to complete, as determined by consistent gravity readings measured over a 3-hour (minimum) time period. Many commercial breweries, especially those that bottle condition, perform forced fermentations on every single batch.

You suggested in your question that adding more yeast may help. This is a very helpful method when you know for certain that your fermentation has not finished. I think kraüsening is the best way to add yeast to a stuck fermentation because adding yeast at high kraüsen helps ensure that the yeast will quickly finish the fermentation, mop up acetaldehyde and diacetyl, and be done. Simply adding more liquid yeast that is not metabolically up and running will not have the same effect as adding yeast in high kräusen.

Diagnosing problems on paper is difficult, but my bet is that you have a combination of factors leading to a higher-than-expected FG, coupled with perhaps inconsistent wort aeration, that has resulted in three fermenters of wort from the same batch ending at different gravities. If that is the case, kräusening should be considered.

Q
My favorite beer is a banana-forward, slightly sweet German hefeweizen (Franziskaner/Paulaner). I’ve tried brewing this style three times and every time my beer has come out bland and flavorless. I’ve tried all the tricks, open fermentation, no oxygen, no starter, using Wyeast 3068, and mashing at 152 °F (67 °C). Should I try a higher mash temperature to get more body and more flavor? I simply can’t get this one right. Help!
Travis
via BYO Live Chat 

A
German-style hefeweizen is one of my favorite styles of beer, and is a beer type that I feel pretty darn comfortable brewing, with two Great American Beer Festival medals in 2006 (gold) and 2008 (bronze) to boot. I tend to avoid style and recipe questions for this column, but this great style is one that many brewers seem to struggle with brewing. I am hoping that my tips help you.

The first bit of advice I have to offer is to keep recipes simple. Most hefeweizens have a grist bill that are about 40–50% malted barley and 50–60% malted wheat. I like adding about 2% dark crystal malt for a little color and just a small kiss of crystal sweetness. I am a fan of reverse osmosis (RO) water and target 100 ppm calcium in the brewing water from a blend of calcium chloride and gypsum. German hops are my go-to for this style and I like using two additions during the boil and a very small addition at flame-out for just a hint of hop nose. Bitterness is low at 12–15 IBU.

I do not believe there are any tricks or secrets to brewing a good hefeweizen, but there are a couple of techniques that I feel are very important. And the most important technique to me occurs at the very beginning of the brew day with a mash rest around 113–126 °F (45–52 °C). This temperature range allows for cytase activity and an increase in ferulic acid levels in the wort. Weizen yeast are so-called POF+ (phenolic off-flavor positive) because they have an enzyme system that converts ferulic acid to 4-vinyl-guaiacol during fermentation, imparting a clove-like aroma to the beer. My favorite weizens have a nice balance of clove and banana and this low temperature mash rest is a great way to ensure a nice punch of clove. Rests at 140 °F (60 °C) and 158 °F (70 °C) follow, with mash-out at 168 °F (76 °C) before starting wort collection.

The next critical step is preparing for fermentation. I have never tried starving weizen wort of oxygen or pitching at a very low rate, and have had success using typical aeration levels and pitching rates. I am picky about yeast strain selection and strongly suggest changing strains if you are not getting the aroma profile you like from Wyeast 3068; this is one of many nice weizen beer strains, and is definitely not the common factor of all great weizens. Since I like a nice clove profile in my weizen, strains that lean a little more towards the phenolic end of the spectrum are more my speed than the big banana bombers. A great way to select a strain is to brew a batch and split it 4–5 ways so you can trial 4–5 yeast strains. Find the yeast strain that is going to give you the aromas that ring your bell.

I suggest fermenting in the 64–70 °F (18–20 °C) range, allowing for a couple days for a diacetyl rest and cold crashing before bottling or kegging. Most weizen strains are true top-croppers, meaning that the yeast rises to the top of the fermenter where it can either be skimmed for re-use or the beer can be racked from beneath the yeast before cold crashing; the yeast that ends up on the bottom of the fermenter can then be collected and reused. Weizen yeast that is harvested in this manner can be used for many generations as long as it is not stored long between brews. Although carbonation level for this style is not likely to move the needle for thin, blah brews, tasty weizens certainly benefit from above average carbonation levels and proper weizen glassware. Prost!

Q
I Just bought some all-grain kits with the priming sugar included. I keg and force carbonate so I now have a box full of priming sugar packets. I just thought, why not add the sugar during the boil. Any drawbacks to this plan?
Rudy Brooks
Junction City, Kansas

A
Rudy, I like your ideas! This question reminds me of lyrics from The Clash tune “Rudi Can’t Fail.”

Now we get a rude and a reckless
We been seen lookin’ cool an’ speckless
We been drinking brew for breakfast
Rudie can’t fail

Not saying you have been drinking beer with breakfast, but the idea of saving up priming sugar bags from kits you have brewed does seem like the sort of idea that could come from pre-brew day planning! So, is this idea fraught for failure? Certainly not. 

Simple sugars are a useful brewing adjunct when you are looking for a gravity boost to simply boost strength or to turn down that flavor dial a tick. No matter what may be said about this agenda, many brewers are not squeamish about adding sugar to wort to enhance beer flavor. That’s right, enhance flavor. Adding simple sugars to a moderately high gravity wort can help develop aromas and flavors in beer, help to balance malt fullness in the finish of a beer, and can bump the alcohol content without drawing unwanted attention. And you can also use simple sugars to reduce beer color, and to reduce wort FAN, and protein levels.

Styles that you may want to brew using your booty of priming sugar include British-style pale ales, West Coast-style IPAs, Belgian-style tripel, North American-style lagers, and Tropical-style stouts. And if you want to work on a GABF Pro-Am recipe for something called “Rudy Can’t Fale,” the name is yours for the taking!

Written by Ashton Lewis