10G Brewing

A big part of getting back into brewing has been a brewhouse upgrade from 5 to 10 gallons. Being able to brew 10 gal at a time means brewing less often but also changed my brewing process significantly.

My reverse osmosis system holds only about 5 gal water, which means brewing 10 gal batches requires water collection to start at least one day before brewday.

My current set-up consists of two 15 gal MoreBeer SS brew kettles. I liked the price and the wide bottom of these kettles. I don’t quite like how high the drain is off the bottom, but that can be mitigated. They also don’t have fill level markings and I need to use a calibrated dip stick for that.

Mash rest with blankets for insulation

Mash rest with blankets for insulation

Just like a German 2 vessel brewhouse, one kettle is used as mash-tun/boil kettle and the other is the lautertun. Covered with a few blankets, a 15 gal mash holds its heat surprisingly well and direct firing the mash-tun allows for efficient temperature adjustment and step mashes. The thick bottom of the kettles greatly reduces the chance of burning the mash even if it is not constantly stirred. The drawback of this set-up is transferring the mash to the lauter-tun. The mash transfer requires scooping most of the mash out of the mash into the lauter tun and then pouring the rest once I’m able to lift the kettle.

Batch-sparging had to give way to fly-sparging. During the first batch I tried batch-sparging, but mixing sparge water into the grain over a false bottom with a huge dead-space, was just not working. It was impossible to get the mash well mixed and the grain. The sparge water is now carefully added in batches and allowed to percolate through the grain. The amount of sparge water is calculated to achieve the desired pre-boil kettle volume. For a while high drain position left a significant amount of wort behind. This was fixed with a barb on the inside and a hose that lays on the lautertun bottom.

Hose on the inside of the lautertun to maximize wort collection.

Hose on the inside of the lautertun to maximize wort collection.

False bottom of the Morebeer 15 gal Brewkettle.

False bottom of the Morebeer 15 gal Brewkettle.

Lautering the mash.

Lautering the mash.

I can easily get 90+% efficiency into the kettle for most beers, which means that sparging must happen evenly and it does not take much longer than running wort through the braided hose of my 5 gal cooler set-up.

The 5 gal brewing process relied heavily on the fact that I could lift the mash, set it aside and use the burner to heat sparge water. That is no longer possible and at least 2 burners are needed, A second burner heats the sparge water in a 15 gal Anvil kettle, which also serves as fermentation vessel.

Where there was an immersion chiller, there is now a plate chiller. An immersion chiller still works for 10 gal batches, but I always dreaded standing over the pot and moving the chiller around. The immersion chiller never brought the wort to pitching temperatures anyway. I needed to lift it into a large tub with ice water for the final chill. A single stage plate chiller doesn’t do that either for me and I’m a bit disappointed about the performance of the plate chiller though. With a reasonably slow wort-flow and a good amount of water the wort temperature drops to only about 40 C (100 F). To get to pitching temperatures I need to float a sanitized bowl or pot filled with ice in the wort.

The wort chilling set-up is sanitized by recirculating hot wort at the end of the boil for a few minutes. After that the wort keeps recirculating but with the water turned on and the wort is allowed to cool do about 90 C (195 F) before whirlpooling it. This lower whirlpool temperature provides less DMS formation and likely better retention of hop aroma for whirlpool hops. The high drain port meant that lots of wort was left behind in the kettle unless the kettle was tipped slightly towards the end. A small stainless steel elbow attached to the drain port from the inside of the kettle mitigated this problem without noticeable interference with the whirlpooling action. A whirlpool stand was not needed for immersion chilled 5 gal batch and adds about 20-30 min time. It does provide a welcome opportunity for late hop additions.

Wort chilling set-up with pump and plate chiller.

Wort chilling set-up with pump and plate chiller.

Trub cone in the boil kettle. To the left is the stainless steel elbow that is attached to the spigot from the inside.

Trub cone in the boil kettle. To the left is the stainless steel elbow that is attached to the spigot from the inside.

Even with moderate wort flow rate and lots of water, the wort temperature drop only to about 40 C (100 F).

Even with moderate wort flow rate and lots of water, the wort temperature drop only to about 40 C (100 F).

Steam sanitation of the HLT which is also used as fermentor.

Steam sanitation of the HLT which is also used as fermentor.

The 15g Anvil kettle, that is used as fermentation vessel, is steam sanitized after it is no longer needed as HLT. Steam sanitation is very practical since it can easily kill microbes hiding in cracks of the spigot. But don’t forget about it, boil off all the water and ruin the kettle. Only about a liter of water (or even less) is needed to fill the kettle with 100 C (212 F) steam for about 5 – 10 min.

Having a kettle with spigot as primary fermentor allows for easy skimming of the kraeusen and makes transfer to kegs for secondary fermentation really easy No more starting a siphon. Just attach a hose and open the valve.

Brewing 10 gal batches means twice the amount of beer for one brewday, but not necessarily the same brew time. My 10 gal brewdays are taking longer than my 5 gal brewdays used to. Most of that is because 10 gal batches are slower to heat and transfer than 5 gal.

Low Oxygen Brewing

In the past weeks two of my followers have pointed me to a paper released by the folks from the German Brewing Forum. That paper talks about low oxygen brewing and how very low oxygen levels (so low that even very detail oriented brewers will have to change their brewing technique to achieve them) are responsible for what we have been calling the Elusive German Flavor in beer. That delicate malt flavor with a subtle background of fresh hops.

I myself have not been able to test any of this but am very intrigued to do so after reading through the paper. The main points are that one needs to deaerate the strike and mash sparge water, use sodium metabisulfite as an additional scrubbing agent and be very careful with doughing and any oxygen uptake later during the brewing process. A DO (Dissolved Oxygen) meter helps with keeping track of the O2 levels throughout the process.

If you think this is the HSA (Hot Side Aeration) discussion all over again, you are somewhat right with the caveat that there is new evidence and a new theory. This theory postulates that the current standard home and craft brewing process already allows for enough oxidation that additional splashing of the wort does not do any noticeable change. As a result HSA experiments have shown inconclusive results so far.

I have heard that this started to spark controversy and I can see that. If the authors are correct, and many seem to have been able to repeat the results, brewers will have to take a closer look at their brewing process and possibly equipment if they want to achieve these results. But keep in mind that not all types of beers are expected to benefit from this. There are many excellent beers, especially craft beers around the world, that are brewed in conventional brewhouses without a low oxygen process.  It’s more along the lines of decoction where an more elaborate brewing process is used for some beers to achieve the desired flavor profile.

At this point we have something new to try and to look into and need to see how this develops over time. Especially as these beers are showing up in competitions and we can see less biased results.

An anecdotal observation that supports this is that craft brewed beers in Germany (usually brew pubs) lack that delicate flavor that many commercially brewed beers in Germany have. Those commercially brewed beers are more likely brewed in a low-oxygen brewhouse.

Here is a link to the paper: On Brewing Bavarian Helles: Adapting to Low Oxygen Brewing


This all started when I was preparing one of my presentations for ANHC-3 and I looked into the patent for Boston Beer Company’s Infinium and other patents for high attenuation beers. I found that an enzymatically active malt extract (basically wort with active b-amylase enzymes) can be added to the fermenter. I was skeptical about this approach since malt is full of beer spoilage organisms (which is why you should not handle or mill malt in your fermentation area) and brewers rely on boiling to kill these organisms. However, boiling would also denature all the enzymes. According to the patent I found holding the mash for 30 min at 60 C before pulling the enzyme extract should be enough to kill the microbes but preserve enough b-amylase to be a useful in the fermenter.

So when I had a low fermentability Weissbier I gave this a try in a small test fermentation. Here are the two blog posts on that topic

The result was that I did not spoil the beer and that the enzymes in wort don’t break down as much of the residual sugars, and possibly proteins, as Beano does. Based on these results I was planning to use this technique on a full 18 l batch.

Since I expected close to 100% apparent attenuation it had to be a big beer. High attenuation and thus lighter body works well with a Double IPA. In fact many brewers of good DIPAs use sugar as an adjunct to add alcohol without adding body. So I brewed a stronger version of my KaIPA using this recipe: KaIPA^2 on Brewer’s Friend. It uses lots of my homegrown Cascade hops and hop extract for the bulk of the bittering.

Key was an initial mash rest at 60 C for 30 min and then filtering some of that mash to collect about 500 ml enzymatically active wort. That wort was cooled immediately and used to wake up the yeast. Using it to wake up the yeast was not necessary but why not. That way the yeast could get a head start and I would not forget to add it later.

When diastatic enzymes are used in the fermenter the wort fermentability set during mashing doesn’t matter which is why I raised the mash temp to 70 C after the 60 C rest. That way conversion was faster. The rest of the brewing process was as usual. To check the spoilage potential of the enzyme extract I took two wort samples from the cast out wort. To one of these samples I added the enzyme extract. Both samples were incubated at about 20 C to perform a wort stability test. To my surprise the sample to which I added the enzyme extract showed signs of microbial growth at about the same time as the other sample, which was after 3 days. This means that the enzyme extract did not carry substantial more microbes than the cast-out wort. If you plan to try this technique you may also want to do a wort stability test with and without the enzyme extract.

The fast ferment test for this beer also got some of the enzymatically active wort which is important to get an estimation of the actual attenuation limit of the beer. In this case the FFT stopped at -0.2 Plato which is an attenuation limit slightly above 100%.

To keep the production of higher alcohols in check I started the fermentation at 14 C (58 F) which is fairly low for the used yeast (WLP 001 – American Ale). After a few days I raised the temperature to 16 and then later to 20 C. The production of higher alcohols happens when the yeast consumes wort amino acids and that only happens during the growth phase which is generally over once high Kraeusen has been reached.

8 days after pitching the beer reached 5.0 Plato (down from 19.6 Plato). I let it go for another week in the primary fermenter before I transferred to a keg with some of the yeast. Later, after some more fermentation in the keg, I added gelatin and put the beer on tap. I was a bit lazy with taking more detailed notes.

I have been enjoying this beer for the last 2 weeks. The actual fermentation reached only 2.1Plato (an attenuation of almost 90%) which is higher than I expected based on the fast ferment test and the next time I’ll have to let the beer ferment longer. Unfortunately this IPA wants to be enjoyed young and 30 days after brewing the hop character is starting to fade. I still have the option of dry hopping in the keg which I may want to do.


OE: 19.6 Plato

AE: 2.1 Plato

ADF: 90 %

ADF (limit): 102 %

ABV: 9.6 %

IBU: 54 (Tinseth estimation)

beer pH: 4.30


Tasting notes:

Because of its high attenuation the beer has the mount feel of a Pale Ale but the high alcohol is evident both in aroma and taste. The hop character is fading but I have not added any dry hops yet since I was hoping to be able to rely on the 30 min hop stand with about 40 g of whole flower cascade hops.

Future improvements:

There are a number of things I want to improve in the future. On top of the list is to get the yeast to ferment closer to the attenuation limit. That probably means more yeast, possibly with some O2 during fermentation, and longer primary fermentation time. I think 95% attenuation is a reasonable target. To keep the current mouthfeel of the beer at 95% ADF I want to use a substantial portion of wheat or rye malt in the grist. Wheat malt would provide protein and rye malt would add b-glucans. Neither of these compounds will be attacked by the enzymes and should provide an upper limit for the attenuation.

This experiment was a definite success. The beer is a high gravity beer that is very enjoyable. Any concerns I had about adding non boiled wort to the fermentation were not justified. I also did not produce the dreaded “rocket fuel” that many brewers seem to get when they use enzyme preparations like Beano. I encourage others to give this a try.  Maybe this will become an accepted method of brewing DIPAs that are extremely or even too drinkable for their alcohol content.


A New Mash Chemistry and Brewing Water Calculator

When I started helping Brewer’s Friend as a technical adviser I couldn’t help but notice that the mash pH predicted by its brewing water calculator was way off. Since I have done extensive work on brewing water and mash chemistry already I took this as an opportunity to develop a new Mash Chemistry and Brewing Water Calculator from scratch. The goal was to build something that provides a simple and intuitive user interface yet implements the underlying chemistry to at a level of accuracy that is generally not done in brewing water calculators. In fact the only calculator that goes to that extent is A.J deLange’s NUBWS (Nearly Universal Brewing Water Spreadsheet).

Since Brewer’s Friend is an online recipe calculator the new calculator would also become an online tool. This worked very well in its favor since it is very cumbersome to model complex systems in spreadsheets. PHP, or any other programming language for that matter, makes that type of modeling much easier. In addition to that modern web browser technology makes it simple to create dynamic forms that can readily adjust the form to only asking the user for information that is actually needed based on the context.

That was 3 months ago and after many long nights of coding, re-coding, testing and even running more mash pH experiments version 1.0 has finally been released and is available on Brewer’s Friend.

When you first open the calculator it presents itself like any other basic water with sections for source water, salt additions, grist, mash pH and final water report following this flow chart:

Flow chart for basic use of the calculator

Flow chart for basic use of the calculator

But that’s not all. For those who need want to do more complex water treatment calculations, the full flow chart looks more like this:

Full flow chart for brewing water and mash chemistry calculator.

Full flow chart for brewing water and mash chemistry calculator.

All these additional section are hidden by default and can be shown on demand.



The first release features makes these features available:

  • Blending of two water sources
  • Bicarbonate/carbonate content can be set from either alkalinity or bicarbonate. pH can also be entered for increased accuracy
  • Electrical balance (ion balance) of the source water
  • Simple GH&KH measurements can be used as a crude way of specifying the source water.
  • Report of basic and advanced water parameters of the source water. Among the advanced properties are temporary/permanent hardness and CO2 partial pressure
  • supports all major salts (including magnesium chloride) as well as the hydroxides slaked lime and lye
  • Alkalinity reduction through boiling and slaked lime. These are features that rely on a more accurate implementation of the water’s carbo system
  • Wide range of supported acids including the less commonly used citric, tartaric and acetic acid.
  • Salt and acid additions can be made to all water or only the strike (mash) water
  • A different water source can be used for sparge water. In most cases that might be reverse osmosis water when the tap water is suitable for mashing.
  • Salt additions to sparge water or kettle
  • Sparge water acidification with a wide range of acids.
  • Detailed report of the treated mash water
  • Support for undissolved chalk.
  • Grist pH properties can be estimated from beer color or malt bill
  • Mash pH prediction based on balancing the various weak and strong acid systems that might be present (carbo system, weak acids and grist)
  • overall water report based on the mash and sparge water profile
  • target water comparison of the overall water report

For now this tool is only available as a stand-alone calculator but Brewer’s Friend is planning to integrate it into the recipe editor. This will eliminate duplicate entry of the beer’s malt bill. It will also allow the user to use saved source water profile(s).

Go ahead and give it a try. If you have feedback, positive or negative, please let me know:

Mash Chemistry and Brewing Water Calculator

In subsequent posts I’m planning to write more about some of the discoveries I made while writing this tool and how it’s mash pH prediction does compared to actual mash pH data that I have.


Improvised Fermentation Temperature Control

As luck will have it, both the freezer chests I have been using for lagering and primary fermentation are broken and I have to get new ones. They have been running well for more than 5 years and started failing within 2 months of each other.

Currently my basement is at ~14 C and fermentation control for ales is as simple as a heating pad and a temperature controller. The probe is strapped to the carboy or placed into the bucket with a thermowell. The heating pad is placed underneath the fermenter. But lagers are a bit more challenging since I need to get them below ambient temperature. After some thinking I came up with this setup that uses equipment I have available. I doubt that I’m the first one to do it that way and I think Basic Brewing’s Low Cost Lagering approach works like this:

Simple setup for fermentation control.

Simple setup for fermentation control.

The carboy sits in a tub of  water and a submersible utility pump (the same pump I use for my carboy washer) pumps water through my immersion chiller. That chiller sits in my mashtun filled with snow slush. The pump is controlled through a temp controller connected to a probe sitting in a glass thermowell which reaches into the water in the tub. This setup work very well for me but here are a few thoughts and concerns:

  • Don’t let the ice or snow melt completely. If the pup ends up running continuously, because the water is not cooled, it will actually warm the water through its own heat. Initially I had the ice in a plastic bucket and it melted pretty quickly. After putting it in the MLT I only have to top it off once a day. The MLT has the added benefit that I can easily drain the melt water.
  • Since I have stick-on thermometers on my carboys I can’t submerge them completely. Before fermentation starts this can cause  temperature stratification and result in the top of the beer starting fermentation a higher than intended temperature. Next time I’ll put the carboy into a large trash bag which should allow me to submerge the carboy more completely.

I drape the blue blanket to cover the whole set-up and keep out the light.


Another Doppelbock and oxygen tasting experiment

I finally got around to taste 4 bottles of my last Doppeblock that were treated differently with respect to yeast and oxygen. All 4 were bottled on 8/18/12 straight from cold conditioning (which lasted about 2 month) using a picnic tap and short racking cane. At the time of tasting they had been in the bottle for 4 month and 2 weeks.

The bottles received this treatment:

  • “no yeast/no O2” – did not receive additional yeast or O2
  • “no yeast/O2” – got a shot of O2 in the headspace shortly before capping
  • “yeast/no O2”  – received about 0.5 ml of WLP 830 yeast slurry and no O2
  • “yeast/O2”  – both yeast and a shot of O2

I did a tasting between  “no yeast/no O2”  and  “no yeast/O2” bottles 2 months ago. The results can be found here: Better Foam Stability Through Oxydation?. During that tasting I observed a distinct difference in foam stability that many readers contributed to a poorly cleaned glass. This time I made sure that the glasses were perfectly clean. That meant soaking in diluted vinegar to remove lime stains, washing with dish sop and a RO water rinse.


The 4 beers that were tasted. From left "no yeast/no O2", "no yeast/O2", "yeast/ no O2" "yeast/O2". The picture was taken during the foam stability test. The two samples on the right were poured 1 min after the samples on the left were poured.

The 4 beers that were tasted. From left “no yeast/no O2”, “no yeast/O2”, “yeast/ no O2” “yeast/O2”. The picture was taken during the foam stability test. The two samples on the right were poured 1 min after the samples on the left were poured.

Here are my tasting notes. When I refer to “dark beer aroma/taste” I mean the type of aroma/taste one gets from a good Doppelbock. Think of dried fruit mixed with black currant. I’m also listing pH, refractometer reading in Brix (I didn’t feel like taking hydrometer readings and the foam stability number* )

  • #1 – “no yeast/no O2” –  nice “dark beer aroma”. The aroma intensity is about the same as #2. (pH = 4.72, 10.4 Bx, foam = 5:30 min)
  • #2 – “no yeast/O2” – I made a note that the aroma is slightly stronger than #1, but than I made an opposing note on #1. I cannot conclude that it was objectively stronger (pH = 4.72, 10.4 Bx, foam = 8:30 min)
  •  #3 – “yeast/ no O2” – noticeably higher carbonation that #1 and #2, noticeably less of the dark beer aroma/flavor that #1 and #2 exhibit. Thinner mouthfeel than #1 and #2 (pH = 4.72, 10.1 Bx, foam = 10+ min)
  • #4 – “yeast/O2” – noticeably higher carbonation that #1 and #2, slightly less aroma than #3 (not confirmed in blind tasting), similar taste to #3 (pH = 4.68, 10.0 Bx, foam 10+)

After this tasting I did a blind tasting where I poured 2 glasses of each beer, scrambled the total of 8 glasses and attempted to match them to their respective beers. This is the groups I ended up with

  • group 1: one of #1 and one of #2
  • group 2: one of #1 and one of #2
  • group 3: one of #3 and one of #4
  • group 4: one of #4 and one of #3


This experiment solidifies the theory that the presence of yeast slows the development of the typical Doppelbock flavor. It does not show that the addition of oxygen, which is presumed to be the cause of this flavor, enhances this flavor of the beer after 4.5 months of aging. After 2 months of aging there appeared to be a more noticeable difference  (see  Better Foam Stability Through Oxydation?) At 4 months the addition of Oxygen did not make as much of a difference as the presence of yeast. This became apparent in the blind tasting where I could not keep the O2/no O2 versions apart but was able to identify the yeast/no yeast versions.

In future batches I do want to expand this experiment to developing a time line that shows when the “Doppelbock” aroma starts appearing depending on treatment. Maybe it makes sense to add O2 to 1/3rd of the bottles, no O2 and no yeast to another 1/3rd and yeast to a 3rd. This may allow brewers to control when the flavor/aroma of a Doppelbock (or other strong dark beer) peaks. An aspect that is very important for competitions.

It also shows that the beer was not completely fermented. Hence the continued fermentation when yeast was present which lead to higher carbonation and a lower refractometer reading.


* when I determine foam stability I take a Koelsch glass and pour the beer straight down the middle until the foam reaches the top.  The foam stability number is the time it takes until the foam opens up and the surface of the beer can be seen. Anything above 7 min is really good. Below 4 min, there is a problem with the foam stability.

Incubator built

If possible I try to keep my brewing stuff out of the house and in the basement. But that has been challenging in the winter when it is only 15 C (60 F) and I’m trying to propagate ale yeast. What I needed to build was an temp controlled enclosure and I was planning this for a while but never got around to getting started until I saw a cabinet on the side of the road that would be perfect.

The completed incubator. It's hanging a bit high, but I wanted it out of the way since my fermentation room is not all that big.

All I had to do is to cut off the base, line it with insulation, install a PID and outlets.  Two of which are controlled by the PID and the others are always on. I got the PID a while back on Ebay. It is holding the temperature steady but somehow the temp probe seems to be off by not only an offset but also by its slope. Unfortunately there is very little documentation on this unit. I simply added another digital thermometer to check the actual temperature.

The inside, showing the outlets and the heating pad

PID and back-up thermometer. I don' fully trust that the PID is showing the correct temperature. But it is holding the temperature steady.

Heat is provided by a heating pad that doesn’t have automatic shut-off. I plan to use two heating pads to cover the bottom once I found a suitable grate that keeps the flasks and stirrers suspended above the heating pads.

Estimating yeast growth

Recently there has been a lot of focus on yeast growth calculators for starters. But most of the various calculators out there base their data on work published in Chris White and Jamil’s yeast book. Unfortunately the yeast growth example given in that book was only for a non agitated starter. When a starter is constantly stirred all the yeast is kept in suspension in a homogeneous nutrient environment. That is not true for non agitated starters where yeast will sediment and only evolution of CO2 will cause agitation. As a result stirred and still starters are expected to show different growth behavior that cannot be simply approximated by adding a constant scaling factor to yeast growth.

Jamil’s pitching rate calculator supports stirred starter fermentation but the growth curve used for that mode is a simple scaling of the growth curve for non agitated starters. Jamil never published how he arrived at the model used in his calculator. As a result I have to draw conclusions based on what I can observe when I run data points through his calculator.

Before I get into comparing growth curves, I need to explain how I look at yeast growth. The primary factor in yeast growth is the available sugar. Within a practical range of wort concentrations the actual concentration of wort will have little impact on yeast growth. I’m still going to test this in a controlled experiment but observations from yeast propagation in my brewing seem to support that. Because of that I focus not not how many Million yeast cells are in a ml of wort, but rather how many Billion yeast cells get to share a gram of extract (sugars, proteins, minerals, etc) that is dissolved in that wort.

As for yeast growth, I care about how many new cells of yeast can be grown from that gram of extract. In their yeast book Chris and Jamil use a yield factor defined as new yeast growth in Million/ml per degree Plato drop of apparent extract. This takes into account that different worts can have different attenuation levels and with it varying amounts of fermentable sugars. While this is correct it requires knowledge of the wort’s fermentability and most brewers don’t know the fermentability of their starter wort. Furthermore the uncertainty of starter wort fermentability is likely +/- 5 % and this is well within the imprecision that one can expect from yeast calculators. I expect yeast growth calculators to have an error of +/- 15% or more. Because of that I feel confident in using Billion cells growth per gram of extract (B/g) as the yeast growth metric that should be tracked. Assuming a starter attenuation of 75%, the conversion factor between  “yield factor” and specific growth (B/g) is 13.3:

1 B/g = 13.3 M/(ml*P)

Now that I established how I plot yeast growth I can show some charts.

This one compared Mr Malty data for simple starters and stirred starters with the simple starter data from the Yeast book as well as a 2.7x scaled version of the simple starter data:

It is apparent that the growth curve for simple starter matches the data from the book, which makes sense. What surprises me, however, is that the stir plate data is not just scaling the yield for a given innoculation rate, but it also scales the inoculation rate. This means that the yeast growth calculator has different optimal innoculation rates for simple and stirred starters. That is something I don’t follow and my data contradicts that. More on that in a moment.

The following is a chart with my data. I have been using WY2042 since it is a low flocculant lager strain. Most of that has been presented in a previous blog post (Yeast growth experiments – some early results). What’s new is the non agitated data points and a few data points for using yeast that was stored in the fridge for 5 days before being used.

When the data is potted as growth in billion cells per gram over initial billion cells per gram, the data makes more sense. As the amount of extract available to each cell of the starting population approaches the amount of extract needed to grow a new cell, the growth per extract starts to fall. This is because the initial population is in a resting state and when sugar becomes available all vital yeast cells start to consume the sugar. A cell will not start budding unless it consumed all the resources needed to grow a new cell. If this was an ideal culture, where every cell consumes sugar at the same rate and needs the same amount of sugar to grow a daughter cell, cell growth would stop once there are more cells per gram of extract that it takes to grow the same amount of cells. This is because none of the cells would have access to the amount of nutrients needed to grow a new cell. But this is not such an ideal culture and some cells will consume nutrients faster than others and will be able to grow daughters while others can’t.

I also expect that yeast growth of a large population of older cells is reduced compared to young cells since the old cells will need to fill their reserves before they can start accumulating nutrients for growth. I don’t have enough data on that yet to quantify this effect.

This effect of dropping yeast yield is not as pronounced for a non agitated culture. This is because in such a culture not all yeast cells have the same access to wort nutrients due to sedimentation. Yet another reason why one cannot estimate the yeast growth characteristics in a stirred starter from a non agitated starter.

Based on my observations and knowledge of yeast growth so far, I think the following yeast growth model should be used for calculating expected yeast growth in stirred starters:

If (initial cells < 1.4 Billion/gram extract)
  yeast growth is 1.4 Billion / gram extract
If (initial cells between 1.4 and 3.5 Billion / gram extract)
  yeast growth is 2.33 - 0.67 * Billion initial cells per gram extract
  no yeast growth

For non agitated starters a growth rate of 0.4 Billion per gram should be assumed over the full initial cell density range (0 – 3.5 B/g). I don’t think that starters with more than 3.5 Billion cells/g  are practical. I expect the growth rate in starters to be affected by the shape of the vessel, the volume of the wort and more. The 0.4 Billion new cells per gram proposed here is a rough guess based on the data points I have so far.


The proposed model for stirred starters has been implemented in:


Better Foamstability Through Oxidation?

Oxidation experiments, again. This time on the latest batch of Doppelbock. Frequent readers may have seen the earlier posts on the subject of oxidation during Doppelbock aging: The effect of yeast on the flavor development of Doppelbocks and Follow-up on the Doppelbock yeast vs. no yeast in bottle experiment in which I tasted the same batch of Doppelbock with and without added yeast. This year I not only bottle some of the Doppelbock with yeast, but two bottles also has pure O2 added to the head space.

Last night I tasted a version bottled normally and one where I purged the head space with O2. The intend of the O2 in the head space was to see if it speeds up the aging process. Both beers were carbonated at bottling time and free of yeast. This tasting was 2 months after the beer was bottled and 6 1/2 moths after it was brewed.

comparing the color. bottled without oxygen (left) vs. bottled with oxygen (right)

The oxygenated version had a darker color as can be seen on the image on the left hand side and below. This color in crease is a known effect of oxidation and I have also observed this when I oxygenated and force aged a Pilsner. The increased color in the picture was not just because the oxygenated beer had a closed foam cover.

A better picture for comparing color.

But the biggest surprise was the incredibly poor head retention of the normal beer. It annoyed me during attempts to take a good picture for comparing color since the foam cover would quickly break open while it stayed close on the oxygenated beer. The shadow of the foam skews the color and darkness of the beer.

So I took another set of glasses and performed my standard foam stability test where I pour beer straight down the middle until foam reaches the top. I did this for both beers and waited for the foam to settle.

Foam stability test. Note the coarse bubbles on the non-oxygenated beer.

Foam stability test only one minute later.

The non-oxygenated beer clearly showed very coarse foam that collapsed quickly. Generally it would take 7 – 10 min between pouring and opening of the foam cover to show beer surface. But for the non oxygen beer it took just about 2 minutes. That was very surprising and I have no explanation for that. An internet search for foam stability and oxidation did not reveal any useful leads. It is certainly possible that something else, other than oxidation, was to blame for the poor head retention. I do have another normal vs. oxygenated pair and plan to taste this in a few weeks along with a bottle to which I added yeast.

As for taste, the normal beer did have a slight “dark malt” aroma. It’s bitterness was rather sharp and lingered a bit. The oxygenated version had notes of black currant (common oxidation aroma) and a slightly more pronounced “dark malt” aroma. It did not taste like cardboard or sherry. It had more of the desirable Doppelbock character than the non oxygen version and I would consider it definitely the better beer of the two. It won in both, taste and appearance.


The stark difference in foam stability is interesting and will require attention in subsequent samplings of this beer. The accelerated aging of the oxygen beer was expected. I was just surprised that the beer did not taste oxidized given the fact that it was actually bottled with a head space full of O2. Dark beers are known to withstand oxygen better due to the antioxidative properties of melanoidins.


I took one of the non O2 beers and a carefully cleaned glass and repeated the foam stability test again. This time the foam did not fall that quickly, but it still showed unusually large bubbles. There is a good chance that the glass I used for the test was not clean enough and skewed the results. I’ll try this again when tasting the other bottle with added O2.

Tasting of the enzyme beers

I finally got to taste the experimental beers that were treated with enzymes to fix an unexpectedly low attenuation limit (see Enzymes in the Fermenter).

This was after the beers were allowed to carbonate at room temperature for about 10 days. After that they were stored at about 10 C (50 F) for about 3 weeks.

The control, which had only water added to correct the  OE (original extract) to the same level as the others, had a very full mouthfeel. It did not taste sugary sweet but had a distinct full mouthfeel which did come with some increased sweetness, though. At time of tasting this beer had an apparent attenuation of 76% (final extract was 4.2 Plato)

The beer, to which enzymatic malt extract was added, did not open with a loud “plop”, but did gush and poured with lots of foaming. Looks like there was some additional fermentation in the bottle. The beer had a very nice light body that did not show alcohol hotness or seemed too thin. At time of tasting this beer had an apparent attenuation of 90% (final extract was 1.8 Plato)

The beer which had Beano added did also gush out of the bottle after opening and also poured with a lot of foam. It tasted even lighter than the beer with enzymatic malt extract. But it made the beer thinner than it should be. There were also some sharp alcohol notes, but I would not characterize it as “rocket fuel” either. At time of tasting this beer had an apparent attenuation of a whopping 96% (final extract was 0.8 Plato)

Here are the stats:

control malt extract Beano
corrected starting extract 17.8 17.7 17.7 Plato
Extract 4.2 1.8 0.8 Plato
ADF 76.4% 89.8% 95.5%
Alcohol 7.2% 8.5% 9.0% w/w
pH 4.4 4.37 4.34


The ezymatic malt extract worked very well for this beer. It did not spoil the beer as one would fear when adding non-boiled wort. It also did not go as far as Beano treatment which leaves sufficient residual body. Beano’s glucoamylase seems to be able to break more dextrins than the enzymes that were present in the malt extract.

Going forward I plan to employ enzymatic malt extract treatment in the fermenter on a full size batch. This would work well for a double IPA or an imperial Pilsner.