To this end, I did an experiment to find for myself the effects of over-pitching or under-pitching a beer on my brew system and the results are in this post. This experiment created its own thread over at Homebrewtalk so I wanted everyone reading to get these results. I want to point out, however, that I don’t feel the experiment was a success, although some information was gleaned from the experiment. Here are the reasons why it failed:

1. Beer style. I chose a blonde ale thinking that off-flavors would be more apparent. Differences were actually very subtle.
2. Yeast strain. This is probably the biggest mistake. I chose Wyeast 1056, or Chico yeast, to test. Unfortunately, this yeast is pretty clean and pitching rate changes might not change the yeast flavor profile that much.
3. No oxygen or aeration. I did not oxygenate the wort prior to pitching. I thought the action of sprayed wort hitting the side of the fermentation vessel would introduce enough oxygen but I think I was wrong. Several brewers on homebrewtalk pointed this out and I think they are right. The control beer had a strange off-flavor that was hard to place.
4. Fermentation vessels were not covered. Another big mistake. There was varying degrees of lightstruck, with the control pitch the most affected.

Having said all of this, here is the fermentation profile of the three beers:

I measured the gravity of each beer every 8 to 12 hours using a 200 ul pipette-man. As you can see, the fermentation profiles are exactly what I was hoping for. The over-pitched beer’s rate of fermentation was faster than the control, while the under-pitched beer was slower. One interesting thing to note was the under-pitch beer finished at a lower gravity than the control pitch (1.009 compared to 1.012). I’m not sure what this means and this bears repeating. Could under-pitching give slightly lower final gravities? One speculation is that the yeast are stressed to the point where attenuation is raised.

Once the beers finished bottle conditioning, I had my wife, Kim, set up the samples in a blind tasting for me. I could not pick out the control beer. Actually, I totally missed on guessing which beer was which. The next day, I took all the beers to a yeast class I was teaching at Brooklyn Homebrew yeast and the students could not pick out the beers either. This was my first time teaching a class on yeast for homebrewing, and I went over the 2 hour time limit. I was rushed, due to no fault but my own, and did not tally what people thought of the beers.

However, after knowing which beers were which (I know – not very controlled/blinded) I could taste subtle differences. Hopefully my ability to critique my beer is not subject to suggestion. Here is my take on the three beers, faults and all:

Control-pitch: The nose smelled of faintly oxidized hops and medicinal. Uh oh. Toasty malt background with agressive bitterness that approaches astringent. There is a phenolic, almost plastic-like taste in the backend. I don’t think this is due to contamination as the other beers seem fine. It’s possible that the lack of oxygenated wort and light produced this result. However, cutting through this reveals a very clean beer with the american two-row shining.

Over-pitch: No evidence of phenols. However, the is no evidence of anything. The beer is super clean with a bland malt profile. The beer is thin and almost water-like with very little body.

Under-pitch: The nose of the beer gives away some fruiter ester that lingers and disappears. The taste has an odd assortment of esters that clash with the malt and make the beer quite unpalatable. This beer had a thicker body (although slight) compared to the control. The ester profile, although not strong for Wyeast 1056, reminded me over-ripe peaches.

Conclusions: As a scientist, I would have to say these results are pretty much inconclusive since my control did not work. However, the over-pitch beer was cleaner and thinner while the under-pitched beer had some strange esters going on. This would seem to back what other people have seen about pitching rates: over-pitching produces a bland beer, while under-pitching produces a stressed beer with esters being produced from the yeast.

Future: I plan on teaching another class at Brooklyn Homebrew on February 26th and plan on repeating this experiment in the coming weeks. My presentation will be more streamlined and more time will be given to the students to sample and critique the beers – more data for the experiment. Also, a few posters on homebrewtalk have asked for the presentation slides. I will post them on February 26th after revising them for my next class. The next experiment will be a characterful English Bitter and I will use an expressive english ale yeast. I may also increase the over-pitch rate to exacerbate any results. I will also try assess head retention in each condition. Once the experiment commences I will post here and on homebrewtalk. Hopefully, this will be the last word (at least for me) on pitching rates.

To recap, I diluted the dregs to get single colonies plated on regular MYPG agar but I saw no growth. I then plated straight dregs form the bottle and also saw no growth for two weeks. I found this to be strange since an earlier experiment with Lou Pepe dregs at least grew coliform bacteria. I then decided to inoculate a very small amount of Blabåer sediment into 10 mls of sterilized wort and after four days in a shaking incubator I saw growth.

I plated what grew onto three different selective agar:

1. WLN media – allows for the growth of anything
2. WLD media – contains cycloheximide which blocks S. cerevisiae growth, but not Dekkera/Brett
3. MYPG + Bromocresol green - S. cerevisiae  will not metabolize the dye and colonies will look green.

Check out the Wild Yeast Project main page to see the preparation and controls for the above mentioned growth mediums.

Here are my results:

WLN media

WLD media

MYPG + Bromocresol Green

A couple of important things to note. First, the wild yeast that grew did not obey the selective media similar to Brett B and Brett L. Specifically, this yeast grew less under cycloheximide selection and did not metabolize the dye. They looked like S. cerevisie. Secondly, the colonies are almost uniform. This suggests that one yeast strain dominated the wort culture. There is an exception to this however, as one (yes one!) yeast cell grew into a colony that looked different from the others:

Next, I picked two colonies, one normal one and the different colony, and looked at the cells using an 100x immersion oil objective. For simplicity, I named the flower-like colony CB1 and the other colony CB2.

CB-1

CB-2

Conclusions:

These two strains definitely look like wild yeast, especially CB-2. The long cells are reminiscent of Brett L. It is interesting to note that the CB-1 does not have the same cellular morphology (elongated cells) as CB-2 and suggests these are two independent strains. Only PCR to look at genetic markers will identify these strains as different and wild. Another curiosity is why I got no bacteria in this culture but the opposite in my Lou Pepe experiment. Whatever strain(s) this wild yeast is, it outcompeted all other wild yeast and bacteria. Also, the wild yeast isolated behaved just like S. cerevisie. The yeast were largely inhibited by cycloheximide and did not metabolize the Bromocresol green dye. Chad Yakobson of the Brettanomyces project and Crooked Stave has mentioned that non-commercial wild yeast might behave completely different since hardly anything is known about them. For now I’ll consider this a success in isolating wild yeast and brewing a batch of homebrew with this yeast is in my future!

The next step in characterizing these strains are some forced fermentation tests.

This number is important because if you add too little yeast they will tend to grow more, produce more off-flavors such as diacetyl, and not ferment your beer adequately. Adding too much yeast could lead to yeast autolysis flavors, a thin and watery mouthfeel, and lack of desired flavors. There is a sweet spot that all brewers (pro and amateur) aim for to excel in fermentation. Pitching rates are measured in yeast cells per ml per degree of Plato and there are differing opinions as to the ideal number. If you find different pitching rate numbers the most important thing to do is to determine your own pitching rate on your system as this could vary between different brewing systems. An average pitching rate that is cited is:

1 million yeast cells / ml of wort / º Plato

This number can change depending on several factors:

• Ale versus lager. Lagers generally need more yeast to ferment adequately, and the pitching rate could jump to 1.5 million cells/ml/º Plato. Some ales, such as mild ales, may need less.
• Gravity. Higher gravity beers need more yeast to ferment the high concentration of sugars (above 1060). Again, 1.5 million cells/ml/º Plato is a good choice for high gravity ales.
• Fermentor Geometry. Different vessels can alter how yeast grow and ferment. For example, fermenting in a tall cylindrical vessel puts more pressure on the yeast so a slightly higher rate is needed. The opposite would be true in a plastic bucket.

So how do you determine the number of yeast cells to pitch? Lets do some some simple math. Lets say you have a 5 gallons of 1.035 wort and we selected a pitching rate of 0.8 million cells/ml/º Plato. First convert gravity to Plato scale. Divide the last two gravity points by four to get that number:

º Plato = 1.035 gravity / 4

Plato = 8.8º

Next, figure out how many millimeters are in 5 gallons of wort. Since 1 gallon has around 3785 mls that would be 18,925 mls. Now multiply all the numbers together to get your total number of cells needed to ferment the batch of beer:

Cells needed = (pitch rate) * (mls of wort) * (º Plato)

=(800,000) * (18,925) * (8.8)

= 133 billion yeast cells

One important thing I want to mention is the need for a starter. Realizing that we need 133 billion yeast cells for a 5 gallon batch of low gravity beer, the 100 billion cells provided by WYeast packs, for example, is not enough yeast cells to pitch. Lots of homebrewers stick to the rule of “above a gravity of 1.050 is when you make a starter”, but this might not necessarily true and why I always make a starter for my beer. Go by the numbers and not by conjecture.

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Now this is all well and good, but what does that mean for my beer? Personally, I’ve never tasted a beer that was underpitched or overpitched. Will there be off-flavors? If there are, what kind? What will be the kinetics of fermentation? This sort of experiment has been done before, but I really wanted to see the results first hand. Moreover, I will be blind tasting the results at a yeast class that I am teaching at my local homebrew shop, Brooklyn Homebrew.

The experiment will based on the following criteria:

1. Beer style: Blond ale. I chose a blond ale because any off flavors will have little to hide behind.
2. Yeast strain: Wyeast 1056. I had a tough time choosing the yeast. I could have gone with a very expressive yeast to detect changes in flavor. I eventually went with a popular strain that many brewers use for their batches.
3. Every sample will be treated the same and the test batches will be fermented in 1 gallon batches. The original gravity of the beer will be 1.046 and only one hop will be used (see recipe below).

1. Control pitch: 0.75 million cells/ml/º Plato – 32.9 billion cells.
2. Overpitch: 2.5 million cells/ml/º Plato – 112.8 billion cells.
3. Underpitch: 0.1 million cells/ml/º Plato – 4.7 billion cells.

The recipe (4.5 gallon batch to be split into 1 gallon fermentors):

• 7 pounds 2-row Pale malt
• 1 pound of Carapils

Mashed in at 153ºF for one hour. Raised temps to 168ºF for mashout and recirculated as usual. First runnings at 1.063. Second runnings at 1.018. Collected a total of 5.9 gallons at 1.034. Boiled for 60 minutes:

• 0.5 oz of Centennial at 60 minutes.
• 0.5 oz of Centennial at 0 minutes (flameout).
• Whirlfloc and yeast nutrient at 15 minutes.

Cooled to 62ºF and pitched the amount of yeast noted above. I did not oxygenate the wort in any sample. Fermented cool (62ºF) until fermentation slowed then slowly ramped up to 70ºF.

On December 14th the class is scheduled and I will post the results, including flavor and fermentation profiles. I’m also thinking of polling the students to see how each beer scored.

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Results are posted here…

After many months, and finally having the time to come back to the project, I tried again from another commercial bottle of beer. Again I went to a potentially good source of wild yeast and obtained a bottle of Cantillon Blåbaer (2010 vintage). This is a lambic beer and one of their more famous beers. Aged on blueberries from Denmark, Blabåer is a collaboration between a Danish bottle shop, Ølbutikken, and Cantillon. It’s sold only once a year at this shop in Copenhagen and the limit is usually two per person. It is not distributed here in the states and I had the fortunate opportunity to trade for the beer on Beer Advocate.

I opened the bottle almost two months ago, but saved the dregs (about 50 mls) in a sterile conical tube and stored it at 4°C. The first couple of experiments that I did were complete failures:

• 20 μls of lambic slurry into 180 μls of sterile double distlled water (1:10 dilution).
• Made a serial dilution all the way out to 1:1,000,000.
• Plated 50 μls each onto a MYPG, MYPG + bromocresol green, and a WLD plate.
• Incubated at 30°C for two weeks.
• No growth.

I’m sure many homebrewers face this situation, and like professional breweries, planning brewdays based on which kegs / fermenters become empty or based on demand can be challenging. Moreover, homebrewing wisdom dictates that our craft takes time and good beer needs time to condition. On many homebrewing forums I usually see the reccomendation of two weeks or more in primary and two to three more weeks for bottle conditioning an ale.

Many homebrewers think that time is needed to brew good beer and while this may certainly be true, there are exceptions to this rule and one can drink a very good ale in under two weeks. If professional breweries can do it, why can’t we? Critical factors to keep in mind:

Style

Choosing the type of beer is very important. Basically, the lower the ABV the faster the turn around. This means that barleywines and imperial stouts are out of the question. Pale ales, Bitters, and other session ales work perfectly for this. Lagers also may not work since these brews need time to properly ferment (i.e. diacetyl rests) and lager.

Yeast Selection

Selecting the right strain is probably the most important aspect to making a fast beer on the homebrew level. You want to choose a strain that will attenuate fast and have a high floculation rate. A high floculation rate means the beer will clear quicker in the bottle or keg. Unfortunately, higher floculating yeast tend to have lower attenuation rates so plan your brew accordingly. For example, instead of mashing at 154°F, mash at 149°F to maximize fermentability. A favorite strain of mine for this purpose is S-04 or Wyeast 1099 (Whitbred). I have also heard that White labs WLP002 english ale yeast is great choice for fast fermenting beers.

Healthy Fermentation

The expression “time heals all wounds” will not be true here if you don’t have a very healthy fermentation. This means adequate numbers of healthy yeast. Your pitch rate will want to be a bit higher than what Mr. Malty suggests. Prepare your yeast in a big starter or step the starter if needed. If the starter is not on a stir plate, add pure oxygen every once in a while. Prior to pitching the yeast you want to sufficiently aerate your wort. Shaking the carboy will not dissolve the needed oxygen yeast need to grow during the initial lag phase. Use pure oxygen if you can.

Correct Mash Profile

You want to make a wort that the yeast will ferment fast and well. This means using limiting the amount of dextrin type malts (crystal) and mashing low. This will help dry out the beer. If you are brewing extract, use the most fermentable extract you can find such as extra light DME. Make sure to provide plenty of yeast nutrient during the boil.

Force Carbonation

Sorry to homebrewers that enjoy bottle conditioning, but force carbonation of your beer by kegging is crucial to pumping out fast beer. In addition to a floculant yeast strain, adding finings to the keg, such as gelatin will clear the beer even more.

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The recipe below was done in twelve days. The beer took only 3 days to ferment but I racked to a keg on the fourth day. The beer then carbonated for eight days. To carbonate quickly I pressurized my beer at 30 psi on the first day but lowered the pressure 5 psi every day after. The first pint was all yeast but the rest was crystal clear! The only thing I did not follow from above was addition of dextrin malts but I purposefully wanted a less attenuated beer.

Toasted Amber Ale:

• 5 pounds of Maris Otter (Crisp)
• 2 pounds of Mild Malt
• 2 pounds of Munich Malt
• 1 pound of Victory Malt
• 1 pound of Crystal Malt (60L)
• 8.0 oz of Crystal Malt (20L)
• 8.0 oz of Crystal Malt (120L)

Appearance: Pours golden in color and hazy. Big frothy foam for a head that sticks around for a while, undoubtedly due to 50% wheat malt in the beer. Surprisingly not as red as I expected and suggests more hibiscus could be used.

Nose: Soft and delicate malt presence followed by freshly harvested lavender that is not too strong. Some spicy phenols in the background as well which could be from the yeast. The lavender and malt mingle nicely.

Taste: Chamomile is upfront and then gives way floral type of spice. The taste is hard to describe but the beer is not sweet and there is no indication that I added any hibiscus. Bakers dough, wheat, and a slight nuttiness is present. The chamomile is very assertive in the taste. Medium bodied with an agressive carbonation.

Overall: Since this brew was for my wife, Kim, her verdict: “Good. Different, but good”. I have come to appreciate Kim’s palate and I’ll take this as a success. I love the beer and it reminds me of sleepy-time tea with a malty background. The spices are subtle enough that its hard to pick out individual flavors. A few friends of mine were expecting the individual flavors to pop more, especially the hibiscus. Next time around, I might add more spices to the beer and even dry-spice it.

For anyone that is curious, “Chipi” is the nickname for my wife and if anyone can tell me where I got this name from, I will ship you a 24 oz bottle of this beer in addition to some other homebrews. The answer is pretty obscure so I may give hints along the way. Make sure to leave your answers in the commets section and if I’ve already told you the answer in the past, you’re disqualified!

For the flowers I chose hibiscus, lavender, and chamomile. Chamomile is my wife’s favorite ingredient in tea and she loves the smell of lavender. Hibiscus was just something cool I picked up at my local homebrew shop. I hear lavender goes a long way and hibiscus can make a beer blood red. I want all the spices to blend together so I will use a lesser amount of each.

The recipe (5 gallons):

• 6 pounds of German Pilsner malt
• 4 pounds of flaked wheat
• 1 pound of flaked oats
• 4.0 ounces of Carabrown malt (55L)

IBU: ~20

This beer is kegged and ready so I will be posting a review soon.

Happy Brewing!

J

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Tasting Notes: 11/3/11

Part of the reason for lack of posting has been work. My project in Stephen Goff’s lab deals with identifying a human gene that may be required for HIV infection. While my data is potentially exciting, science requires that a hypothesis is proved many times to build confidence in any drawn conclusions. This is what has been keeping me busy.

Also, adjusting to life as a father has been wonderful. Natalie keeps Kim and I busy but she is worth every moment. Some pictures over the three months:

I have much to post about in the coming month:

• Homebrew recipes. While busy, I managed to sneak in a few batches
• Homebrew tastings and reviews.
• The Wild Yeast Project. I’ll post about my latest efforts to isolate wild yeast from Cantillon lambics.
• Yeast Class. On December 14th I’ll be teaching a class on yeast at Brooklyn Homebrew. I’ll post the powerpoint presentation.

I haven’t been able to brew but I was able to keg my quick fermenting 100% Brettanomyces Pale Ale. The idea behind this beer was for me to get some experience in wild ales and fermenting with Brettanomyces. As my Flanders Red Ale is happily souring away, I wanted a quicker fermenting wild ale. The beer was loosely based on the recipe “Sans Le Chat” from Wild Brews by Jeff Sparrow. I added a bit of Vienna and Caravienne malt for more complexity. I made close to 500 billion Brett L and B cells in the lab and the beer fermented down to 1.004 in four days. I kept it in secondary for another month and a half before kegging.

The review:

Appearance: Straw in color with a slight yeast haze. Wheat malt really contributed to the head of the beer as big frothy pillows stick around and leaves considerable lacing.

Smell: Belgian in the nose. Earth, wet hay, and yeast. Tropical aromas reminiscent of pineapple, Bartlett pears, and apples. Malt aromas are completely subdued by the fruity esters produced from the Brett. No noticable funk and hop aroma is non-existent.

Taste: More earthy spiciness from the yeast. Cracked pepper, freshly toasted bread crust and a twinge of sour twang. The sour note is so subtle it might be coming from a fruity ester. Light in body, ample carbonation and bone dry.

Overall: Doesn’t really seem like a wild ale! This beer is more of a cross between a pilsner, a kolsch, and a saison. A very refreshing brew that’s perfect for the last days of summer. As for making a funky wild ale I think this beer falls short. There are two main factors that induce Brett to produce the compounds that are found in funky wild ales – time and oxygen. Time is a factor employed by brews such as lambics, flanders red ales, and american wild ales. When exposed to oxygen, Brettanomyces will produce acetic acid and other souring compounds. This option is problematic since introduction of oxygen post-boil will start beer staling and oxidation. I have bottled at least two six packs of this brew to see if time will change character of the beer.

1. Fluctuating fermentation temperatures (Wyeast 1056; 65°F to 73°F).
2. Significant amount of hop trub in fermentor.