Pitching Rate Theology

yeastprep
Yeast rehydrating in 660 grams of water – 10X the dry weight of the yeast to pitch

Trying to find consistent and credible information on yeast pitching rates is a bit like theology. Trying to find out how many yeast cells are in a pouch of yeast is like trying to find out how many angels can dance on the head of a pin! A lot of people agree, but when they disagree, it’s passionate and usually by a long margin. I would really love to understand precisely how much yeast to pitch, how to manage to keep it healthy and happy, and ultimately make wonderful beer.

First, dry versus liquid yeasts… I always select the yeast that is appropriate for a given style and then move to convenience. Frankly I do not care to make starters unless absolutely necessary – and it is usually absolutely necessary for me when I use liquid yeast. At $7.00 a vial or smack pack, I am not all that interested in investing $21-28 bucks just for a viable healthy pitch of convenience. So then I am required to make a starter and this must work back from my planned brew day – say start 4 days ahead and pray I can reserve the dedicated time to brew. I am a huge fan of dry yeast and its convenience, however, the limitations of strains are a problem. Liquid or dry – yeast pitches should be the same, assuming good health and viability.

For the anti-starter types and the pitchers of dry yeast into wort, I have found that starters and/or hydration to produce the best and consistent fermentation in my brewing. If an easier path works for you – awesome. No point in reading further!

For convenience sake, homebrew supply stores have reduced pitching yeast to a common denominator, generally 1 sachet of dry yeast for 5 gallons of normal gravity beer, double for higher. Same with liquid yeast. This results in wildly differing pitch rates, and a potential source for homebrewer mythology. One can simply read the thousands of “my beer is stuck” posts on Homebrewtalk.com and see that 1 package or vial of yeast in 1.110 wort is going to be troublesome…

I do contend that regardless of packaging or medium (liquid versus dry) we should attempt to pitch the CORRECT amount of yeast to see consistent and reliable results.

Sean Terrill’s blog has some interesting experiment results, and his findings of 8 – 18 million cells per gram support MrMalty.com’s assertion that there are approximately 20 billion cells per gram of dry yeast, so in a 11.5 gram sachet, there should be approximately 230 billion cells, however Lallemand claims only 6 billion cells per gram, resulting in 69 billion cells per sachet, and in fact there are tables floating around the internet of WIDELY varying cell density. That is a HUGE discrepancy, and I use the manufacturer’s numbers personally – and maybe over pitching. In a White Labs vial or a Wyeast Smack Pack, there are approximately 100 billion cells. Good general working numbers.

Viability needs to be understood, meaning that yeast will die off in the packaging, reducing the overall viable cells, over time. These are variable based on time, temperature and handling. As such, check the dates, and use a calculator to determine the remain number of potential viable cells. I should add that packaging may dictate the use of weight in grams (dry) or volume in milliliters (liquid, slurry). Simply – you want the freshest yeast possible. Here dry again wins me over – being SLIGHTLY more stable, and certainly longer lived. It is always in stock in my fridge.

We need to determine the correct amount to pitch in relationship to the specific gravity of our wort. First determine gravity – and then wort volume as the math becomes easier. Then go back to our manufacturer source and determine the pitching density of our package.

(pitching yeast density in millions/ml) X (milliliters of wort) X (degrees Plato of the wort) = total pitch yeast cells

In the book “Yeast” (great book btw) – Chris White and Jamil Zainasheff propose that 1 million cells per ml is the generally accepted pitching rate, but that .75 million cells for ale and 1.5 million cells for lagers is more appropriate (per milliliter). I see no delineation between profession or homebrewer scaled pitching in their recommendations. We are dealing with yeast and they don’t know the skill level of the brewer.  Master brewers will adjust pitching rates to push the yeast to produce a specific flavor or attenuate higher or lower, as another tool in their bag of tricks.

If you look at Brewer’s Friend’s Yeast Pitch Rate and Starter calculator, there is a drop down for “Pro” settings that range from 0.75 to 1.25 million cells/ml for ales and steps up for lagers starting at 1.5 up to 2.0 million cells / ml. Above that are significantly lower manufacturer recommendations at .35 and .5 million cells/ml respectively. I find it fascinating that there is such a very wide range of recommendations, and seems to confirm that brewers pitch at dramatically different rates, and a convenience for homebrewers looking for a quick setting for their special beer.

Into the math for my recent “Houston We Have a Pale Ale Part Deux”  where the gravity was 1.061 into the fermenter. This equates to 14.66 degrees Plato. I am going to pick a 1.0 million cells/ml Pro pitching rate in Brewer’s Friend Yeast Calc. since I am past the 1.050 gravity line. We have an 11 gallon batch which equals 41639.8 ml of wort.

(yeast density in millions/ml) X (milliliters of wort) X (degrees Plato of the wort)= Required cells to pitch

(1,000,000 million/ml cells) X (41639.8 ml wort) X (14.66 degrees Plato) = 610,439,468,000 required cells, or round to ~610 billion cells

I used Danstar’s BRY-97 West Coast Ale, which documents about 5 billion cells per gram in a 11 gram package. This would equal 55 billion cells per sachet. This is a lot lower than the assumed 20 billion cells per gram by MrMalty.com.

610 billion cells required = 122 grams of BRY-97, roughly 11 sachets. Now, weigh that out carefully, and following instructions, rehydrate in 1220 grams of warm sterile water and let sit. After 15 minutes stir gently – adjust temperature to wort temp and pitch. In my case, I built a 2-step stir plate starter to achieve the adequate cell count.

My conclusion to this is the following:

  1. Consistency and repeat ability are likely MORE important than which variable on yeast density you choose. Pick one and use it consistently. I cannot tell you which is best, but if you use a reference and stick to it – then you have that baseline to adjust and troubleshoot when there is a problem.
  2. This is horse shoes and hand grenades – a few million yeast cells either way are not going to make a tremendous difference. However when you scale your batches up – those errors are amplified. For most of us – it shouldn’t be a worry.
  3. Setting a baseline will help to establish the proper yeast character for a given style, and adjustments can tweak toward the desired property. Example – common practice is to under pitch a belgian yeast to stress it – and produce more “belgian” character – as well as manipulate the temperature for esters or phenolics.
  4. Gravity definitely comes into play, don’t base your pitching rate only on how much beer is in the fermenter!
  5. Don’t cheap out. I am cheap – but especially when using dry yeast, it’s so inexpensive to use 3 sachets, rather than a single. However, when using liquid yeast, starters are ALWAYS insurance on getting the right pitch counts and making sure it survived in the hot car on the way home! And don’t be too afraid to make a starter with dry, just make sure to oxygenate your wort when pitching.
  6. Clean and sanitize! I didn’t cover this above, but for your beer’s sake and the yeast’s sake – make sure everything that touches the wort AND the yeast handling process is clean and sanitary, INCLUDING the package. If in doubt, stop and sanitize – that bottle of StarSan is your friend!

Now… how many yeast cells can dance on the head of a pin? I guess it depends if you believe the manufacturer or MrMalty? Now let’s hope my math skills aren’t so rusty that I made a huge mistake!

 

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