Yeast Pitching Rates

[donniestyle]

Several individuals and I have disagreed on this topic in the recent past. I am posting my calculations for public consumption.

First, some basic conversions.
1 L = 33.8 oz
5 gal = 640 oz
640 oz / 33.8 oz/L = 18.935 L
5 gal = 18.935 L
1 gal = 3.787 L
3.787 L = 3787 ml

Optimum pitch rates: see Wyeast site for more information. Rates quoted are 6, 12, and >18 million yeast cells per milliliter of wort. The rates quoted are for pitching yeast from a previous fermentation. They are also for pitching at temperatures greater than some home brewers practice. Thus, pitching rates may need to be even greater in certain circumstances.

Here are my calculations.
AMOUNT OF PITCHABLE CELLS NEEDED FOR 5 GALLONS OF WORT
6,000,000 * 18.935 L * 1000 ml/L = 18935 ml * 6,000,000 = 113,610,000,000 cells
12,000,000 * 18.935 L * 1000 ml/L = 18935 ml * 12,000,000 = 227,220,000,000 cells
18,000,000 * 18.935 L * 1000 ml/L = 18935 ml * 18,000,000 = 340,830,000,000 cells
24,000,000 * 18.935 L * 1000 ml/L = 18935 ml * 24,000,000 = 454,440,000,000 cells

Now, look at the contents of different yeast packaging.
Wyeast propagator has 25,000,000,000 yeast cells
Wyeast activator has 100,000,000,000 yeast cells
White labs pitchable has 75,000,000,000 to 150,000,000,000 yeast cells
Dry yeast has about 5-6 billion cells per gram.

Take the W34/70 dry lager yeast, at 6 * 10^9 cells per gram, in a 11.5 gram package.
6 * 10^9 * 11.5 = 69,000,000,000 cells (69 Billion)

Thus, if I were to need > 18,000,000 cells per milliliter, I would need to pitch about the following.
340,830,000,000 / 69,000,000,000 = 4.9395652173913043478260869565217 packages.


Yeast propagation is another subject, and Wyeast also provides a pitch rate calculator on their site. Check it out when you plan to make your next starter. Here's a sample; the "yields" number comes from the Wyeast pitch rate calculator, pitching 1 Wyeast Activator into the starter size specified. The batch size is 5 gallons. For batch sizes other than 5 gallons, scale the "yields" and "total yeast cells" numbers accordingly.

ONE STEP STARTER NO STIR PLATE
0.25 gal pitch yields 9.09 million cells/ml = 9,090,000 cells/ml * 18,935 ml = 172,119,150,000 total yeast cells
0.30 gal pitch yields 9.74 million cells/ml = 9,740,000 cells/ml * 18,935 ml = 184,426,900,000 total yeast cells
0.35 gal pitch yields 10.31 million cells/ml = 10,310,000 cells/ml * 18,935 ml = 195,219,850,000 total yeast cells
0.40 gal pitch yields 10.83 million cells/ml = 10,830,000 cells/ml * 18,935 ml = 205,066,050,000 total yeast cells
0.45 gal pitch yields 11.29 million cells/ml = 11,290,000 cells/ml * 18,935 ml = 213,776,150,000 total yeast cells
0.50 gal pitch yields 11.71 million cells/ml = 11,710,000 cells/ml * 18,935 ml = 221,728,850,000 total yeast cells
0.55 gal pitch yields 12.09 million cells/ml = 12,090,000 cells/ml * 18,935 ml = 228,924,150,000 total yeast cells
0.60 gal pitch yields 12.44 million cells/ml = 12,440,000 cells/ml * 18,935 ml = 235,551,400,000 total yeast cells
0.65 gal pitch yields 12.77 million cells/ml = 12,770,000 cells/ml * 18,935 ml = 241,799,950,000 total yeast cells
0.70 gal pitch yields 13.07 million cells/ml = 13,070,000 cells/ml * 18,935 ml = 247,480,450,000 total yeast cells
0.75 gal pitch yields 13.35 million cells/ml = 13,350,000 cells/ml * 18,935 ml = 252,782,250,000 total yeast cells

ONE STEP STARTER ON STIR PLATE
0.25 gal pitch yields 12.72 million cells/ml = 12,720,000 cells/ml * 18,935 ml = 240,853,200,000 total yeast cells
0.30 gal pitch yields 13.64 million cells/ml = 13,640,000 cells/ml * 18,935 ml = 258,273,400,000 total yeast cells
0.35 gal pitch yields 14.44 million cells/ml = 14,440,000 cells/ml * 18,935 ml = 273,421,400,000 total yeast cells
0.40 gal pitch yields 15.16 million cells/ml = 15,160,000 cells/ml * 18,935 ml = 287,054,600,000 total yeast cells
0.45 gal pitch yields 15.80 million cells/ml = 15,800,000 cells/ml * 18,935 ml = 299,173,000,000 total yeast cells
0.50 gal pitch yields 16.39 million cells/ml = 16,390,000 cells/ml * 18,935 ml = 310,344,650,000 total yeast cells
0.55 gal pitch yields 16.93 million cells/ml = 16,930,000 cells/ml * 18,935 ml = 320,569,550,000 total yeast cells
0.60 gal pitch yields 17.42 million cells/ml = 17,420,000 cells/ml * 18,935 ml = 329,847,700,000 total yeast cells
0.65 gal pitch yields 17.87 million cells/ml = 17,870,000 cells/ml * 18,935 ml = 338,368,450,000 total yeast cells
0.70 gal pitch yields 18.29 million cells/ml = 18,290,000 cells/ml * 18,935 ml = 346,321,150,000 total yeast cells
0.75 gal pitch yields 18.69 million cells/ml = 18,690,000 cells/ml * 18,935 ml = 353,895,150,000 total yeast cells

Conclusion: Most home brewers under pitch.

[Brewboy]

Good numbers there Donnie. Pitching for lagers does need to be double the cell counts pitched for ales.

Also, sometimes underpitching can yield the esters we're looking for in an ale.

Higher pitching rates creates cleaner fermentations with less esters produced and lower finished gravities.

So, if my target is a very clean fermentation and a dry ale, (kolsch, cream ale, blone ale......) I'd pitch high. If brewing a Hefeweisen, or english bitter, I prefer underpitching a bit to bring out the esters I'm looking for.

Big beers are another story alltogether. You need huge starters to consume all the sugars these worts cary.

[Jimmy Orkin]

Jamil Zainasheff also has a pitching rate calculator. It is at this link:

http://www.mrmalty.com/calc/calc.html

Leroy and I are making a Baltic Porter at the brewday. It is a lager with OG 1.089 and 5 gallons.
Jamil says we need 604,000,000,000 cells to pitch.

[donniestyle]

I think 604B is probably a good number. Note the pitch temperature is important. Too cold, and the yeast growth will be much less (<65). That's yet another reason to get lager pitch rates higher - to avoid the high temperature growth phase - leading to esters.

I've yet to do more research on over pitching problems, but I have seen they are much less severe than under pitching, and it really takes a lot of yeast. I decided that I cannot culture enough to over pitch. I used 6 packages of T58 in a 1.085 triple, and the fermentation temperature was 78F. It had a little banana initially, but it's all gone now.

[Brewboy]

The dicussion with Dennis at the meeting last nigh has me thinking hard about yeast starters.

When should a starter be pitched?

I've read and heard many as does Dennis that claim high krausen is the time to pitch. I've pitched at this stage because of what others have claimed but very simply it just doesn't make sence to me.

Let me explain:
There are several stages to yeast life cycle and according to Dr. MB Raines they are:

http://www.maltosefalcons.com/tech/MB_R ... turing.php

"Initially there is a lag phase. This occurs during the first few hours after addition of the yeast. During this time there are no apparent signs of fermentation or growth. The yeast are becoming acclimated to their new environment. If the previous media (or starter) is similar to this new one, acclimation will occur rapidly and the lag phase will be short. If there are major differences in the gravity, temperature, or wort composition, the yeast may be surprised or shocked and it may take some time to adjust to this new environment. Major changes occur within the yeast at this time, they are absorbing all of the oxygen in the wort, using it to synthesize all the enzymes and other metabolic machinery necessary for growth and fermentation, and storing oxygen up in the form of sterols for later use. This stage is critical to fermentation and should occur as rapidly as possible, preferably within a few hours.

II) The second phase is the accelerating growth phase during which yeast cells start to grow and divide. Signs of fermentation will also become apparent. The yeast begin storing sugar in the form of glycogen for later use.

III) The third phase is the exponential phase where yeast reproduction and metabolism is in high gear. Cells are dividing every 90 - 180 minutes and fermentation begins. During this time the number of yeast cells may increase as much as 1000-fold (or 3.0 logs) within 24 hours. The extent to which the cells divide is dictated primarily by the pitching rate. If appropriate pitching rates are used, the yeast are pitched at high concentrations (5-15 million yeast cells per ml) and undergo approximately 3 generations (23- or an 8-fold increase in cell number) to yield 80-100 million cells per ml. 100 million cells per ml is about the maximal concentration of yeast attainable in fermenting wort (Figure 2 &mp; 3). Fermentation is also very active and a krausen may be beginning to form.

IV) The fourth phase is the decelerating growth which should occur 12-24 hours after pitching. At this time the oxygen is fully depleted and fermentation and CO2 production is taking over. Fermenting wort should be in high krausen. Maximal fermentation occurs during 12-48 hours; heat is being generated and there should be rapid CO2 evolution (bubbling).

V) Finally several days later, the yeast enter astationary phase. During this time the fermentables and nutrients are completely consumed. All yeast growth has stopped and they are beginning to fall out of suspension or flocculate. "

The purpose of a yeast starter is to pitch a higher cell count into your wort. We do this to create less stress on the yeast cells in the propogation phase keeping the growth to 3 generations or less.

So unless we're pitching a full maximum concentration of yeast cells (100 million cells per ml), the yeast still have to go through all the phases of it's life cycle to reach adequate concentration levels.

When we pitch at high krausen (4th phase of yeast life cycle) aren't we actually forcing the yeast to either consume the available fermentable at whatever rate we pitched or forcing the yeast to shift gears and go back into a lag phase? Most likely the latter. The new oxygen rich enviornment should put them back into the lag cycle and propogation phases.

During the astationary phase (the process through which yeast flocculates and settles to the bottom of the fermenter following fermentation) the yeast begins to undergo a process that will preserve its life as it readies itself for dormancy, by producing a substance called glycogen. Glycogen is necessary for cell maintenance during dormancy and is an energy source during the lag phase of fermentation.

So if we pitch the yeast before the astationary phase, we shortcut the glycogen production and stores that help the yeast make it through the next 3 generations of propogation we're asking it to do.

I know that this is a lot of info. I conclude from this data that a yeast starter is in better shape for pitching after the astationary phase.

If any of you have data to the contrary, I'd love to see it.

[donniestyle]

Thanks for the link to Dr Raines page. I haven't seen that before. I'm going to assimilate it. You should also check out the BJCP study guide at http://www.bjcp.org/study.php#yeast, and the other links we have on our site under the heading Yeast at http://www.nthba.org/content/brewers-library. According to the BJCP study guide, the phases are: Lag phase, Growth phase, Low kraeusen, High krausen, and Late krausen. Check out these sources also.

[BrotherhoodBrew]

Some other yeast starter info ( audio format )
http://thebrewingnetwork.com/shows/Brew ... t-Starters
http://thebrewingnetwork.com/shows/470
http://thebrewingnetwork.com/shows/The- ... s-Yeast-Co
http://thebrewingnetwork.com/shows/The- ... -White-s-2
http://thebrewingnetwork.com/shows/The- ... ve-Logsdon
http://thebrewingnetwork.com/shows/The- ... White-Labs
http://thebrewingnetwork.com/shows/The- ... rmentation
http://thebrewingnetwork.com/shows/The- ... rmentation

I personally will only pitch active starters in certain situations. I do not want to pitch a bunch of starter wort into most of my beers.

[donniestyle]

Update to Dr Raines information. Figure 1 quotes Ray Daniels from HBD 1746, on May 31, 1995, where Ray says the following:
"A bloated pack of Wyeast contains 1 to 5 billion yeast cells. If you pitch one
pack into a 1.040 O.G. one quart starter, you will wind up with about 20 billion
cells in the starter (Again, I've counted.) We all know you can pitch the
quarter starter and have a decent ferment, but it is way short of the yeast
count you can deliver with just ONE packet of (fresh, properly stored) dry
yeast. (Also way short of commercially recommended pitching rate of about 200
billion cells."

The current WYeast Propagator has 25 billion yeast cells, and the Activator has 100 billion.

Looking back at that HBD issue suggests to me that we severely under pitched back then. Thus our beers would have had much higher levels of off flavors, unless we were making starters. I remember making 2 and 3 step starters back then.

I'm not near through reading it, but I haven't seen any mention that wort temperature (colder) and the presence of glucose will also inhibit yeast growth. If the wort contains more than 0.4% glucose, yeast will skip the growth phase; this is known as the Crabtree effect. I've got to refresh myself on the temperature specifics. It's either that the wort does not absorb as much oxygen, the yeast process less, or both. This also leads to less yeast growth.

[Brewboy]

Good point about the crabtree effect and this is exactly why on big beers that contain some sugar in them, you must hold it back until later in the fermentation to add it. Only after the yeast have consumed the maltose do you allow them to move on to the glucose.

[donniestyle]

Overall the Raines article was great. I don't get nearly that detailed in my yeast propagation - relax, don't worry, have a home brew. I control my starter temperature. I grow Belgian starters at 75-80, ale starters at 65-70, and lager starters at 60. Most of the time, they are on a stir plate. They are at least 1000-1500 ml starters, and sometimes 2000. I start with a Wyeast Activator, or a White Labs vial. I prefer to decant most of the liquid.

Lets say I do a lager starter with 2000 ml and 1 Wyeast Activator. According to their pitch rate calculator, I will have 16.7 million cells per milliliter when the starter is pitched into 5 gallons of wort. This is sufficient for worts under 1.060.

It is not noted, but I assume the Wyeast pitch rate calculator is based on propagation temperature of 75F, since that is the temperature they recommend growing starters at. Thus, yeast growth would be less at lower temperatures. It would be awsome if the pitch rate calculator has a temperature input.

[Captain Kangabrew]

I do mainly 2000 ml starters, for both lagers and ales. Some say you should do twice as much for lagers, but I feel comfortable with my methods. I have been using a stir plate for the last year or so with great success. I built my own for about $15 using this link: http://onebeer.net/sp_howto.shtml

I also find that repitching yeast is the best method. I steralize mason jars in my pressure cooker, allow to cool and pour what's left in my carboy into 3 or 4 for later batches. If the yeast sits around for a while sometimes my fermentation doesn't get started as quickly as I'd like, but always within 12 to 24 hours. Have not had any contamination problems so far.

The above information is great, as long as you like to read. The Brewing Network links are also very informative. Some of the best information I received when I was new to harvesting yeast was from http://www.basicbrewingradio.com If you go to the podcasts dated 10/27/05, 11/3/05 and 11/10/05, Dave Logsdon of Wyeast talks for days about yeast. Some great information in about three hours of audio. While I am a big supporter of http://www.thebrewingnetwork.com , sometimes my time is just too valuable to listen to a 3 or 4 hour show, even for great information.

[RobDrechsler]

...I have been using a stir plate for the last year or so with great success. I built my own for about $15 using this link: http://onebeer.net/sp_howto.shtml

Nice link to the diy stir plate... one thing the article leaves out , what do you use as the stirrer? a chunk of iron?

[RobDrechsler]

Erik from the article answered my question...


Magnetic Stir Bar doh!