Of yeast and pitch rates

[beersydoesit]

I spent some time over the weekend researching yeast and pitching rates and thought I'd share what I found.

Wyeast Activator smack packs contain a minimum of 100 billion cells plus nutrient, and according to Wyeast, is ready and able to inoculate directly 5 gallons of wort with a specific gravity up to 1.060, at "the pitching rate recommended by professional brewers."

Wyeast also makes a smaller Propogator pack that has 25 billion cells that is designed for making starters.

White Labs offers vials. Their web site states:
"We package each vial with 70 to 140 billion yeast cells, which corresponds approximately to a 1-2 liter size starter."

White Labs' web site states a vial is designed to ferment a 5 gallon batch.
Further they indicate a starter should be used:
"if the gravity is over 1.070, if the yeast is past its "best before" date, or if a faster start is desired."

So both White Labs and Wyeast suggest 100 billion cells or so for OGs of 1.070 and 1.060 respectively

MrMalty indicates that for a 1.060 OG you need 208 billion cells. wtf?

Doing a little quick math, Wyeast's 100 billion cells divided by 18,927 ml in 5 gallons = 5.28 million cells per ml.

Dividing that by 15 degrees plato (60/4 for a 1.060 gravity) yields 352,000 cells/ml/degree Plato.

MrMalty assumes about 750,000 cells/ ml/ degree Plato.
750,000 * 15 degrees plato * 18927 ml = 213 billion cells.

There seems to be a broad consensus that beer should be inoculated with .75 million cells/ ml/degree Plato for ales and 1.5 million cells/ml/degree Plato for lagers.

There is a lot of background here that I don't mean to go into now. However there seems to me to be an assumption that yeast has been harvested and will be repitched as in a commercial brewery.

So, what is going on?

Both Wyeast and White Labs indicate that their yeast is propagated under ideal sterile conditions and is therefore in better shape than what is expected by MrMalty. Further they argue the .75 million to 1.5 million cell/ml/degree Plato values are really pitch rates for repitched yeast as described above.


What to do?

Let us start with the easy ones.

With White Labs OGs over 1.070 should have a starter for sure. ( Except I believe they market some yeasts specifically for high OG beers. Those are outside the scope of this post).

Similarly Wyeast with OGs over 1.060, make a starter.

If your yeast is old, or if you suspect it has had a rough shipment, make a starter.

As to the rest, I don't know. I'm inclined to trust White Labs and Wyeast, and I seem to get fresh yeast at my LHBS but I haven't been brewing that long.

I've seen some suggest that while a starter may not necessarily be needed below 1.060, they get more consistently good results by using a starter.

I haven't been brewing long enough to argue with that.

I've brewed big beers (OG 1.080) with one Activator with tasty results. The yeast was fresh, and perhaps I got lucky. I wouldn't bet on that working again.

But for OG 1.060 with fresh White Labs or Wyeast I might.

I've also pitched two Activator packs in one batch. Kinda pricey.

Making a starter isn't hard but there are downsides

1) You have to start it days ahead.
2) For a noob, everything can be a little overwhelming so if a starter isn't strictly necessary it might not be worth it. (Or it might be better to spend a little more and pitch two Activators or Vials)
3) It approximately doubles your risk of infection. Essentially you brew two beers, (one small) and each carries a risk of infection. If your sanitizing practice is good this risk remains small but non-zero.


MrMalty has a pitch rate calculator here
Mr Malty Pitching Rate Calculator

I like Wyeast's better here
Wyeast Laboratories : Home Enthusiasts : Brewers : Pitch Rate Calculator

because it tells me how many cells/ml I am getting. Even if I accept the higher pitching requirements this calculator is nice. It also has nice starter making instructions.

That is liquid yeast, what about dry?
Danstar's Nottingham yeast has about 5 billion cells per gram and comes in 11 gram packets. That is 55 billion cells per packet.
So two packets would compare in cell count to an Activator pack.

Indeed from Danstar's website the rehydration and usage tips seems to suggest 1g/L, or 20 grams in 5 gallons.
Danstar Premium Beer Yeasts - The Dry Yeast Advantage

I haven't used dry yeast so I don't know how many packets people use.

I've found no evidence that anyone feels there is a risk of a homebrewer over pitching yeast.

A good weekend for me.:rockin:

 

[nakros]

Great research! Thanks very much for sharing. Very interesting information.

Out of interest sakes (I've wondered it myself, after reading how many yeast get pitched), do you have any idea how many yeast (give or take a few billion) it takes to ferment a 5 gal batch, after they have reproduced and such? Or are the numbers above pretty close to it?

Thanks again for sharing your research!

 

[Rhymenoceros]

Thanks for the research. I would like to see some of the pro's chime in on this because the whole starter business is a tad confusing with all of the contradictory information out there. What I do know is that in the 3 beers I've brewed I have just pitched the yeast straight from the container (one dry, and 2 white labs vials) and have gotten active fermentation with in 18 hours each time. However, I can't attest to the taste of the latter 2 because they are still fermenting.

 

[llazy_llama]

Wow, very nice post. All of my batches save one have been using White Labs liquid yeast that I pitched without starter. This post really made me stop and think though. I think from now on when/if I pitch dry yeast, I'll have to either use a starter or pitch two packs.

Thanks for the info. I found it very helpful.

 

[944play]

So two packets would compare in cell count to an Activator pack.

Everything I have read indicates that there are MORE cells in a packet of dry yeast, including JZ who estimates 20 billion cells/gm.

 

[beersydoesit]

Could be. I went to Danstar for my info.
www.danstaryeast.com/nottingham.HTML

20billion per gram * 11 grams yields 220 billion cells.

 

[TwoHeart]

Sorry to bring up an old thread. But I was under the impression that once the yeast started going that it would reproduce and eat all of the fermentable sugars, no matter what the OG.

If you are only using a small amount of wort to produce a starter, what is the difference in using a full 5 gallon of wort?

 

[pfgonzo]

Quick note: Chris White, in his Yeast book, talks about proper pitching rates, and it varies whether you're using a previous batch of harvested yeast, or a lab-pure culture. I don't have a page cite, but he says you can use up to 50% of the amount if you're using a lab-pure culture... like a vial of WL yeast, or a Wyeast smack pack. In other words, one pack is sufficient for a 5ga batch of 1.060 wort.

 

[jeffjm]

Sorry to bring up an old thread. But I was under the impression that once the yeast started going that it would reproduce and eat all of the fermentable sugars, no matter what the OG.

If you are only using a small amount of wort to produce a starter, what is the difference in using a full 5 gallon of wort?

There's only so many times any individual yeast cell can reproduce. If you hit that limit before you get to your intended final gravity, you've stressed the yeast, causing off-flavors at a minimum, and possibly causing your beer to under-attenuate. Limits on cell reproduction are determined by available oxygen, available nutrients, and probably a few other things I'd be able to remember if I hadn't just had a few pints

The bigger the starter, the more yeast cells you grow, which reduces the number of times any individual cell has to reproduce before the fermentable sugars in your main batch run out. Even if you make a starter with zero cell growth, you've woken up your yeast and gotten them used to fermenting sugars, as opposed to pitching them cold and sluggish straight from the fridge.

 

[Malticulous]

There are styles of ales that the 5-6 billion/ml pitch rates work well with. It has a big effect on getting the proper esters. There are many brewing books that recommend as little as twice that for lagers. The truth is pitch rates are very strain and style specific. If the beer is how you wanted it you pitched the proper amount.

I've been making my starters out of my wort lately. I can only get my wort to 80F. I take the starter and cool in in an ice bath as the rest of wort in the fermenter cools in my fridge. When the starter starts to gas off co2 I pitch it into the cooled wort. It only takes 2-4 hours.

When I get a new yeast I start with a lower gravity beer so I don't need much of a starter and I'll have more healthy yeast to repitch. With the cake I can make 2-4 more batches (700-800 billion cells.) I've repitched for over 10 batches before (never washing) with good results. Lower pitch rates can also lead to a more healthy culture because you will have more daughter cells.

 

[OohLaLa]

bumping this to keep it going. Good information on differences in pitch rates between reused yeast and factory fresh yeast. Did a lot of research on this myself when I moved to yeast washing. Summarized nicely here.