Pitch the right amount of yeast or pitch your beer!
I truly believe that incorrect pitch rate is the fatal flaw of homebrewing. Hell, even some brewpubs suffer from this mistake. Proper and complete sanitation is my motto, but even if you keep everything squeaky clean, infections are most definitely not the biggest cause of mediocre beer. I once knew a guy who told me “just make good clean beer first, then you can do whatever you want to it”. He was talking about making the fermentation as “clean” as possible. Even if your equipment was dirty, if you put the right amount of yeast in there those little warriors can fight off most infections. Yeast produces alcohol, which is the enemy of bacteria.
Brewers’ Yeast-Lagers and Ales
To begin, I want to cover a few very broad points about yeast, discuss liquid vs. dry, and just briefly cover flavor components before we get a little more technical. First, there are two broad categories that brewers separate yeast into: Lager and Ale. Lagers taste better fermented cold (around 50F) and Ales taste better fermented at or around room temperature(70F). As far as yeast goes that’s narrow enough for today’s discussion (if you want to know about bacterias and wild yeast strains ask the O’Connor’s staff). For the purpose of this article, I want to focus on the previously mentioned Lager and Ale Yeasts.
The Two Phases of Yeast
Yeast has two general phases: 1) Aerobic – During this phase the yeast uses oxygen to produce cells (reproduce). 2) Anaerobic – During this phase we see the yeast using glucose to create CO2 and Ethanol (Fermentation). When you are pitching yeast into your beer obviously you want the second phase to be in full swing, and that is the main reason for not over oxygenating your wort. Fortunately as a homebrewer you would really need to shake your fermenter for a whole week or dump a tank of oxygen into it to force constant aerobic activity.
Liquid vs. Dry Yeast. What’s right for your beer?
The difference between the two is very similar to the difference between liquid malt and dry malt extract. Dry yeast is just processed one step further to make it more storable. Both are obviously good for fermentation. One of the most important factors when using either dry or liquid is using them consistently in order to get repeatable results. I think of dry yeast as the boring less attractive friend of liquid yeast. It is consistent and it will always be there for you, but it is definitely more fun to go party with the younger and more interesting liquid stuff. The biggest problem with the liquid is that it is much more needy and it spoils MUCH quicker. Lucky for you we handle the spoilage by never selling yeast that is “out of date”. Hard as it is to pull a product without selling it, we do that here because yeast is alive and we do not want you to be making bad beer with dead yeast. Different yeasts make different beers, and the liquid has much more variance in selection. Regardless of what type you are using, you want to get consistent results, and that means you need to do something about that pitching rate!
Here Comes the Technical Part
Pitching rates are dictated by your original gravity and the volume of your beer. Professional brewers measure this by mL per degree Plato. For the sake of this article I will try to convert all of my numbers into the homebrewer friendly “gravity” points. This is how I get that gravity number: multiply ºPlato by 4 and get the number you’re familiar with (4P = 1.016; 12P = 1.048). If you want to get the exact conversion you can use the charts here: http://www.brewersfriend.com/plato-to-sg-conversion-chart/ .
Dry yeast packages contain around 230 billion cells and Wyeast packages hold about 100 billion. The formula for proper pitching rate for Ales is:
(1 million cells x mL of wort) x º Plato
If you’re starting with a 1.048 starting gravity you need to first convert gallons to mL and SG to ºP.
1.048 is 12ºP and 5 Gallons is 18927.2 mL
(1,000,000 x 18927.2) x 12 = 227,126,400,000
For lagers you would ideally take this number and triple it-so just under 700 billion cells.
227 billion cells!!! BILLION. Do not be afraid of the big numbers. Now is the part where you say, “Wait, what the WHAT!? My Wyeast package says its good for a 1.060 SG and now you’re telling me I need almost 3 times that for 12 gravity points lower?” Yep, but here is the dirty little secret about yeast pitching: when you introduce yeast to the wort party the freshness of yeast (called viability by the pros) causes reliable results with up to 40% of recommended rates. Don’t ask me why that is the case, because that is microbiology, and I am just spouting that information from a micro PhD student that I happen to know. Viability of your yeast needs to be a concern whenever brewing but in particular when you are using less than the recommended rates. If your yeast is not fresh then you had better be doing a starter regardless of your starting gravity. If you are doing anything with liquid yeast, it is always going to benefit from a starter… and for that matter using dry yeast and doing a starter is not bad either. Dry yeast companies do not recommend using their yeast for starters, because it is not economical (dry yeast tends to be inexpensive and buying another pack costs less than the time and effort spent to make a starter, but I know homebrewers and I know you want to save that 50¢).
How to Make a Yeast Starter
Doing a starter is making a miniature batch of beer ahead of time. You can add that beer directly to be batch you make, or you can put the yeast starter in the fridge and decant the beer at a later time. Whichever route you choose, it is never going to hurt your beer. It is always going to improve it and we have some pretty simple instructions to do it here: http://crashtest.emberlydigital.com/2012/09/how-to-make-a-yeast-starter/. This is one of the best tried and true websites for figuring out how much yeast you need: http://www.mrmalty.com/calc/calc.html
If this article just made you hungry for more you can slake your unquenchable thirst for knowledge by reading Yeast by Jamil Zainasheff and Chris White -available for your purchasing pleasure at O’Connor’s.
Until next time, Sanitize Sanitize Sanitize (and pitch the right amount of yeast).
O’Connor’s HBS’s General Manager and Home Brew Expert