Yeast Starter

How-to: Planning a Yeast Starter

Recently I’ve been working with yeast starters to improve my beer. Having done a few now, I wish I had started doing these earlier. Yeast starters are one of the most cost-effective (and fun!) ways to improve the quality of your beer. If you like brewing high gravity ales, lagers of any gravity, or simply have an old yeast pack/vial sitting around and you want to get the most out of it, read on.

In this article you’ll learn how to calculate just how much yeast you need to pitch, and how to get to that amount using one or more sequential yeast starters. In Yeast Starters II you’ll learn how to take our calculations derived here and turn them into real beer-making, flavor-popping, blowoff-clogging yeast.

Planning a Yeast Starter: At a glance

For starters…

When I first started brewing I was happy to just pitch a smack pack of Wyeast, or a vial of White Labs into my wort and not think anything more about it. After all, most of what I read was that liquid yeast gave much better results than dry yeast packets (at least this was the case back then). While Wyeast and White Labs make an excellent product, there is a reasonably simple, cost-effective way to make their products even more suitable for use in your homebrew.

Why use a yeast starter? Simply put, in most cases yeast starters will reduce off-flavors in your beer, decrease the risk of contamination, and ensure a robust fermentation that will provide optimal conversion of sugars to carbon dioxide and alcohol.

Better Yeast = Better Beer

Fortunately making a yeast starter is really easy. Like most things in home brewing, you can do this very cheaply with stuff you probably have around your house. A few small investments can really help if you want to optimize the process. But before we talk about equipment, let’s walk you through the process of planning a yeast starter.

Step 1: Determining Your Pitch Rate

Before you begin, you need to decide how much you actually need to pitch in order to ferment your beer without too much stress on the yeast. I recommend using a Yeast Pitching Rate Calculator. I personally use the calculator available at Brewer’s Friend, though many people have also recommended the calculator at Mr. Malty. Many home brewing software packages also contain a similar calculator. One nice feature about the Brewer’s Friend calculator is that you first calculate how many yeast cells you actually need to pitch, and then you can plan steps to generate that much yeast from your existing supply.

OK… as an example let’s assume we are going to brew 5.5 gallons of Oktoberfest (lager) with an OG of 1.058. All we have on hand is a single smack pack of 90-day-old Wyeast Oktoberfest 2633. Here is the recommended pitch rate from our calculator:

An example suggested pitch rate for a lager with an OG of 1.058.

According to our calculator, we have about 37 billion yeast cells available (from our old smack pack), but we need to pitch about 520 billion cells! We DEFINITELY need to make a yeast starter.

Step 2: Determining Your Starter Size

The next part of the calculator allows us to grab our starting number of cells (i.e. the “Cells Available” from the first part) and see how many cells we can create with a starter. In general, when starting with a vial or smack pack, making a 1 to 2 liter starter is an ideal size. Let’s start with a 1L starter:

1L Starter - No agitation

You can see from our first step that with 1L of water and 100gm of DME, we can grow our yeast to 88 billion cells. Not too shabby.

A closer look…

Let’s look closer at our options to see if we can improve this yield. If we look at the “Growth Model and Aeration” section, we see several options. In our original example we selected “No Agitation,” but we could also select “Shaking” and two different calculation options for “Stirplate.” Each of these options corresponds to how much we move or agitate the yeast while it’s doing its job in the starter. Let’s see how changing the agitation of the wort changes our yield:

While no agitation gets us 88 billion cells, periodically shaking the starter gets us 107 billion cells. That’s almost 20 billion more cells just by walking over to the starter every time we think of it and giving it a good swirl. If we invest in a stir plate, we can increase our yield to 181 billion cells!

A stir plate, while not absolutely necessary, can be a great investment if you plan on doing yeast starters for your beer. If you’re on the fence about getting one, run a few of your favorite recipes through this calculator and see how much it will help you. Stir plates are available from any homebrew retailer (NB, B3), specialty online stores like StirStarters, or you can make your own!

Back to our starter…

Let’s assume that we don’t have a stir plate, but we are willing to agitate (shake or swirl) the solution every time we walk by (we, as home brewers should be able to make such sacrifices). We can make 107 billion yeast cells with our 1L starter. That seems pretty good, but what happens if we increase our starter size to 1.5L? How about 2L? Let’s see:

While a 1L starter gets us 107 billion cells, 1.5L gets us 125 billion cells, and 2L gets us 140 billion cells! (Note: that’s still 40 billion cells less than a 1L starter with a stir plate, but I I think I’ve made my point there…)

A mild mathematical interlude

It’s time to kill the mood with a little math. Your 1L starter netted you 70 billion new yeast cells (on top of the 37 billion you already had). Your net profit from the 1.5L starter was 88 billion new yeast cells. The 2L starter netted you 103 billion new yeast cells. When you look at the number of yeast cells netted per mL of starter, you see a trend:

70 billion new cells / 1000mL = 70 million new cells/mL

88 billion new cells / 1500mL = 58.7 million new cells/mL

103 billion new cells / 2000mL = 51.5 million new cells/mL

While the number of cells is increasing as we make larger starters, the ratio with which they are increasing is, well, decreasing. Actually, if you play with the calculator you’ll see that the yield on a 200mL starter is 120 million new cells/mL. While this is highly efficient, it would require many steps at that size in order to hit your target pitch rate.

The problem with many small steps is that each step increases the risk of contamination (we’ll talk about the importance of sanitizing in Part II of this post). Your goal is to get your target pitch rate in the fewest steps possible, given the size limitation of your equipment. This is why I have vessels in several sizes for doing starters (two 2L vessels, as well as a 5L vessel for large starters).

Step 3: Determining Your Number of Steps

We’ve done a 1.5L starter, we’ve agitated the vessel, and now we’re sitting on 125 billion little yeasties. We still need to get to 520 billion cells. We can start by adding another step:

Step 2 - 1.8L Starter

You can see we’ve added another step: a 1.8 L starter. We’re still shaking or swirling the starter to agitate it. We now have 286 billion cells. We’re over half way there! Let’s try adding one more step:

We did it! Our final total is 527 billion yeast cells. That’s the equivalent of almost 6 smack packs or vials from the store, and all it took was about 550 grams of DME and some time and effort. For reference, a 3 pound (about 1360gms) of suitable DME is about  eleven bucks online, so the total cost of your DME is about $4.50. That gets you the equivalent of 6 packs/vials of yeast (about $30 for the five extra packs/vials). Your yeast starter just saved you $25 and made your beer a whole lot better.

Step 4: Executing Your Plan

Now you know your target pitch rate, you have a plan for how many steps and how big each step will be, and you’re ready to start making some yeast! The only thing left to do is… everything else. Grab your calculations, gird your loins, and check out our next post: Making a Yeast Starter.


Last updated: May 23, 2014 at 10:02 am

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