What You Need to Know About Yeast

Yeast can be such a confusing thing, and it’s so crucial to the success of your beer, I felt it was important to get a few things straight. In golf, they have a saying , “You drive for show and putt for dough.” Putting is to golf as yeast is to homebrewing… really important!!

Rehydrating vs. a Starter

Before diving into all this, let’s clear up the difference between a rehydration and a yeast starter.

  • Rehydrating yeast: Rehydrating yeast is done to bring dry yeast out of the suspended state it’s in using plain water. You would obviously never do this with liquid yeast.
  • A Yeast Starter: A yeast starter is made to increase the yeast population before pitching.

Yeast Count

You want to pitch the right amount of yeast in whatever beer you’re making, and this is pretty easy to do. For every beer that I make, I visit Mr. Malty’s Yeast Calculator. The user interface ain’t pretty, but it was created by Jamil Zainasheff who is a homebrewing legend and it’s a valuable tool that takes one minute to use.

Using Mr. Malty:

  1. Select your fermentation type in the top left corner. If you’re not sure, you’re probably making an ale.
  2. Enter the expected OG of your wort (or the actual OG if you know it). If you’re making beer from a kit from the store, this is in the top left of the instruction sheet.
  3. Set the volume of wort (normally 5 gallons).
  4. If you are using dry yeast, click the “Dry Yeast” tab. This will tell you how many yeast cells you need, and how many packets of dry yeast you need (depending on whether you’re using 5g or 11.5g packets) without a starter.
  5. If you are using liquid yeast, click the “Liquid Yeast” tab, then select “Simple Starter” in the drop-down that appears. This tab page will tell you how many yeast cells you need, and how many packets of liquid yeast you need, depending on whether you’re making a starter or not.

Now that you know exactly how much yeast to pitch, let’s figure out what to do with it.

Dry Yeast

From Mr. Malty’s calculator, for a beer with an OG of 1.06, one 11.5g packet of dry yeast without a starter is perfect. This is good news, you don’t have to make a starter! Unfortunately, when we use dry yeast, the question of whether to rehydrate the yeast or not comes up.

Rehydrating the yeast

From our definition before, we know that rehydrating dry yeast is not the same thing as making a starter. We rehydrate yeast to bring it out of the suspended state it’s in. From John Palmer’s page:

Often the concentration of sugars in wort is high enough that the yeast can not draw enough water across the cell membranes to restart their metabolism.

Therefore, using plain spring water is the best way to do this. It ensures that your yeast are in the healthiest condition possible when they’re introduced to your wort. If you are unsure of how to rehydrate yeast, there is an excellent video by Northern Brewer here that demonstrates exactly what to do.

Not everyone agrees that you need to rehydrate yeast before pitching it. Brewer’s Best recipe sheets say specifically, “Sprinkle the contents of the yeast sachet over top of the entire wort surface (DO NOT REHYDRATE)”. Fermentis, a very popular dry yeast manufacturer, says you can rehydrate it or pitch it directly, they don’t care. Bulosophy, an excellent source of homebrewing “exBEERiments” and results, concluded that rehydrating vs. pitching directly made no difference.

So what’s going on here? I would say that the biggest takeaway here is that in practice:

  1. You don’t have to rehydrate your yeast. However, if you do, you’ll get a larger, healthier yeast population being pitched into your wort. This will get the fermentation started faster… I never like to stress my yeast out.
  2. You don’t need to make a starter, because the yeast count in an 11.5g packet is typically enough.

Liquid Yeast

Obviously, liquid yeast require no rehydration… they’re already hydrated, it’s liquid! Remember our cell count per packet, though, and how we want to pitch the right amount of yeast? Let’s compare dry yeast and liquid yeast packets:

That’s a huge difference! When you get a packet of liquid yeast, you are getting less than half of the yeast cells than you get in a dry packet.

Making a Yeast Starter

100 billion cells is often not nearly enough yeast to pitch in a 5 gallon batch, and that’s why we often make a starter when using liquid yeast. As I said earlier, making a starter increases the cell population, potentially doubling it. Therefore, when you use liquid yeast, you have two options:

  1. Make a starter (less expensive)
  2. Pitch two packets (less work)

If you’re not familiar with how to make a starter, Kyle from the store has written up an excellent description of what to do.


As they say on the internet, TLDR. Here are the important things to take away from this blog post:

  1. Always check how much yeast you need by using Mr. Malty.
  2. If you use dry yeast…
    • You don’t need to rehydrate it, but it will get your fermentation started faster.
    • You rarely need a starter.
  3. If you use liquid yeast…
    • You are getting less than half of the yeast than you get in a dry packet.
    • You will almost always want to either make a starter from a single packet, or pitch two packets, for a 5 gallon batch.
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