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How to Make the Perfect Yeast Starter

Happy, healthy yeast is one of the biggest factors in making great beer. And making a yeast starter is the best way to give your wort the happy, healthy yeast it needs to become great beer.

So, what is a yeast starter? It is just a small batch of beer where you grow (or propagate) yeast by giving them the nutrients that they need to reproduce to a number that is adequate to ferment your wort.

Making a starter is not just the province of advanced brewers. There are a lot of different reasons you might need or want to make one and in this article, I’ll explain why. We’ll also look at ways to keep your yeast happy and how to make the perfect yeast starter using packaged liquid yeast or even bottle conditioned beer.

How to Make the Perfect Yeast Starter

Why Make a Yeast Starter?

So, one of the first questions most new brewers ask is “why go to the trouble of making a yeast starter when you could just use packets of dry yeast to ferment your beer?” And the answer is: you could. But it’s not optimal.

For one thing, with dry yeast, it can be hard to determine how fresh or viable it is. It’s not uncommon for it to be old or dead, especially if you’re using the generic stuff that often comes with a kit.

Secondly, with dry yeast, you are a lot more limited in terms of the strains available.

Liquid yeast packets offer a greater variety of strains which gives you more creative latitude and the ability to tailor your beer to a particular style.

And even though manufacturers make packets of yeast that can ferment a 5-gallon batch of wort under 1.060 gravity, you may run into situations where you need more yeast than what is provided (around 100 billion yeast cells per package is common). For higher gravity beers you’ll often need a lot more than this.

Also, there are cases where some strains are offered in yeast slants, which is just a tube with a small amount of yeast cells living on some agar or some other growth medium. In these cases, you’ll be starting with a lot less than 100 billion cells.

Of course, you could simply buy multiple packages of liquid yeast, but this can become costly, particularly if you venture into larger batch sizes.

Additionally, even though liquid yeast is thought to be better than dry yeast there can be issues with yeast health if it hasn’t been properly stored or is approaching or past its expiration date.

Making a yeast starter allows you to grow however much yeast you need in order to ferment your wort. And even more importantly, by controlling how the yeast is grown, you are ensuring that the yeast is clean, healthy and ready to do its job well.

Lastly, a yeast starter is a way to revive old yeast that you aren’t sure about. By testing or proofing the yeast in a starter, you can determine whether it’s still healthy and uncontaminated.

It’s far better to ruin a small starter batch than to run the risk with your whole batch of beer you’ve spent time and money carefully creating.

Propagating Yeast

So you’ve been sold on the value of making a yeast starter and are ready to dive in. But before we get into the step-by-step, it’s helpful to understand how to ensure healthy yeast propagation, and how to determine the right amount for the job.

Yeast Health

Making the perfect yeast starter isn’t just about increasing the number of yeast. The quality of the yeast is as important a factor in brewing great beer as quantity.

By making a starter filled with clean, healthy yeast you ensure that the fermentation of your wort will get off to a fast start and finish quickly. This means there is less probability that wild yeasts or bacteria can get a leg up in your wort.

Quick fermentation also results in a cleaner tasting beer with fewer esters, phenols and other byproducts of yeast metabolism that can contribute to off-flavors. Overall, you’ll get a crisper, drier beer, and you’ll lessen the possibility of under attenuation or stuck fermentation.

In order to get your yeast off to the best possible start in life, it’s important to understand a few basics of yeast health and behavior.

First, yeast needs enough food and nutrients to grow and reproduce. This is why it’s important to make starter large enough to feed the yeast that you are starting with. Too small of a starter means less room for growth because the yeast use up the available nutrients thus limiting how much they grow.

On the flipside, too large a starter is also very hard on yeast. Giving your yeast too much work to do is stressful. Stressed yeast does not equal happy, healthy yeast.

Even osmotic pressure affects yeast, and too much can have detrimental effects, which is why the specific gravity of most starters should be between 1.030-1.040. If you are starting with a very small amount of yeast or it’s of questionable viability and health, start with an even lower gravity of around 1.020, because higher gravity worts can be too stressful for it.

Secondly, oxygen is critical to yeast growth. Eight to 12 ppm of oxygen is recommended for most yeast strains. And because boiling liquids drives of oxygen, it’s important to thoroughly aerate the wort before adding yeast. For a small starter, vigorous shaking should do the trick. Using a stir plate with a stir bar is even more effective.

Furthermore, the rate or speed of growth of yeast is very dependent on temperature. Ideally, you want to keep your starter between 70°-75°F (21°-24°C) for best growth. Once the yeast is ready to pitch, it is important that the temperature is similar to or cooler than the wort it’s being pitched to.

If you pitch a warm starter to cool wort it can slow the start of fermentation or put the yeast to sleep. Pitching from cooler temperatures to warmer is not an issue, and in fact, many brewers favor “cold pitching” which means pouring the starter straight from the refrigerator to wort that is several degrees cooler than the optimum fermentation temperature for the yeast strain.

Just remember: yeast is very adaptive to all aspects of its environment. So if the conditions of your starter culture are very different from the wort it gets pitched into, it can stress the yeast.

And lastly, any discussion of yeast health would not be complete without mentioning sanitation. It’s important to brewing great beer, and essential when propagating yeast. Sanitize, and/or sterilize anything that will come in contact with your starter yeast. This will ensure they stay healthy and clean.

Determining Optimal Yeast Pitching Rates

One of the first things you need to do before making your starter is to determine the pitching rate, or approximately how many cells of yeast are required to ferment your batch of wort. Pitching rates will vary based wort specific gravity as well as the style of beer you are brewing.

Pitching rates are usually given in terms of number cells per milliliter or liter per degree Plato (or 4 gravity points).

For instance, let’s say a particular beer style calls for a pitching rate of 1 million cells per milliliter per degree Plato (which is the same as saying 1 billion per liter) and the wort has a specific gravity 1.040 (which is equivalent to 10 degrees Plato).

We will need around 10 billion yeast cells for each liter in our batch, or 10 degrees Plato x 1 billion. If a liter is about a quart then there are about 20 quarts or liters (actually more like 18.9 but for simplicity’s sake we are estimating) in 5 gallons (since that’s a common batch size). So, at this pitching rate, we’d need about 200 billion cells to ferment 5 gallons (20 liters) of wort at 1.040 original gravity.

Whew! I know that’s a lot of math. The good news is there are a lot of charts available to do all this work for you. But, it’s important to understand the underlying logic of how pitching rates apply to batch size and wort gravity.

Now that you understand what pitching rate measures, it’s important to realize that optimal pitching rates are usually given as a range. And while heavier beer (more fermentables/higher gravity), requires more yeast than a lighter beer, the optimal amount will vary for different styles of beer. Do a little research on whether the low, medium or high end of the pitching rate range is best for the style of beer you’re brewing up.

“Tailor your pitch rate to the style of beer that you are brewing.”

For example, John Palmer, in his book “How to Brew”, recommends between 0.5-1 billion cells per liter per degrees Plato for ales, and 1-1.5 billion for lagers.

As Palmer explains, using the lower end of the pitching rate range often results in a higher initial growth rate and more by-products of yeast metabolism, such as esters and phenols which may be appropriate for certain styles. Using the higher end of a pitching rate recommendation tends to yield a cleaner taste with a less fermented character.

Starter Size: How Big is Big Enough?

Once you know your target pitching rate, you’ll need to consider starter size. This is the overall volume of the mini-batch that you will pitch to your wort.

Your yeast starter size should be determined by how many cells you are beginning with and how many you ultimately need for the particular beer you are making.

A frequent recommendation for making a starter with a package of liquid yeast is to aim for 1 liter (~1 quart) of starter. But, this one-size-fits-all approach is not optimal. In fact, many manufacturers recommend making at least a 2-liter starter for a 5-gallon (~20-liter) batch if starting with a package of liquid yeast that contains around 100 billion cells.

And, of course, you may need an even bigger starter depending on beer style, starting gravity and batch size.

For instance, a typical liquid yeast like the PurePitch® package made by Wyeast contains anywhere from 60-120 billion cells, according to their website. Putting that into a 1-liter starter should double in a day, but making a 2-liter starter will yield about two and half times the initial amount. Putting the same yeast in 3 liters will triple it in size. So, the growth rate is related to starter size.

There is a point of diminishing returns, however. Putting a very small amount of yeast in a very larger starter culture is not good for the yeast and will yield less than optimal results. There are charts available to help you determine the growth rate of yeast based on starter size.

Bottom line, it’s important to understand where you are starting and where you want to go. Then you can estimate how much starter wort you need to make up based on the growth factor of the yeast.

How to Make a Yeast Starter from a Liquid Yeast Packet

Now that we’ve gotten some theory out of the way, let’s look at the step-by-step. Keep in mind you’ll need to make your starter 1-2 days in advance of brew day.

Equipment You’ll Need:

NOTE: If using yeast with an inner nutrient packet, take it out of the fridge about 4 days before brew day, and burst it by squeezing the inner packet. Shake it up and let it rest overnight in a warm place until the packet has fully swollen.

Make a Yeast Starter a Few Days Before Brew Day

  1. Add 2 cups DME (7 oz or 200g) to 2 quarts (or water to equal 2 liters total volume) of water either in your pot. Stir and boil for 10 minutes. (A flask can be boiled directly on the stove if you have a gas stove, but we recommend using a separate pot to minimize boilovers. But if you use a flask, do not use it on an electric coil stove)
  2. While your wort is boiling, clean and sanitize your flask. For added insurance, you can put the flask in the oven at 250°F for an hour. Place a piece of foil over the top if you do this.
  3. Put a lid on it during the last few minutes of the boil to sanitize the lid. Be careful of boilovers.
  4. After the boil is finished, add ⅛ tsp complete yeast nutrient with zinc to the mixture.
  5. Using a funnel in your flask over the sink, pour the hot wort into the flask (if using a stir bar, toss that in to sanitize).
  6. Submerge the flask in an ice water bath. Cover with sanitized foil. Use a flask weight, if you have one, to keep the flask bottom submerged.
  7. Use an oven mitt to swirl around the wort frequently so that it cools quickly in the ice bath to 65°-75°F.
  8. Once the wort has cooled, sanitize outside of the yeast package and pour the yeast into the flask. Swirl to combine.
  9. If using a stir plate, place flask on the plate and turn it on. Put the whole thing somewhere out of direct sun and that has a steady temperature between 70°-75°F.
  10. If you’re NOT using a stir plate, shake vigorously for about a minute. And periodically swirl around the starter for the next day or two. Be careful because the starter can foam up and out of the flask if you stir too vigorously after fermentation has begun.

NOTE: For larger batches or high gravity worts, the starter process can be repeated as many times as needed until you have enough yeast to pitch.

How to Make a Yeast Starter from Bottle Conditioned Craft Beer

When propagating yeast from bottled beer, you will need to start with a smaller starter size than usual. Also, the specific gravity of the wort should be less, around 1.020 OG, because higher gravity wort will overtax the yeast cells.

Equipment You’ll Need:

You’ll need the same equipment listed above to make this smaller starter, but instead of a fresh package of liquid yeast, you’ll need 2-3 bottles of bottle-conditioned or unfiltered canned craft beer.

Make a Yeast Starter From Your Favorite Bottled Beer a Few Days Before Brew Day

  1. Add 20g DME (approximately 1 Tbsp) plus enough water to equal 400ml (or add 2 cups water for English measure) in a pot and swirl to combine. Your starting gravity should be around 1.020.
  2. Boil wort 10 minutes.
  3. While your wort is boiling, clean and sanitize your flask. For added insurance, you can put the flask in the oven at 250°F for an hour. Place a piece of foil over the top if you do this.
  4. Put a lid on it during the last few minutes of the boil to sanitize the lid. Be careful of boilovers.
  5. After the boil is finished, add a pinch of complete yeast nutrient with zinc to the mixture.
  6. Using a funnel in your flask over the sink, pour the hot wort into the flask (if using a stir bar, toss that in to sanitize).
  7. Submerge the flask in an ice water bath. Cover with sanitized foil. Use a flask weight, if you have one, to keep the flask bottom submerged.
  8. Use an oven mitt to swirl around the wort frequently so that it cools quickly in the ice bath to 65°-75°F.
  9. While the wort is cooling, use a small solution of Star-San in a spray bottle to sanitize the bottle tops and then cover with foil that has also been sanitized.
  10. When wort has cooled to 65°-75°F, remove the foil from bottles, swirl to create a slurry, and then decant the yeast from the bottles into the starter wort.
  11. Put the flask on your stir plate, and turn it on. Keep your starter out of direct light and in a place that is 70°-75°F.
  12. Turn the stir plate off after 12-18 hours or about half the estimated propagation time. This will give the yeast time to build up its reserves before pitching.
  13. Within 24-48 hours, you should see the yeast settle out and propagation will be complete.
  14. In order to make a big enough starter, it’s advisable to step up this starter with at least one more addition of starter wort.
  15. In order to do this, simply make another batch of wort, this time using 200g DME (~7 oz) to enough water to equal 2 liters total volume (or ~2qts), to give a specific gravity of between 1.030-1.040. Add a pinch of complete yeast nutrients.
  16. Cool the wort as before and add this to your initial starter and swirl to mix. Place starter back on the stir plate and follow the above procedures again.
  17. Once you are ready to pitch to your batch (if doing 5 gallons), cool the wort in the fridge and either pitch the full amount to your wort or decant and pitch (as described below).

When to Pitch Your Yeast Starter

A yeast starter is ready to pitch when it is at full activity (or high krausen), but many brewers favor waiting until the yeast has settled out. Krausen is the foamy layer that forms as yeast ferments the wort. This may or may not appear, depending on a number of factors.

Depending temperature and the size and pitch rate, the starter will be ready between 24-48 hours.

It will be good for pitching up to 2 days after the yeast settles. Any longer than that, you may need to replenish the starter.

After yeast ferment, they store up reserves of food that they use while inactive. So, if you wait too long to pitch the starter, the yeast may have used up these reserves which makes them less able to handle the stress of fermenting your wort.

To replenish yeast, make another starter wort as before and add it to the initial starter, allowing it to ferment again before pitching.

Decanting vs. Adding The Whole Starter

When you are ready to pitch the starter, you can simply pour the whole shebang into your wort. Usually, the effect on your wort is minimal to none. But, if you’re brewing a very light bodied beer or are using a very large starter and you are concerned about the effects of the starter wort on your batch flavor or the original gravity, then you can decant the starter before pitching.

Decanting is easy to do. Simply put the starter in the fridge overnight after it has fermented, and allow the yeast to settle fully. Then, just pour off most of the wort, being sure to leave the layer of yeast at the bottom. A little bit of wort isn’t going to hurt your beer and will ensure you aren’t pouring off the yeast. Swirl the slurry and pitch to your wort!

Are You Ready To Make a Yeast Starter For Your Next Batch of Beer?

Making the perfect yeast starter for your beer doesn’t require a degree in biochemistry, just a basic understanding of yeast behavior and some nuts and bolts of propagation. I hope this article will give you the confidence to try it. Your beer will thank you!

Happy Brewing!

How to Make the Perfect Yeast Starter

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