Mr. Malty Pitching Rate Calculator

The Mr. Malty Pitching Rate Calculator helps you determine the right amount of yeast to pitch for any batch of beer. It supports liquid yeast, dry yeast, and repitching from slurry — from any manufacturer. You can adjust pack sizes, enter production or best-by dates to estimate viability, and calculate starter sizes for a variety of methods.

All of the classic Mr. Malty calculations are here, along with some new formulas that represent a more optimistic outlook for yeast that has been well transported and stored. The app is free with minor ads, or you can remove them with a one-time purchase.

How to Use the Calculator

The calculator starts on the main screen, and is mostly self-explanatory, but here are some tips that may help.

Up at the top of the screen is the Results section. This tells you how much yeast you need to properly ferment your beer. This calculation is based on the amount of wort, the specific gravity of the wort, and the strain of yeast.

Depending on your settings for yeast type, the results will list the amount of slurry needed, the number of packs without a starter, and the starter size.

Yeast Cells Needed (in Billions)

For all practical purposes, most homebrewers won't need to know this number, because it is difficult to count the cells without a microscope. Instead, most brewers assume the predicted amount of yeast from a given sized starter is correct.

Vials or Packs Needed Without a Starter

This is the number of yeast packages needed without making a starter. If this number is one (1) or less, there is no need to make a starter. If this number is greater than one (1), and you do not make a starter, this is the amount of packages you need to pitch in order to properly ferment the beer.

Starter Size

The starter size shown is the total volume of wort for your starter. When the calculator recommends more than one pack, pitch all of the packs into the same starter — the volume shown already accounts for the additional yeast.

Vials or Packs Needed With a Starter

Using the numbers you entered, the program calculates the number of yeast packages needed for the starter. In bigger beers or larger batches, a starter with just one package may not produce enough cells to properly ferment your beer.

Settings Menu

The menu at the top right (three dots) contains the Settings, Remove Ads, and About links. Your main use of this is to change the units of measure used in the application.

Yeast Strain

This is your first setting. Select whether the yeast you are using is Ale, Lager, or Hybrid. The difference here is the pitching rate used. Ale is 0.75 million cells per milliliter per degree Plato. Lager is 1.5 million, and Hybrid is in between at 1.0 million. The default is Ale.

Specific Gravity and Volume

Next, enter the specific gravity and volume of the wort you plan to ferment. The defaults are 1.050 OG and 5 gallons (or 20 liters if your device is set to metric).

Yeast Date and Viability

At this point you can choose to enter the yeast manufacturing date, which should be on each package of yeast. Sometimes it is listed as a "Best By" date. This is highly recommended unless you can measure the yeast viability yourself. If you know the viability, you can enter it in the % Viability field when Use Date is deselected. By default, Use Date is off and viability is set to 97% for liquid yeast, 90% for dry yeast, and 95% for repitch.

Viability is a measure of yeast health. Yeast viability depends a lot on how it is handled and it can drop off very rapidly when shipped or stored improperly in overly warm or cold temperatures. While the yeast companies work miracles in creating vital, healthy yeast, they do become less vital over time even under the best of conditions. The date your yeast was packaged should appear on your package. Some manufacturers prefer a "Best By" date. For example, White Labs' best by date is 7 months from production for ale and lager yeasts (6 months for Brettanomyces and bacteria products).

If you are repitching your yeast, use the date at which you harvested your yeast and the application will calculate the remaining viability. While the exact viability of the yeast cannot be known without at least a microscope, hemocytometer, and stain, it is possible to estimate it. The formulas used in this application to predict growth and decay rates were developed through extensive laboratory research and real world experience. The transportation and storage of yeast can have a big impact on viability before it reaches you. In order to protect your investment in materials and time, we use a more pessimistic model than some others with the goal of ensuring your beer always turns out great. In this new calculator we have included an optional new model that assumes more optimal conditions for transportation and handling. You can select which model to use once you select a package date. If you wish, you can override the models to enter your own viability percentage.

Yeast Form

Next, select your yeast format. Are you using wet or dry yeast packages? Or are you repitching your yeast from a previous batch or perhaps a yeast pitch from another brewer? The default is Liquid Yeast.

Starter Type

If you are making a starter, select your starter type. You can select Simple Starter, Simple with O2 at Start, Intermittent Shaking, Continuous Aeration, or Stir Plate. The default is Simple Starter. Like the decay models used in the application, the growth model was extensively measured and tested to provide consistently reliable results. While others may have used our application to mimic this first-of-its-kind model, the current application uses the actual Mr. Malty growth model.

• Simple Starter: This is just adding yeast to wort and letting it do its thing. This will produce the least amount of yeast.
• Simple with O2 at Start: Oxygen is a vital component in yeast growth. It is used to create sterols that aid in cell membrane pliability, which is important for the ability of the yeast to bud. An initial shot of oxygen can help produce more yeast.
• Intermittent Shaking: Shaking the starter every hour or two can drive off built-up carbon dioxide, introduce a little more air, and ensure that the yeast have access to any sugars left. This is a fairly inexpensive way to increase the results of your starters.
• Continuous Aeration: Adding air into your starter provides the yeast with more oxygen and also drives off carbon dioxide, which can suppress yeast activity. Just be certain that the air added is sterile. In-line air filters are available at most homebrew shops.
• Stir Plate: The stir plate is an excellent way to get the most out of a starter. The action of the stir plate drives off carbon dioxide, introduces more air, and ensures that the yeast have access to any sugars left. When you use a stir plate you do not need to run it at the highest speed. Turn it up until you see a slight dimple form in the starter liquid. Excessive speed can damage some yeasts and is unnecessary.

Stepped Starter

If the recommended starter volume is larger than your flask or carboy, you can use a stepped starter to build up the yeast in stages. Tap the "Stepped Starter" link in the results section to open the stepped starter calculator. Enter the wort volume you can make per step, and the calculator will determine how many steps it takes to reach your target cell count.

Each step works like this: you make a starter at your chosen volume, let it ferment for a day or two, then cold crash it in the fridge. The yeast will settle to a compact cake at the bottom. Pour off the spent liquid and add fresh wort on top of the yeast cake. That is your next step. Repeat until you have enough yeast.

The stepped starter always starts with a single pack of yeast. The calculator shows the volume and resulting cell count for each step. On the last step, you may not need the full volume — the calculator will tell you exactly how much wort to add.

Growth Rate

Below the starter type is a Growth Rate slider (default 3.0, range 2.0 to 6.0). This controls how many times the yeast cells are expected to multiply during a starter. At the default of 3.0, each pack is expected to produce three times its initial viable cells through the starter process. A higher growth rate means fewer packs are needed to reach your target cell count. If you are confident in your starter technique and sanitation, you can increase this value. If you want a more conservative estimate, lower it. This setting only applies to liquid yeast.

Advanced Settings

There are Advanced settings at the bottom of the screen for each yeast format type.

Liquid Yeast

For liquid yeast packages you can enter the amount of cells per pack. The default is 100 billion for the wet yeasts. This is the guaranteed minimum the manufacturers promote. Yes, there might be more yeast than 100 billion. If you have access to the production data for the specific package you are holding (often provided automatically to commercial brewers purchasing larger pitches), you can enter it here. Otherwise use the default.

Dry Yeast

For dry yeast packages you can enter the amount of cells per gram and the package size. There are two sizes that are common (defaults are 5g and 11.5g), but with the proliferation of dry yeast packs, you can enter whatever you like. The default is 10 billion cells per gram. We have measured everything from 8 to 20 billion cells per gram for dry yeasts. Some of the material in the dry yeast pack is not yeast, but rather for keeping the yeast from clumping and making packaging easier. If you have access to the production data for the specific package you are holding, you can enter it here. Otherwise the default is safe.

Note that the dry yeast viability decay model in this calculator has been updated from the original simple linear formula. The new model is more conservative — it predicts lower viability at a given age than the original — reflecting more realistic storage and handling conditions. This means the calculator may recommend more yeast than older versions of the app did for the same package age.

Repitch Yeast

When harvesting yeast from a previous batch, the thickness of the slurry and the amount of non-yeast material will vary. The defaults are 2.5 billion cells per ml for yeast concentration and 15% for non-yeast material. In general, these defaults will give you excellent results, but if you have an accurate measurement or fear that your yeast is too liquid, you can change them here. For the vast majority of users, the defaults should be very close.

To give you some idea of what a thick slurry is, consider this. If you've ever seen the yeast packed hard into the bottom of a White Labs vial from many months ago, that is around 4.5 billion cells per ml. When you harvest a yeast slurry and it has settled for a few hours, that is a thin slurry. Usually, most homebrewers will let their yeast settle for a week in the fridge between one batch and the next. When you do, you'll notice the yeast has settled a bit and has become denser. The default setting on the calculator approximates that.

Once you've determined how much yeast you have in the container, you can shake the container along with any liquid to loosen up the yeast for pitching. For example, let us say you have 200 ml of yeast solids in your yeast storage container and you want to pitch 100 ml of it. Shake the container to break up the yeast and then pour 1/2 of this now very loose yeast slurry into your beer. That is still 100 ml of yeast solids, even with the additional liquid.

FAQ

Do I really need this much yeast?

The Mr. Malty Pitching Rate Calculator is designed to give you optimal fermentation performance for the very best beer. Yes, you could probably get away using a little less yeast, but why risk all that expensive malt, hops, and time?

Am I at risk of under- or over-pitching my beer?

Yes and no. If you use the calculator, you should never end up under- or over-pitching your beer. Keep in mind that under-pitching can be worse than over-pitching and it is much harder to over-pitch. In the end, the correct pitch rate is based on results. If a lesser or greater amount produces the best beer for you, then that is the "proper" pitching rate.

What is the source of this information?

The original Mr. Malty Pitching Rate Calculator was created by Jamil Zainasheff based on independent laboratory research and discussions with Greg Doss at Wyeast and Chris White at White Labs. Many repeated tests on samples purchased from a variety of sources and handling conditions provided the majority of the data. The growth model was painstakingly developed through many tests over the course of approximately one year. Concurrently, Doss had been doing similar work at Wyeast and he was able to confirm Jamil's growth model.

How do I use this for something other than White Labs or Wyeast?

You should be able to use this calculator for any yeast product available if you know the size of the package and the amount of yeast. Usually the manufacturer will share their averages with you and you can enter it in the application. If not, going with the defaults should work out for the majority of yeast products out there.

How do I get rid of the ads?

In the menu at the top right (three dots) there is an option to remove the ads with a one-time purchase.

Who is the developer of this app?

The original version of this application was developed by Jamil Zainasheff sometime in the early 2000s. The current version was developed by Lee McDole with assistance from Jamil Zainasheff and Travis Combel. The application is published by McDole Group, LLC.

Is this really the official Mr. Malty app?

Yes. Mike "Tasty" McDole was a dear friend of Jamil Zainasheff, and Jamil is happy to pass along the stewardship of the application to Lee McDole.

Where do I find the date for viability?

Every yeast package has a date on it. Some include the production date, which is ideal. Some use "Best By" dates. These are usually 7 months from production for White Labs liquid products and one year for most dry yeast manufacturers. When in doubt, ask the manufacturer.

What is a slurry?

After fermentation and harvesting the beer, the yeast left over is often referred to as a slurry of yeast.

Which starter type should I use?

Ideally, use a stir plate, but at the least use a shaken starter if money is tight.

How do I make a starter?

There are many videos and articles on making a starter. It is covered extensively in Yeast by Chris White and Jamil Zainasheff and also on the Mr. Malty website: https://www.mrmalty.com/pitching.php

Should I change the default Yeast Concentration or Non-Yeast Percentage sliders?

If you know that your slurry has special conditions, yes, but generally the default will work in 90% of all repitching.

Can I use this calculator for wine or mead?

Yes. Use the Ale setting.

Can I use this calculator for bacteria?

Not really. The growth rate, decay rate, and pitching rates for bacteria are different than yeast. Maybe, if you all support this app, I will make one for bacteria.

Can I use this calculator for Brettanomyces?

Yes, but while Brettanomyces is a yeast, it can behave differently. Growth should be the same, but pitching rate may vary depending on what you are trying to achieve.