## 1. Calculate the size of the Yeast

How do you make a yeast starter starting with liquid yeast? Well, that’s what I’m about to show you with this step-by-step guide!

Before you can start you need to know **how big** the yeast starter needs to be. In order to do this, you can find different tools on the internet like for example Brewersfriend Yeast Pitch Rate and Starter Calculator.

This calculation is made out of 2 parts. First, we need to calculate the number of needed yeast cells with this first tool:

**Wort Gravity OG:**The heavier your beer, the more yeast cells you will need. This value is retrieved from your recipe. This value can be in OG (Original Gravity) or in °Plato, the unit you want to use needs to be selected at the top of the calculator.**Wort Volume:**The more wort, the more cells you need. You can find this value in your recipe.**Target Pitch Rate:**This value represents the number of cells per milliliter starter that you want to achieve. We will use the following rule: For ales below 1.060, we will use 0.75, everything above 1.0, multiply this value by 2 for lagers. More info about this topic can be found here.**Yeast type:**In this case we will choose liquid yeast.**Liquid packs:**The more packages you use, the smaller the starter will need to be.**Viability:**Or the health of your liquid yeast pack. The older the yeast, the less healthy the yeast will be. We only need to fill in the production date (Mfg date) of the package and the calculator will determine the viability.

When all these values are filled in, click « update ». Next the tool will calculate the difference between the needed cells and the available cells. This number is the amount of cells we will need to grow. In the example this is 132 billion cells!

In most cases you will need a starter, so we continue to the next step. Scroll a bit down on the page and you will see the second calculator. With this tool we will calculate the needed volume of the starter:

**Starting yeast count:**This is the number of cells we calculated with the previous tool. By clicking « Grab from above », the value will be copied automatically.**Starter size :**Depending on the number of cells we need to grow, we will need a certain starter volume (more on this later).**Gravity:**The density of the starter is kept at 1.036 for the optimal growing medium (about 100 gram DME per liter).**Growth model and Aeration:**To make yeast grow at the optimal rate, you will need a magnetic stirplate, this way your starter will grow at the fastest and most efficient rate. The dropdown menu gives you a choice of different growth models. For the use WITH magnetic stirplate, you can choose 2 possibilities. Either the model of C. White or Braukaiser (most recent study). The difference between these models is explained lower on this page. For now we choose the model of Braukaiser**Number of steps:**At the bottom of the calculator you have the option to make the starter in more steps (2 or even 3). I’ll explain this later.

Ok, now that we have filled in everything, how do I know what volume to use for my starter? Well, the gravity of the starter is kept constant at 1.036, if we change the volume of the starter, you will see that the amount of cells we end up with will change as well. Let’s try this for a volume of 0,5 liters and press « update ». In case **« starter meets desired pitching rate! »** appears, we will reach the needed amount of yeast cells at the end of growth with a starter size of 0,5 liters. In case **« Starter does not create enough yeast cells. Increase starter size, change aeration technique, or do another step »** appears, the starter is too small. Keep in mind that the ratio of yeast startervolume can’t be too great compared to the amount of wort we want to ferment. Otherwise we might end up with a beer with off-flavors! (The volume of the starter should not exceed 5% of the wort volume, at the end of the growth cycle you can opt to drain the upper liquid off the yeast starter to decrease the total starter volume, this is explained in the step guide lower on this page).

In the case that the needed starter volume is getting too high, you can choose to make a starter in **multiple steps** as stated before. In this case you check the mark in front of « starter – step 2 » and if necessary « starter – step 3 ». In this case you would put your starter in the fridge whenever the growth cycle is completed to settle out all the yeast cells. Now you can drain the upper liquid so you only keep the yeast cells in your Erlenmeyer. Add a fresh batch of DME (1.036) to your yeast and the calculator will recalculate the amount of cells you will achieve after this extra step (some goes for a third step).

## 2. Necessities yeast starter:

- Light DME (Dry Malt extract)
- Wyeast smackpack or Whitelabs liquid yeast (the fresher, the better)
- Erlenmeyer
- Vortex Magnetic Stirplate + stirbar
- Stove
- Tin-foil

Optional

- Lactic acid (for acidification of the starter)
- pH meter or pH paper
- Yeast nutrients

## 3. Practical implementation yeast starter

Before we start there is 1 very important point that we need to think about: **WORK HYGIENICALLY!** If your yeast starter gist infected at the early stage, you will also grow this infection (wild yeast, bacteria, …). This will almost guarantee a bad end result! If possible, work near an open flame (bunsen burner).

- Weigh the needed amount of DME and add it to the Erlenmeyer (about 100 gram per liter starter, the exact amount is calculated by the tool we used before)
- Optional: weigh the needed amount of yeast nutrition
- Water down the DME until the needed volume of the starter is reached.
- Optional: Correct the acidity to a pH of 5
- Boil the content for at least 15 minutes (you can do this straight on the stove, put a piece of tin-foil on top of the Erlenmeyer).
- Cool down to room temperature (you could use an ice-bath)
- Add the liquid yeast to the Erlenmeyer (in case of Wyeast, the « balloon » inside of the pack can be added as well but there is no need to activate it in advance and let the pack swell up).
- Put the Erlenmeyer 12 to 24 hours on the Magnetic Stirplate between 18 and 24 °C (22 °C is a good balance if you have the option to place the magnetic stirrer in a controlled environment). Now it is important to get a color best described as « coffee with milk ».
- Once this is achieved, you need to cool down the starter for at least 24 hours to make the yeast settle on the bottom.
- Now you can drain the top liquid (best not to pour, otherwise you might stir the yeast back into the top liquid).
**In case of a starter in multiple steps (skip this step when you are making a 1-step starter)**: Add the needed DME-solution (1.036) to the Erlenmeyer (make sure you cooked this before to make sure it is sterile, cool down before adding it to the starter)- Stir the remaining liquid well and let it warm up to a maximum difference of 5 °C compared to your wort.
- Pour the starter in your wort and let the yeast do the rest of the work 🙂

There you go! That’s how you make a yeast starter.

## Extra: Yeast Growth Equations

- The first growth equation is by Kaiser of
**Braukaiser.com**. This model is based on Billions of cells of growth per gram of extract (B/g).Detailed information, including the equation is here.NOTE: The Braukaiser model should only be used with stir plates. For very large starters (+5L) the results may be high as there is no upper growth limit in the current equation.*More data is being collected and we expect to enhance this functionality when the results are in from Kaiser!* - The remaining growth factors are based on an empirical study done by Chris White, which is detailed in:
White, Chris, and Jamil Zainasheff.
*Yeast: The Practical Guide to Beer Fermentation.*Boulder, CO: Brewers Publications, 2010. 139-44. Print. Very interesting lecture!This model is based on an inoculation rate leading to a yeast growth factor. There are some caveats to the model to be aware of.

– The maximum growth factor is 6 (the starter will never grow past that amount).

– The saturation point for a starter is 200 million cells/ml (the starter not grow at that inoculation rate).

– The growth curve is geared for a starter gravity of 1.036 (9 ° P).

– The initial study did not address stir plates or shaking methods. However, anecdotally, aeration and stirring are said to provide positive benefits. We do not have a citation for this unfortunately, but if you can point us towards one we would be happy to update this page and the calculator logic.

– At this point the yeast calculator is quite conservative: no aeration: no adjustment, shaking regularly: +0.5 boost to growth factor, stir plate: +1.0 boost to growth factor.