Yeast Calculator

Determine optimal yeast pitch rates and calculate starter requirements for liquid yeast.

The Yeast Calculator determines optimal yeast amounts and calculates starter requirements for liquid yeast.

Calculate how many yeast packages to add or how big of a starter to make

How to Use

The tool is divided into two sections: Pitch Rate (top) and Yeast Starter (bottom).

Pitch Rate Section

Input	Description
Original Gravity	The target OG of your wort
Volume	Post-boil volume into the fermenter
Pitch Rate	Select a preset or use the slider to set a custom rate (million cells / ml / degree Plato)
Yeast Form	Choose between Dry or Liquid yeast

Pitch Rate Presets

The pitch rate selector offers these presets:

• 0.35 -- Minimum

• 0.75 -- Ale up to 1.060

• 1.00 -- Ale 1.060 or more

• 1.50 -- Lager up to 1.060

• 2.00 -- Lager 1.060 or more

A slider allows fine-tuning the pitch rate from 0.35 to 2.50.

Dry Yeast Inputs

When Dry is selected, these additional inputs appear:

Input	Description
grams per pkg	Weight of yeast per package (default 11.5)
Billion cells per gram	Cell density of the dry yeast (default 13)
Rehydrate	Checkbox to indicate whether you plan to rehydrate the yeast

Liquid Yeast Inputs

When Liquid is selected, these additional inputs appear:

Input	Description
Billion cells per pkg	Cell count per liquid yeast package (default 100)
Calc viability	Checkbox to automatically calculate viability from the manufacturing date
PurePitch	Checkbox for White Labs PurePitch packets (uses a different viability curve)
Manufacturing date	The yeast package manufacturing date
Viability	Percentage of viable cells (auto-calculated when "Calc viability" is checked, or enter manually)

Pitch Rate Output

The output card shows:

• Target pitch -- the total billion cells needed

• Yeast to use -- number of packages needed (rounded up), with the fractional value shown for reference

• Billion cells total -- the actual cell count from the recommended number of packages

• Target diff -- how many billion cells above or below target

Yeast Starter Section

The starter section calculates how large a starter you need to grow enough cells.

Input	Description
Start amount	Number of packages or billion cells to begin the starter with (toggle between "Packages" and "Billion cells" modes)
Overbuild	Extra billion cells to grow beyond your pitch target, for harvesting and saving for future brews
Growth Model Formula	Choose between No Stir (Chris White) or Stir (Braukaiser)
Calc starter size	Checkbox to let the tool automatically calculate the optimal starter volume

Multi-Step Starters

The tool supports up to 10 starter steps. Use the Add step and Remove step buttons to manage steps. Each step has:

Input	Description
Gravity	The gravity of the starter wort for that step (editable when using the Braukaiser model; default 1.036)
Size	The volume of the starter step (auto-calculated when "Calc starter size" is checked, or enter manually)

Per-Step Output

Each step displays a result card showing:

• Step number (when multiple steps are present)

• Starter volume and required DME amount

• New count -- the total billion cells after this step (color-coded: green when target is met, yellow when close, red when insufficient)

• Difference vs target pitch rate in billion cells

• Pitch Rate -- million cells / ml achieved

• Inoculation Rate -- million cells / ml (ideally between 25 and 100 for best growth)

• Growth Factor -- ideally at least 1.0

When Overbuild is set, each step additionally shows:

• Overbuild Harvest -- the volume and percentage of the starter to harvest and save

• Pitch Amount -- the volume to pitch into your wort

Each step also shows the Liquid Malt Extract equivalent alongside the DME amount.

Recommended Pitch Rates

By Beer Type

• Ales: 0.75 million cells/ml/°P (standard)

• Lagers: 1.5 million cells/ml/°P (double ale rate)

• High Gravity (>1.065): 1.0-1.25 million cells/ml/°P

• Belgian/Wheat: 0.5-0.75 million cells/ml/°P

Factors Affecting Pitch Rate

• Wort Gravity: Higher gravity needs more yeast

• Beer Style: Lagers need more than ales

• Yeast Health: Older yeast needs higher pitch rate

• Fermentation Temperature: Lower temps need more yeast

Yeast Viability

Liquid Yeast Degradation

Yeast viability decreases over time:

• 1 month: 80-90% viable

• 2 months: 60-75% viable

• 3 months: 40-60% viable

• 4+ months: Consider a starter

PurePitch® Viability

Formula for White Labs PurePitch® packets:

Time	Viability
1 month	99.21%
2 months	98.05%
3 months	90.26%
4 months	84.28%
5 months	79.35%
6 months	71.59%

Dry Yeast

• Longer shelf life than liquid

• 2 years typical viability

• 10-20 billion cells/gram

• No starter needed usually

Making a Yeast Starter

Equipment Needed

• Flask: 2L or larger Erlenmeyer

• Stir Plate: Optimal for growth

• Stir Bar: Magnetic, sanitized

• DME: Dry malt extract

• Foil: To cover flask

Starter Preparation

1. Calculate DME Amount

   • 10:1 ratio (100g DME per liter)

   • Target 1.036-1.040 gravity

2. Boil and Cool

   • Boil water and DME 10 minutes

   • Cool to room temperature

   • Transfer to sanitized flask

3. Pitch Yeast

   • Add yeast to cooled wort

   • Cover with sanitized foil

   • Start stir plate

4. Growth Phase

   • 24-48 hours typical

   • Keep at room temperature

   • Constant stirring best

Stepping Up Starters

For very high cell counts, use the multi-step feature in the tool (up to 10 steps):

1. Make an initial starter (the tool calculates the optimal size)

2. After 24-48 hours, decant and step up to the next volume

3. Each subsequent step typically doubles the previous volume

4. The tool tracks the cumulative cell count through all steps

Decanting vs. Pitching All

Decanting (Recommended for lagers):

• Refrigerate starter overnight

• Pour off clear liquid

• Pitch concentrated yeast

Pitch Everything (Common for ales):

• Add entire starter to wort

• Accounts for volume in recipe

• Simpler process

Pitch Rate Guidelines

Underpitching Effects

• Longer lag time

• Stressed yeast

• Off-flavors (esters, phenols)

• Incomplete fermentation

• Diacetyl production

Overpitching Effects

• Less yeast character

• Reduced esters

• Faster fermentation

• Possible autolysis

• Generally less problematic

Style Considerations

Clean Beers (Lagers, Light Ales):

• Higher pitch rates

• Minimize yeast stress

• Clean fermentation

Character Beers (Belgian, Hefe):

• Lower pitch rates acceptable

• Encourage ester production

• More yeast expression

Dry Yeast Guidelines

Rehydration (Optional)

1. Boil water, cool to 35-40°C (95-105°F)

2. Sprinkle yeast on surface

3. Wait 15 minutes

4. Gently stir

5. Pitch when within 5°C (10°F) of wort

Direct Pitch

• Modern dry yeast works well

• Sprinkle on wort surface

• No need to rehydrate

• Follow manufacturer guidelines

Amount Needed

• Typical: 1 packet per 19 liters (5 gallons) up to 1.060

• High Gravity: 2+ packets

• Lagers: Double the ale amount

Troubleshooting

Slow Start

• Check viability calculation

• Verify pitch rate

• Consider temperature

• Oxygenation levels

Stuck Fermentation

• Likely underpitched

• Add fresh yeast

• Make small starter first

• Check temperature

Off-Flavors

• Review pitch rate

• Check yeast age

• Verify storage conditions

• Consider yeast health

Using with Your Recipes

• Calculate pitch rates based on your recipe's OG and volume

• The tool remembers your last settings

• Use results to plan yeast purchases and starters

• Track what pitch rates work best for your system

Tips

• Always calculate pitch rates, don't guess

• Use fresh yeast when possible

• Keep yeast refrigerated

• Aerate wort well before pitching

Related docs

• Recipe Designer

• Brewing Knowledge: Fermentation