Fermentation Time Calculator Formula

Understand the math behind the fermentation time calculator. Each variable explained with a worked example.

Use the Fermentation Time Calculator

Formulas Used

Minimum Fermentation Time

min_days = round(base_days * temp_factor * salt_factor * 0.7 * 10) / 10

Ideal Fermentation Time

ideal_days = round(base_days * temp_factor * salt_factor * 10) / 10

Maximum Fermentation Time

max_days = round(base_days * temp_factor * salt_factor * 1.5 * 10) / 10

Variables

VariableDescriptionDefault
ferment_typeFermentation Type1
temp_fAmbient Temperature(°F)70
salt_pctSalt % (weight of salt / weight of vegetables)(%)2.5
base_daysDerived value= (ferment_type == 1) * 21 + (ferment_type == 2) * 10 + (ferment_type == 3) * 0.5 + (ferment_type == 4) * 7calculated
temp_factorDerived value= 70 / temp_fcalculated
salt_factorDerived value= 1 + (salt_pct - 2.5) * 0.2calculated

How It Works

How Fermentation Time Is Estimated

Key Factors

  • Temperature: Warmer environments speed up fermentation. 65-75°F is ideal for most lacto-fermentation.
  • Salt: Higher salt slows fermentation. Standard sauerkraut uses 2-3% salt by weight.
  • Ferment type: Each type has a different base timeline.

    • Base Times (at 70°F, 2.5% salt)

  • Sauerkraut/Kimchi: 14-28 days
  • Kombucha: 7-14 days
  • Yogurt: 8-12 hours
  • Sourdough starter: 5-10 days to establish

    • Worked Example

    Estimate sauerkraut fermentation time at 70°F with 2.5% salt.

    ferment_type = 1temp_f = 70salt_pct = 2.5
    1. 01Base time for sauerkraut = 21 days.
    2. 02Temp factor = 70 / 70 = 1.
    3. 03Salt factor = 1 + (2.5 - 2.5) x 0.2 = 1.
    4. 04Ideal time = 21 x 1 x 1 = 21 days.
    5. 05Minimum = 21 x 0.7 = 14.7 days.
    6. 06Maximum = 21 x 1.5 = 31.5 days.

    Ready to run the numbers?

    Open Fermentation Time Calculator