3. gas solubality : infulencial factors to actual air/ o2 flow rate and knowelge check

Factors Influencing Solubility of Oxygen in wort

  • Pressure

    • Directly proportional to solubility.

    • As pressure increases, solubility increases.

  • Temperature

    • Inversely proportional to solubility.

    • As temperature decreases, solubility increases.

  • Size of Gas Bubbles

    • Inversely proportional to solubility.

    • Smaller bubbles result in faster gas solubility.

  • Wort Gravity

    • Inversely proportional to solubility.

    • As the original gravity of the wort increases, gas solubility decreases.

Aeration Stage Adjustments

  • Adjustments may be needed at aeration to manage solubility variabilities.

  • Control the quality of gas:

    • Must be clean to avoid affecting flavor, aroma, foam, haze, etc.

    • Must be dry to reduce microbiological contamination.

      • Common methods: Refrigeration, desiccants, or a combination.

    • Ensure sterility using in-line membrane filters or UV light.

Control of Gas Quantity

  • Precise control of the quantity of oxygen added to wort is necessary.

  • Methods:

    • Automated systems measure dissolved oxygen and provide feedback to incoming gas meter.

    • Simple ball float gas meters can be used.

  • Use fine aerators to create small bubbles for maximum solubility.

  • Pipeline design should create a Venturi effect to aid in mixing and solubility.

  • Allow sufficient pipeline length for gas to solubilize before yeast pitching to prevent toxic effects of pure oxygen on yeast.

Temperature Effects on Oxygen Solubility

  • Temperature influence on gas solubility highlighted:

    • A difference of one degree Celsius can lead to a near 5% change in dissolved oxygen concentration.

    • A five-degree difference can result in almost a 15% change.

      • Importance of maintaining low temperatures during aeration to achieve desired DO levels.

Theoretical Flow Rate Calculation

  • Formula used to calculate theoretical flow rate for aeration:

    • Based on wort volume, target dissolved oxygen, and transfer time from whirlpool to fermenter.

    • The 0.35 factor indicates liters of air needed per hectoliter of wort for one part per million dissolved oxygen.

  • Air versus pure oxygen:

    • Air (20% oxygen): Requires five times the volume to achieve the same dissolved oxygen levels compared to pure oxygen.

    • Excessive foaming can be an issue with air usage.

Practical Considerations for Gas Usage

  • Theoretical formulas must be adjusted for actual flow rates due to solubility being less than 100%.

  • Actual requirements are often two to three times more than theoretical calculations.

  • Common challenges:

    • Uneven gas bubble distribution.

    • Non-dissolved bubbles and foaming during filling lead to gas loss.

    • Flotation tanks can remove gas due to their reliance on foaming for particle removal, leading to increased gas flow rates.

Final Thoughts

  • Ensure gas is dry to minimize risks of contamination, while clean and sterile gas is essential.

  • Understand and control temperature impacts on oxygen solubility to achieve optimal fermentation conditions.