turning wood into yeast

Introduction to Food Yeast Production

  • Food Yeast: High in protein (50%), fats (2-7%), and vitamins, derived from wood carbohydrates and inorganic salts.

  • Yield: 40-50% carbohydrate conversion to yeast; better conversion than animal feed (20:1 for pigs).

  • Historical Context: Limited experimentation in the U.S. prior to 1943; German development of food yeast industry during protein shortages of WWII.

Production Processes of Food Yeast in Germany

Key Hydrolysis Methods

  • Sources for Yeast: Mainly from sugars derived through wood hydrolysis, including:

    • Complete hydrolysis via Scholler or Bergius processes.

    • Byproducts from sulfite pulping of wood.

  • Production Capacity:

    • Five plants post-WWII producing ~9,000 tons/year.

    • Hydrolysate yield: 200-400 lbs yeast per ton of wood.

Yeast Propagation

Preferred Organisms

  • Primary: Torula utilis strain; other strains include Torula pulcherima, Monilia candida, and Candida arborea.

  • Acclimatization: Most strains require adaptation to wood sugars.

Propagator Designs

  1. Vogelbush Propagator: Discontinuous, external tubes to manage foam via air circulation.

  2. Waldhof Continuous Propagator: Center draft tube for mixing; allows for maximum foaming to enhance aeration.

  • Benefit: Continuous operation maintains yeast in vigorous condition and reduces contamination.

Research at U.S. Forest Products Laboratory

  • Historical Research: Support for alcohol production from wood waste; investigations resumed during WWII.

  • Yeast Growth Studies: Initial sugar solutions neutralized, nutrients added (sodium sulfite for 0.05% concentration), and balanced for maximum yield.

Hydrolysis of Wood for Sugar Production

  • Improved Hydrolysis: Pumping 0.5% sulfuric acid through wood at controlled temperatures, yielding ~50% fermentable sugars.

  • Sugars Composition: Combination of pentoses and hexoses, with specification of yields depending on wood species.

Specific Production Methods

Waste Liquor from Sulfite Process

  • Yields 50% dry wood substance; sugars reach 65% fermentable.

Pre-Hydrolysis Techniques

  • Utilizes acid and steam pressure to extract hemicellulose and maximize fermentable sugars.

Challenges in Yeast Production

  • High foaming tendencies complicate fermentation; specific designs and additives developed for control.

  • Energy and water requirements documented for both batch and continuous operations.

Nutrient Requirements and Optimization

Key Nutrients

  • Nitrogen: Must be monitored; critical for optimal yeast yield (3.4 lbs per 100 lbs sugar recommended).

  • Phosphates and Potassium: Essential conditions established to ensure maximum sugar utilization.

Economic Considerations

  • Current cost estimates for yeast production from wood sugars under development; initial calculations suggest low-cost potential due to byproduct use.

Summary of Findings

  • Food yeast production from wood materials offers significant protein and vitamin supply potential.

  • Exploiting wood and byproduct sugars can reduce waste and contribute positively to food security.

  • Optimal conditions for fermentation rely on thorough understanding of species-specific characteristics and nutrient needs.