New Technologies for Fermentation

CelloFuel Strategy - What do we do?

The world’s largest yeast companies, including LeSaffre (>$3B/yr), AB Mauri (>$2B/yr), Angel Yeast (>$1B/yr) and Lallemand (~$1B/yr), produce yeast that is too expensive to compete with soy protein for animal feed. We’re developing technologies for reducing the cost of producing yeast so that it competes with soy protein in fish feed and animal feed. Our solution is to use new technologies to significantly reduce the CAPEX and OPEX to produce yeast and to co-locate yeast production with the production of sugars (sugarcane mills, sugar beet plants, and deep grain processing plants).

Our focus is on innovative, cost-effective technologies for producing single-cell protein (yeast) for fish feed and animal feed at a lower cost than soy protein. Yeast is also a much healthier fish feed and animal feed than soy protein.

We are licensing these patents, technologies and reference designs to customers who want to produce yeast at an industrial scale. Our target markets are located worldwide, particularly in the USA, Brazil, Russia, India and China.

Our key patent is a bacterial contamination control technique involving limiting nickel in the fermentation broth while using only urea as the nitrogen source for yeast. Bacteria can’t use urea as a nitrogen source without nickel as a cofactor, thus preventing bacterial growth by limiting nickel. Yeast only needs biotin and doesn’t need nickel to use urea as a nitrogen source. Using this patent makes it possible to eliminate the sulfuric acid wash in Brazilian sugarcane ethanol plants and makes it possible to use evaporative cooling to reduce the cost of producing yeast.

Our key reference design for making yeast is a containerized fermenter using multiple plastic IBC totes which don’t leach nickel like stainless steel does. This reference design uses flocculating yeast instead of centrifugation and uses evaporative spray cooling instead of plate heat exchangers. This design allows unattended operation for months at a time because there’s no need to maintain centrifuges and clean plate heat exchangers. Since there’s no bacterial contamination, a simple spray of boiling water is used for CIP (clean in place) instead of a harsh caustic wash for sterilization.

These containerized fermenters use standard 20 ft and 40 ft shipping containers. They are designed for stacking 8 high when operating, transporting by train or truck, and rapidly constructing into large systems.

A Look Into the Future:

We asked Grok AI this question:

“As demand for sugar decreases due to health concerns worldwide, and if the demand for fuel ethanol remains constant, what other profitable products can be produced from sugarcane juice?“

Answer:

“Another lucrative product is yeast, which can be cultivated using sugarcane juice as a substrate. Yeast has steady demand across multiple industries, including baking, brewing, and nutritional supplements. Typically produced from molasses (a byproduct of sugar refining), yeast production could shift to sugarcane juice directly, especially as sugar production declines. This adaptability, combined with a well-established market, makes yeast a reliable and profitable option for diversifying revenue from sugarcane juice.”

Contamination Control

Bacterial contamination is often the biggest technical problem when fermenting ethanol or growing yeasts at an industrial scale.

We’ve invented a patented technology for preventing contamination by using urea as the sole nitrogen source along with ensuring that the nickel concentration is less than 1 mg/kg. No acid wash or antibiotics are needed to prevent 100% of all bacterial contamination.

We are also using fed-batch feeding of both urea and sugars, supplemented with biotin, along with recycling yeast, which results in a very high fermentation rate with no bacterial contamination.

This technique allows fermentation at pH 4 to pH 7 without bacterial contamination.

Brazil Patent BR112024003499

PCT Patent WO2024092285A2

U.S. Patent No. 12,297,423

U.S. Patent App. No. 19/202,827, filed May 8, 2025

Low-Cost Fermenter

We are building a low-cost fermenter that takes advantage of our contamination control patents.

This low-cost fermenter is designed for fermentation of sugars to produce yeast.

The building block for a large-scale fermenter is the 1 m3 Intermediate Bulk Carrier (IBC). This enables us to build large, containerized, stackable fermenters for less than $500/m3, while traditional fermenters cost more than $15,000/m3. The operating cost of our low-cost fermenters is also much lower than traditional submerged fermentation.

These low-cost fermenters don’t use centrifuges to recycle yeast but instead use sedimentation of flocculating yeast strains such as Lallemand Lalvin EC-1118. This is efficient because the settling distance is less than 1 m.

These low-cost fermenters don’t use heat exchangers to remove the heat of fermentation, but instead use evaporative cooling , which reduces CAPEX and OPEX as well as eliminating the expense of cleaning plate heat exchangers.

These low-cost fermenters are containerized and are fully automated.

U.S. Patent App. No. 19/202,827, filed May 8, 2025

Healthier than Soy Protein

Our low-cost fermenter produces yeast that is significantly healthier than soy protein, at a competitive price.

Growing soybeans uses many unhealthy herbicides and pesticides, and these enter the food chain through soy protein in animal feed.

Soy also contains many anti-nutritional compounds that are unhealthy in fish feed and animal feed.

Yeast has been shown to be much healthier than soy protein and has a better balance of amino acids than soy protein. It is also more sustainable, needing less land than soybeans.

Our low-cost fermenter can produce yeast which has been shown to be very nutritious for fish and chicken, and thus makes a more valuable feed for fish and chicken.

The base price of dried fodder yeast varies by country, with higher-cost economies like Japan and the U.S. at the top end.

The reduced CAPEX and OPEX of our low-cost fermenter along with producing a more nutritious animal feed than soy protein results in a cost-effective product.

Yeast from Sugars

Our low-cost fermenter can cost-effectively produce protein-rich yeast from many sugar solutions. These sugars include raw sugar, VHP sugar, hydrolyzed dry-grind grain, sugar beet juice, sugar beet molasses, sugarcane juice, sugarcane molasses and sweet sorghum juice.

Molasses from sugarcane and sugar beet are generally the lowest cost sugars to use to produce yeast, but other sugars are also cost-effective, especially when factoring in the cost of disposal of the vinasse/supernatant.

Molasses is produced in large quantities worldwide, can be stored without spoiling for year-round production of yeast and is cost-effective to transport.

When using these sugars to grow yeast, sometimes 20-30% of vinasse can be reused in each fermentation cycle. The resulting vinasse can generally be used to fertilize crops.

The energy cost of spray-drying yeast cream to dried inactive yeast significantly adds to the cost of spray-dried yeast.

Spray-dried yeast is cost-effectively produced in sugarcane mills in Brazil, India and Thailand by using the excess heat from bagasse combustion for spray-drying. It’s also cost-effectively produced in Russia with natural gas ($0.11/kg to spray-dry yeast), in China with low-cost energy ($0.29/kg to spray-dry yeast) and in the USA with natural gas ($0.52/kg to spray-dry yeast)

S. cerevisiae yeast is Generally Recognized As Safe (GRAS) and is approved worldwide for human consumption, fish feed and animal feed.

Using Yeast in Animal Feed

Yeast is very healthy when consumed by fish, chicken, pigs and humans. The feed conversion ratio (how many kg of feed it takes per kg of weight gain) is between 1.0 and 2.0 for fish, between 1.7 and 2.0 for chicken, between 2.5 and 3.5 for pigs and between 6.0 and 10.0 for cattle (so feeding yeast to cattle isn’t very efficient).

About 140 million tons of chicken (poultry) are raised per year, 110 million tons of pigs are raised per year, and 90 million tons of fish are raised in aquaculture per year, so the market for yeast in fish feed and animal feed is very large. The size of the worldwide market for nutritional yeast for human consumption is estimated at less than 10,000 tons per year.

There are two important aspects of the health effects of yeast in fish feed and animal feed - whether it provides essential amino acids for fish and animal growth and whether there is a good balance of essential fatty acids in fish and animals.

Essential Amino Acids

Essential amino acids are amino acids that fish, chicken, pigs and humans cannot synthesize on their own and must be obtained through the diet. There are nine essential amino acids:

  1. Histidine - Supports growth, tissue repair, and histamine production.

  2. Isoleucine - Aids in muscle metabolism, energy regulation, and hemoglobin production.

  3. Leucine - Promotes muscle protein synthesis and tissue repair.

  4. Lysine - Involved in protein synthesis, hormone function, and enzyme production.

  5. Methionine - Supports detoxification, metabolism, and sulfur-containing compound production.

  6. Phenylalanine - Precursor for neurotransmitters like tyrosine, dopamine, and norepinephrine.

  7. Threonine - Essential for collagen, elastin, and immune function.

  8. Tryptophan - Precursor for serotonin and melatonin, aiding mood and sleep regulation.

  9. Valine - Supports muscle growth, energy production, and tissue repair.

Arginine is also an essential amino acid in animal feed for fish, chicken and pigs.

Yeast is complete in all essential amino acids and also provides all B-vitamins (except for vitamin B12). Depending on the growth environment, yeast can be deficient in methionine and/or lysine and sometimes needs to be supplemented in fish, chicken, pig and human diets.

Synthetic amino acids (e.g., L-lysine, DL-methionine, L-threonine) are commonly added to diets containing S. cerevisiae to correct deficiencies, especially in chicken and pigs. This is economically viable and reduces reliance on traditional protein sources like fishmeal or soybean meal.

Soy protein is also deficient in methionine and lysine and provides fewer B-vitamins than yeast.

Essential Fatty Acids

Essential fatty acids are fats that the human body cannot produce and must be consumed through food. There are two essential fatty acids:

  1. Alpha-Linolenic Acid (ALA) - An omega-3 fatty acid, crucial for heart health, brain function, and reducing inflammation. Found in flaxseeds, chia seeds, walnuts, hemp seeds, and certain oils (e.g., flaxseed oil).

  2. Linoleic Acid (LA) - An omega-6 fatty acid, important for skin and hair health, growth, and cell membrane function. Found in vegetable oils (e.g., sunflower, safflower, corn), nuts, seeds, and processed foods.

The human body uses ALA and LA as precursors to synthesize other fatty acids, like EPA and DHA (omega-3s), though conversion is limited. A balanced intake of omega-3 and omega-6 fatty acids is important to avoid inflammation from excessive omega-6 consumption.

Yeast does not provide either of these essential fatty acids so it must be provided in the human diet. Omega-6 fatty acids are far too high in existing human diets worldwide. Omega-3 fatty acids can be enhanced in fish by adding flaxseed oil to fish feed and can be enhanced in chicken and pigs (and especially chicken eggs) by adding flaxseed and flaxseed oil to chicken feed and pig feed.

Fish, chickens and pigs can synthesize ALA and LA from their diet and can also synthesize EPA and DHA which enhances EPA and DHA when consumed by humans.

Soy protein has a large excess of omega-6 fatty acids, is deficient in omega-3 fatty acids and contains no EPA or DHA. Soy protein in fish feed and animal feed results in fish and animals with too much omega-6 fatty acid content, which is ultimately unhealthy for humans. Feeding fish and animals yeast and flaxseed/flaxseed oil results in a much healthier diet of fish, chicken and pork.

Anti-Nutritional Factors (ANFs) in Soy Protein

Soy protein contains many anti-nutritional compounds that are unhealthy in the diet of fish and animals. This includes trypsin inhibitors, lectins, oligosaccharides, phytic acid, saponins, soy antigens, isoflavones and tannins.

Carnivorous fish (e.g., salmonids, shrimp) are particularly sensitive to soy ANFs due to their limited ability to digest plant-based carbohydrates and their sensitive gastrointestinal systems. High soy inclusion (e.g., >30% soybean meal) often leads to enteritis, reduced growth, and altered gut microbiota.

Young monogastric animals (piglets, chicks, calves) are most affected due to immature digestive systems. For example, galacto-oligosaccharides and trypsin inhibitors are critical for piglets, while antigens and lectins are problematic for calves. Poultry are sensitive to trypsin inhibitors and oligosaccharides, leading to diarrhea and reduced growth.

Yeast does not contain any of these anti-nutritional factors and results in healthier fish, chickens and pigs when yeast is included in their feed.

Target Markets

Our target markets are where there are low-cost sugars for making yeast, low-cost energy for spray drying, and a large market for fish feed and/or animal feed.

United States: The United States has low-cost sugars from dry-grind corn, low-cost energy from natural gas for spray-drying yeast and a large market for animal feed.

Brazil: Brazil has low-cost sugars from sugarcane, low-cost energy from burning bagasse for spray-drying yeast and a large market for fish feed and animal feed.

Russia: Russia has low-cost sugars from sugar beet, low-cost energy from natural gas for spray drying yeast and a large market for fish feed and animal feed.

India: India has low-cost sugars from sugarcane, low-cost energy from burning bagasse for spray-drying yeast and a large market for fish feed and animal feed.

China: China produces a large amount of many crops that can be used to produce sugars, has low-cost energy for spray-drying yeast and a large market for fish feed and animal feed.

Design Goals and Design Decisions

Since feedstock costs and capital costs are the major contributors to the cost of making yeast, the main design decision is what feedstocks to use. We’re not using methane as a feedstock, since the capital costs of U-loop fermenters are extremely high and explosion-proofing is costly. We’re not using lignocellulosic feedstocks since the cost of gathering, transporting and hydrolyzing the feedstocks make the cost of these plants uneconomical. We’re not using methanol or raw glycerol as a feedstock since regulatory approval is expensive and time-consuming and since Pichia pastoris (Komagataella pastoris) isn’t a flocculating yeast (see below). This is why we’re focused on feedstocks that can produce sugar streams of glucose, fructose and sucrose.

An under-appreciated fact is that many crops that can produce sugar streams have a limited harvest season and plants that process these crops to produce ethanol or yeast can’t operate year-round. Our goal is to produce flex plants that produce ethanol and/or yeast year-round, albeit with different crops. For instance, a flex plant can use sugarcane and sweet sorghum for part of the year and use corn and wheat for other parts of the year. This makes a flex plant use capital more efficiently than a single-crop plant.

We’ve focused on minimizing capital costs since this is a significant contributor to the cost of yeast at a million-ton scale. We’re focused on a common containerized fermenter design that produces yeast from sugar streams containing more than 150 g/L of glucose, sucrose and fructose. These sugar streams are currently produced from sugarcane, sugar beet, sweet sorghum, wheat and corn.

To minimize the cost of capital per ton of product per year, we’re minimizing the capital cost per cubic meter of fermenter and maximizing the product produced per year per cubic meter of fermenter. To minimize the cost of capital we use a design that doesn’t require plate heat exchangers, doesn’t require centrifuges and that can be built from mass-produced components (shipping containers and IBC totes). To maximize the product produced per year we use yeast recycling without an acid wash (no lag time at beginning of fermentation cycle) and without sterilizing after each batch (minimizing time between fermentation cycles). This takes advantage of our patented contamination control technique.

To minimize the operating cost per ton of product, we’re using evaporative cooling to remove fermentation heat (reducing energy costs and eliminating the cost of cleaning plate heat exchangers), using yeast sedimentation to harvest yeast (eliminating the operating cost of centrifuges) and using automated operations with no manual intervention for each fermentation cycle (reducing cost of skilled personnel).

A critical part of capital cost reduction and operating cost reduction is to use sedimentation instead of centrifugation to separate yeast from the fermentation broth. This requires the use of a flocculating yeast that sediments rapidly at the end of a fermentation cycle. This eliminates the possibility of using Candida utilis and Pichia pastoris, since these yeasts don’t flocculate and sediment. We’re using 1 cubic meter IBC totes as a fermentation module because the sedimentation time over a 1 m height is at least 8 times faster than the sedimentation time over the 8 m height of a typical fermenter.

This flocculating yeast needs to be a flocculating yeast that sediments rapidly, needs to be approved as a component of fish feed and animal feed, and needs to out-compete wild yeasts. We’re using a Saccharomyces cerevisiae yeast strain that’s distributed worldwide - Lallemand Lalvin EC-1118. The sedimentation rate is very high. It grows at temperatures up to 30 C, has very high rate of growth, produces very little foam, and is approved worldwide as a component of fish feed and animal feed. It also out-competes wild yeasts, both because it has a higher growth rate than wild yeasts and because it secretes a “competitive killer factor” (proteins or glycoproteins (toxins) that are lethal to sensitive yeast strains but do not affect EC-1118).

Our Flex Plant Design for Brazil

Flex plants are versatile facilities capable of producing sugar solutions from a wide range of feedstocks and converting those solutions into various products. This adaptability allows them to respond effectively to changing market conditions and feedstock availability. In contrast, traditional ethanol plants, such as corn ethanol plants, are typically limited to a single feedstock. These conventional plants face inefficiencies when attempting to incorporate alternative feedstocks like sugarcane or sweet sorghum, primarily due to their lack of yeast recycling systems, which are essential for more efficient fermentation processes.

The world’s most efficient ethanol production is achieved through Brazilian-style fermenters, which employ yeast recycling in 12-hour cycles to maximize throughput. Our flex plant design integrates processes that generate sugar solutions from diverse feedstocks—such as sugarcane, sweet sorghum, sugar beets, corn, wheat, rice, and cassava—that are specifically tailored for use in these Brazilian-style fermenters. This ensures the efficient production of ethanol using these advanced systems.

This design of a flex plant allows much higher throughput by overlapping producing the sugar solution with fermenting the sugar solution to produce ethanol and/or yeast. Modern high-temperature enzymes make it possible to produce sugar solutions from grain in the same 12-hour cycle as Brazilian-style fermenters, overlapping these two processes. Using alpha-amylase enzymes at 90°C and glucoamylase enzymes at 65°C is more than 8 times faster than the old-fashioned process in U.S. corn ethanol plants using expensive jet cookers with alpha-amylase enzymes to liquefy followed by many days of using glucoamylase enzymes to simultaneously saccharify and ferment (SSF) at 32°C.

This design enables a flex plant to switch between different feedstocks throughout the year based on their availability and cost. Moreover, the plant can produce a variety of products, including ethanol and yeast, allowing it to adapt to market demands effectively.

Improved Contamination Control in Brazilian Sugarcane Ethanol Plants

We have developed technologies for cost-effective control of bacterial contamination during large-scale yeast fermentation (both aerobic and anaerobic). Instead of adding anti-bacterial substances to a fermenter or using sulfuric acid washes to kill bacteria during yeast recycling, we eliminate nickel leaching and use urea as the sole nitrogen source. Bacteria can’t grow on urea without nickel as a co-factor, but yeasts only need biotin to grow on urea.

This technique allows fermentation without requiring aseptic conditions and is thus much less expensive than traditional fermentation techniques.

Example use in Brazil:

This technique can be used in sugarcane ethanol plants in Brazil to improve efficiency, produce more ethanol, reduce foaming and reduce the strong odor from the vinasse. The changes using this contamination control technique enable using yeast recycling without acid washing to speed up fermentation time in flex plants.

Changes required: Minimal changes are needed to integrate our contamination control technique:

  1. Use urea as the only nitrogen source, replacing ammonium sulfate

  2. Use fed-batch feeding of urea

  3. Make sure heat exchangers use stainless steel grade 316 (not grade 304)

  4. Don’t use acid wash, recycle yeast cream directly from centrifuge

  5. Clean vats with high pressure water spray, without caustic

Benefits:

  1. Reduces wild yeast contamination: Without bacterial contamination, contamination by D. bruxellensis and other wild yeasts doesn’t occur when using a fast-growing S. cerevisiae strain like PE-2.

  2. Reduces foaming: Foaming is reduced because the extracellular protein from Lactobacillus is eliminated.

  3. Reduces strong odors: Eliminating sulfur from the wash and changing ammonium sulfate to urea results in significant reduction of sulfur in the vinasse, which reduces the strong odor from bacteria producing hydrogen sulfide from the vinasse. Not using sulfur dioxide in sugarcane juice clarification can further reduce the strong odor from the vinasse.

  4. Reduces distillation column fouling: Eliminating the sulfuric acid wash eliminates adding soluble calcium sulfate to the distillation columns when recovering ethanol from this wash. Calcium sulfate from the wash also precipitates in the distillation column, causing fouling and requiring more cleaning.

  5. Improves distillation efficiency: Sulfuric acid wash water dilutes the mash being distilled, which increases the energy and time needed for distillation. It’s more efficient to carry this ethanol with the recycled yeast into the next fermentation cycle.

  6. Increases profits: The cost savings are considerable due to reducing the time per batch by 2-4 hours and improving process efficiency. The increase in income for a typical Brazilian sugarcane ethanol plant producing 6% more ethanol (12 million liters) due to eliminating bacterial contamination in fermenters is approximately $6,000,000 per year, assuming an ethanol price of $0.50 per liter. This figure could range from $3.6 million to $8.4 million depending on ethanol prices or plant size. The cost savings from eliminating the sulfuric acid wash is about $500,000 per year. The cost savings from eliminating calcium sulfate from the distillation columns is about $1.3 million per year. The cost savings from reducing the batch cycle time from 12-15 hours to 10-12 hours is about $1.3 million per year. The total cost savings are about $10,000,000 per year for a large sugarcane ethanol plant.

  7. Future: Sugarcane ethanol fermenters and distillation columns are often idle when it’s more profitable to make sugar than ethanol. If the fermenters and distillation columns could produce ethanol from corn and wheat at the same rate as from sugarcane, it would increase Brazil’s production of ethanol by 25% to 50%. In Brazil, this would use 21 million metric tons of corn from the 47 million tons of corn that Brazil exports every year. Similarly, these kinds of flex plants could be built in the U.S., Russia, India and China. This technique for making flex plants that take advantage of our contamination control patent has been submitted as U.S. Patent App. No. 19/202,827 and we will soon submit this patent in Brazil, Russia, China and India.

The Fermentation Cycle in Brazilian Sugarcane Ethanol Production

In Brazil, sugarcane ethanol production typically employs the Melle-Boinot process, a fed-batch fermentation process, which is widely used due to its efficiency and scalability. The process begins with the preparation of a substrate, usually sugarcane juice or molasses, derived from sugarcane processing. This substrate, rich in fermentable sugars like sucrose, glucose, and fructose, is fed into large fermentation vats. The fermentation is carried out by the yeast Saccharomyces cerevisiae, a robust strain well-suited for ethanol production.

  • Fermentation Phase: The yeast ferments the sugars into ethanol and carbon dioxide over a period typically ranging from 6 to 12 hours, depending on factors like temperature (maintained around 30–34°C), sugar concentration, and yeast activity. The process is "fed-batch," meaning the substrate is added incrementally to avoid overwhelming the yeast with high sugar levels, which could inhibit fermentation.

  • Harvesting Phase: Once fermentation is complete, the fermented broth (containing ethanol, yeast, water, and residual sugars) is centrifuged. This separates the liquid fraction (called "wine," containing ethanol) from the yeast biomass. The ethanol-rich liquid proceeds to distillation to purify and concentrate the ethanol, while the yeast is collected for reuse.

  • Yeast Recycling: In the standard process, approximately 90–95% of the centrifuged yeast is recycled to the next fermentation cycle to maintain high productivity and reduce costs. Before recycling, the yeast is often subjected to an acid wash (using sulfuric acid) or a water wash to remove contaminants, particularly bacteria, and to refresh the yeast by reducing the buildup of fermentation byproducts and dead cells.

  • Vat Cleaning: After each cycle, the fermentation vats are cleaned to remove residues and prevent contamination in the next batch. This cleaning typically involves caustic soda (sodium hydroxide), often heated, to ensure thorough sanitation, followed by rinsing.

This cycle repeats multiple times, leveraging the recycled yeast to maximize efficiency in Brazil’s large-scale ethanol industry, which produces billions of liters annually.

Improvements with No Bacterial Contamination and No Yeast Washing

Now, let’s consider a modified process where no bacterial contamination occurs during fermentation, and no acid or water wash is applied to the centrifuged yeast. Instead, 95% of the yeast is recycled directly without washing. Here’s how this alters and potentially improves the process:

Operational Improvements

  1. Elimination of Ethanol Recovery from Acid Wash:

    • In the standard process, acid washing the yeast can dilute any residual ethanol clinging to the yeast biomass. This ethanol must be recovered (e.g., via distillation), adding an energy-intensive step. By skipping the wash, no ethanol is lost to a wash solution, eliminating this recovery process and saving energy.

  2. No Acid Neutralization:

    • Acid washing requires neutralizing the acidic yeast slurry (e.g., with a base like lime) before recycling to avoid harming the yeast or altering the fermentation pH. Skipping the wash eliminates the need for neutralization, reducing chemical inputs, waste treatment, and associated costs.

  3. Simplified Process:

    • Removing the washing step streamlines operations by reducing the number of unit processes, lowering labor, equipment maintenance, and water usage.

These changes enhance plant efficiency by cutting energy, chemical, and operational expenses.

Equilibrium Concentration of Metabolites and Dead Cells

Without washing, the recycled yeast carries over fermentation metabolites (e.g., organic acids like acetic acid, glycerol, and higher alcohols) and weak or dead yeast cells into each new cycle. Here’s how this stabilizes:

  • Accumulation: Initially, the concentrations of these components increase with each cycle as 95% of the yeast, including its metabolites and dead cells, is reused.

  • Removal and Dilution:

    • 5% Yeast Loss: The 5% of yeast not recycled (discarded or lost) removes a small fraction of these components from the system.

    • Fresh Substrate Addition: Each cycle introduces fresh sugarcane juice or molasses, diluting the metabolite concentration in the fermentation broth.

  • Equilibrium: Over multiple cycles, an equilibrium concentration is reached where the rate of metabolite production and dead cell accumulation equals their removal (via the 5% yeast loss) and dilution (via fresh substrate). This equilibrium level would be higher than in a washed-yeast system, where washing removes some metabolites and dead cells each cycle. However, since Saccharomyces cerevisiae is tolerant to many of its own byproducts (up to certain thresholds), and no bacterial competition exists, this higher concentration is manageable without significantly impairing fermentation efficiency.

Quantitatively, this equilibrium depends on fermentation conditions (e.g., sugar concentration, cycle duration), but qualitatively, it stabilizes at a level reflecting the balance of production, loss, and dilution.

Cycle Time Improvement with Water-Washed Vats

Finally, consider how not washing the yeast improves the overall cycle time when fermentation vats are cleaned with water instead of caustic:

  • Standard Cycle Time Components:

    • Fermentation: 6–12 hours.

    • Harvesting (centrifugation): ~1–2 hours.

    • Yeast Washing: In the standard process, acid or water washing, neutralization, and rinsing add 1–2 hours (depending on scale and method).

    • Vat Cleaning: Caustic cleaning, often heated and followed by rinsing, takes 2–3 hours or more.

  • Modified Process:

    • No Yeast Washing: Eliminating the washing step saves 1–2 hours per cycle. After centrifugation, the yeast is immediately recycled, cutting a significant preparation step.

    • Water-Washed Vats: Cleaning vats with water instead of caustic is faster—potentially reducing cleaning time to 1–2 hours—since it avoids heating, prolonged chemical exposure, and extensive rinsing. Water suffices here because bacterial contamination is absent, and the goal is simply to remove physical residues (yeast, sugars) rather than sanitize deeply.

  • Combined Effect: Without yeast washing, the time between fermentation cycles shrinks directly. Pairing this with quicker water-based vat cleaning further shortens the downtime, allowing cycles to restart sooner. For example, a cycle that took 12–15 hours (fermentation + harvesting + washing + caustic cleaning) could drop to 10–12 hours, boosting throughput.

The absence of bacterial contamination enables these simplifications without risking fermentation performance, as bacteria—typically controlled by acid washing and caustic cleaning—are not a factor.

Conclusion

In Brazilian sugarcane ethanol production, the standard fed-batch fermentation cycle involves fermenting sugarcane juice or molasses with Saccharomyces cerevisiae, followed by centrifugation, yeast washing, and vat cleaning with caustic. When no bacterial contamination occurs and 95% of the centrifuged yeast is recycled without washing:

  • Plant operations improve by eliminating ethanol recovery and acid neutralization, saving energy, chemicals, and time.

  • Metabolite and dead cell concentrations reach a higher but stable equilibrium, balanced by yeast loss and substrate dilution, tolerable due to no bacterial interference.

  • Cycle time shortens by removing the yeast washing step (1–2 hours saved) and, when vats are water-washed instead of caustic-cleaned, further reducing cleaning time (1–2 hours vs. 2–3+ hours), enhancing overall efficiency.

This optimized process leverages the absence of contamination to simplify and accelerate ethanol production.

Reduces fermentation time:

In the improved process, fermentation time is reduced because the yeast is no longer subjected to the stress of acid washing. Here’s how this works:

Acid Washing in Traditional Processes

In traditional ethanol production, yeast is often recycled between fermentation cycles to maximize efficiency. To control bacterial contamination during this recycling, the yeast is washed with sulfuric acid. However, this acid exposure stresses the yeast cells. The stress can damage their cell membranes, lower their viability, and slow their metabolic activity. When these stressed yeast cells are reused, they need time to recover before they can ferment sugars efficiently. This recovery period, or lag phase, extends the overall fermentation time.

Eliminating Acid Washing in the Improved Process

In the improved process, the acid washing step is skipped entirely. After fermentation, 95% of the yeast is separated using centrifugation and directly reused in the next cycle without being exposed to acid. Since there’s no acid wash, the yeast avoids this stress. As a result:

  • Higher Viability: The yeast cells remain healthier, with intact membranes and better metabolic function.

  • No Recovery Time: Without the need to recover from acid stress, the yeast can start fermenting the new batch of sugarcane juice or molasses immediately.

How This Reduces Fermentation Time

The key to shorter fermentation time lies in the yeast’s improved condition:

  • Faster Start: In the traditional process, acid-washed yeast may enter a lag phase as it recovers from stress, delaying the start of active fermentation. In the improved process, this lag phase is minimized or eliminated because the yeast is unstressed and ready to work right away.

  • More Efficient Fermentation: Healthier yeast converts sugars into ethanol and carbon dioxide more quickly. Without the burden of repairing acid-induced damage, the yeast ferments at a faster rate, completing the cycle sooner.

How Much Time Is Saved?

The exact reduction in fermentation time depends on factors like the yeast strain, sugar concentration, and fermentation conditions. However, by avoiding acid stress, fermentation could be shortened by approximately 10–20%. For a typical 8–12 hour fermentation cycle, this might mean a savings of 1–2 hours per batch.

Additional Advantages

Beyond reducing fermentation time, skipping acid washing simplifies the process. It eliminates the need for acid, neutralizing agents, and extra steps like treating the wash, which also saves time and resources. With faster fermentation cycles, the plant can process more batches in the same timeframe, increasing overall productivity.

Conclusion

By eliminating acid washing, the improved process keeps the yeast healthier and more active, avoiding the stress that slows fermentation in the traditional method. This leads to a quicker start and more efficient sugar conversion, ultimately reducing the fermentation time while improving the process’s simplicity and efficiency.

Who are we?

Hamrick Engineering was founded in 2013 by Edward B. Hamrick.

Edward (Ed) Hamrick graduated with honors from the California Institute of Technology (CalTech) with a degree in Engineering and Applied Science. He worked for three years at NASA/JPL on the International Ultraviolet Explorer and Voyager projects and worked for ten years at Boeing as a Senior Systems Engineer and Engineering Manager. Subsequently, Ed worked for five years at Convex Computer Corporation as a Systems Engineer and Systems Engineering Manager. Ed has been a successful entrepreneur for the past 25 years.

Alex Ablaev, MBA, PhD is Sr. Worldwide Business Developer. Alex previously worked for Genencor's enzymatic hydrolysis division, and is the President of the Russian Biofuels Association as well as General Manager of NanoTaiga, a company in Russia using CelloFuel technologies in Russia.

Alan Pryce, CEng is Chief Engineer. Alan is an experienced professional mechanical engineer - Chartered Engineer (CEng) – Member of the Institute of Mechanical Engineers (IMechE) - with 10+ years’ experience in the mechanical design and project management of factory automation projects in UK and European factories. He has been a Senior Design Consultant and project manager for over 30 years working for Frazer-Nash Consultancy Ltd involved with many design and build contracts in the military, rail, manufacturing, and nuclear industries.

Maria Kharina, PhD, is Sr. Microbiology Scientist. Maria has a PhD in Biotechnology and is a researcher with 10+ years of experience. Maria was a Fulbright Scholar in the USA from 2016-2017.

Beverley Nash is Director of Marketing. Beverley has run Nash Marketing for over 30 years and has extensive experience in marketing planning and development for both new and established businesses. Beverley has worked for many global corporations in the technical marketplace and has been responsible for both the planning and management of many programs dealing with all aspects of company and product growth.

Dr. Ryan P. O'Connor (www.oconnor-company.com) provides intellectual property strategy consulting and patent prosecution. Dr. O'Connor holds a degree in Chemical Engineering from University of Notre Dame and a Ph.D. in Chemical Engineering from University of Minnesota. He has filed more than 1000 U.S. and PCT applications and is admitted to the Patent Bar, United States Patent & Trademark Office.

Hamrick Engineering Patent Portfolio