CREMER: Crude glycerol could cut fermentation costs, but cheaper does not always mean better

FermBase by CREMER and CREMER OLEO have published a new white paper examining glycerol as a renewable carbon source for industrial fermentation, with growing biodiesel production creating larger volumes of a by-product that could offer an alternative to glucose.

• FermBase and CREMER OLEO examined glycerol from fat and oil processing as a potentially cost-effective carbon source for industrial fermentation.
• The paper reported that biodiesel production generated approximately 0.1kg of crude glycerol for every kilogram of biodiesel produced.
• Microorganisms could convert glycerol into products including organic acids, alcohols, lipids, 1,3-propanediol and biodegradable polyhydroxyalkanoates.

Published under the title The Sweet Side of Glycerol: From By-product to Bioprocess Powerhouse, the paper follows glycerol from its origins in fat and oil processing through purification and its potential use as a fermentation feedstock.

Glycerol occurs naturally as the backbone of triglycerides and can be recovered as a co-product when fats and oils are processed through hydrolysis, soap production or transesterification. Biodiesel production is particularly relevant because its expansion is generating growing quantities of crude glycerol.

“Two things are contributing to the increasing interest in glycerol as a fermentation feedstock,” said Gerlis von Haugwitz, Product Manager Fermentation at CREMER. “The supply keeps growing: more biodiesel is being produced, leading to more glycerol as the by-product. And while crude glycerol used to be seen almost as a disposal problem, it is now increasingly viewed as a usable, cost-effective carbon source in fermentation.”

According to the paper, approximately 0.1kg of crude glycerol is generated for every kilogram of biodiesel produced, equivalent to roughly 10% of biodiesel output by weight. Citing the OECD-FAO Agricultural Outlook 2026-2035, the authors noted that continued expansion of global biofuel production could therefore increase the availability of glycerol streams.

Glycerol also differs from conventional fermentation carbon sources such as glucose and starch because material recovered from existing industrial streams does not require dedicated agricultural production.

“Because glycerol sidesteps the competition with the food and feed markets, more companies are actively looking at glycerol as an alternative carbon source to glucose,” von Haugwitz said.

The potential cost advantage, however, becomes more complicated when the composition of crude glycerol is considered.

Crude material can contain water, methanol, salts, fatty acids, soaps, catalyst residues and matter organic non-glycerol, or MONG. Conventional purification can involve filtration, centrifugation, evaporation, acid neutralization and vacuum distillation, depending on the purity required.

FermBase argues that taking glycerol to the highest available purity may not always be necessary. The appropriate grade depends instead on the microorganism, process conditions and impurity profile.

“Crude versus refined glycerol can make a major difference in economics since the carbon source is usually one of the bigger levers of media costs,” von Haugwitz said. “But if the crude material leads to additional cleanup steps, more testing, or worse yields it might not necessarily be more cost efficient.”

The calculation therefore needs to account for the microorganism, equipment, final product and target market rather than simply comparing feedstock prices.

Tolerance to impurities presents another variable. Some strains can withstand compounds such as methanol and salts, while others cannot. Enzymes used within a process can also be affected even when the production organism itself remains tolerant.

“In practice, you have to simply test it with your own strain while using literature findings as a guide,” von Haugwitz said.

Consistency is another consideration for companies contemplating crude glycerol. Composition can vary between batches and suppliers, potentially introducing additional process complexity. According to von Haugwitz, feedstock characterization, optimized feeding strategies and pretreatment may be needed to make yields more reliable.

The paper distinguishes between crude glycerin at approximately 80% purity and several 99.5% refined grades, including technical, food, feed and cosmetic material, as well as pharmaceutical glycerin produced with GMP documentation.

Selecting between them could therefore become a question of finding the lowest level of refinement compatible with reliable fermentation performance.

For companies already operating glucose-based fermentation, moving to glycerol can range from a relatively straightforward process adjustment to a more substantial biological redesign.

“Some yeasts naturally handle glycerol efficiently, making the switch mostly a matter of adjusting the recipe and process conditions,” von Haugwitz said. “When the target product is a secondary metabolite, glycerol might even enhance product yield in comparison to glucose in organisms like Komagataella phaffii and Yarrowia lipolytica.”

Other microorganisms metabolize glycerol differently, meaning achieving suitable yields could require strain engineering.

Glycerol can ultimately be converted by microorganisms into products including 1,3-propanediol, organic acids, alcohols, lipids and biodegradable polyhydroxyalkanoates.

Its appeal as a lower-cost carbon source therefore comes with a trade-off. Less-refined glycerol may reduce raw-material costs, but variability, pretreatment, testing and potential effects on yield all have to enter the calculation. For some fermentation processes, the cheapest grade on paper may not deliver the lowest production cost.

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