Two-Stage Fermentation Removes 95-99% of Off-Odors from Plant Proteins

Smell drives food choice more than most people realize. Before a bite is taken, aroma already shapes whether a food seems appetizing or repellent - and for plant-based proteins, that pre-bite judgment is often a barrier. Soy protein smells beany. Pea protein smells grassy. Hemp protein smells earthy. Faba bean protein smells sulfurous. These are not subjective quirks: they are the product of specific volatile compounds released during cultivation, processing, and storage of legume and grain proteins.

A team at Ohio State University led by food science professor Sheryl Barringer and PhD student Manpreet Kaur set out to neutralize those odors without adding cost or complexity to production. Their solution - a two-stage fermentation process that attacks off-odor compounds sequentially - removed between 95% and 99% of key smells across eight different plant proteins, outperforming single-stage fermentation in every case. The study was published in the journal Foods.

Why Plant Protein Smell Is a Significant Problem

Consumer surveys consistently rank taste and smell as the primary reasons people reject plant-based products. This is a commercially relevant gap: the global market for plant-based proteins is growing as consumers seek more sustainable and allergen-friendly diets, but adoption plateaus when products smell or taste noticeably different from familiar dairy and meat alternatives. Manufacturers have used physical and chemical processing - heat treatment, enzyme addition, pH adjustment - to reduce off-odors, but these methods can degrade nutritional quality, alter texture, or introduce their own undesirable flavors.

Fermentation is an attractive alternative because it uses bacteria to biologically transform the compounds responsible for off-odors rather than merely masking or removing them. Standard single-stage fermentation already reduces plant protein odors somewhat, but the OSU team found this insufficient for the most pungent compounds.

Two Stages, Two Bacterial Cultures

The OSU approach divides the fermentation into two distinct phases with different bacterial cultures optimized for different tasks. In the first stage, Lactobacillus plantarum - a broadly used probiotic bacterium also found in fermented vegetables like sauerkraut - is introduced and given time to metabolize the specific aldehyde and ketone compounds most responsible for beany, grassy, and earthy odors. This stage targets the problem at its chemical source.

In the second stage, a traditional yogurt culture containing mixed bacteria species associated with desirable dairy-like aromas takes over. This phase does not just continue off-odor reduction - it actively develops pleasant, neutral flavors that make the final product smell more like familiar fermented dairy and less like raw legume.

"We are using the same things that are used in the normal fermentation process," said Kaur. "The only thing changed is how we utilize the bacteria."

The timing and sequencing matter: allowing L. plantarum to work first, before the yogurt culture, proved more effective than either culture alone or a simultaneous combination. The two stages do not add significant processing time - fermentation already takes anywhere from a few hours to a day depending on the product, and the two-step approach operates within that same window.

Results Across Eight Proteins

The team tested the method on 9% protein solutions of: soy, pea, chickpea, mung bean, faba bean, rice, barley-rice blend, and hemp. Human sensory evaluation - rather than purely instrumental measurement - confirmed the odor reductions. Panelists rated off-odor intensity before and after fermentation, providing a direct measure of what a consumer would actually perceive.

Reductions ranged from 95% to 99% of key off-odors across all eight proteins, with some achieving near-complete elimination. The consistency across a diverse set of protein sources - ranging from legumes to cereals to a seed - suggests the two-stage bacterial approach addresses a common mechanism of odor generation rather than one specific to a particular crop.

Additive testing showed some nuance in the process. The rare sugar allulose enhanced L. plantarum activity in the first stage. Strawberry preserves improved the performance of the yogurt culture in the second stage. Structuring agents commonly used in food manufacturing - pectin, xanthan gum, and added oil - had minimal effect on odor reduction, meaning manufacturers can still include these functional ingredients without compromising the fermentation outcome.

Practical Path to Application

The approach is designed for direct integration into existing plant-based dairy manufacturing. It does not require new equipment, novel chemical inputs, or extended production timelines. The bacterial cultures are already established in food-grade fermentation globally. This lowers the barrier to adoption compared with techniques that require novel processing infrastructure.

The study was conducted at laboratory scale with controlled protein solutions. Industrial scaling would need to confirm that the odor reduction performance holds with the variation inherent in commercial protein concentrate batches - which differ in purity, lipid content, and residual compounds depending on crop source and extraction method. Whether the improved aroma translates into consumer acceptance in actual final products, including products with added fats, sugars, and texturizers, also requires further testing beyond the current paper's scope.