Earthy Off-Flavor in Beetroot: Formation Mechanisms and Full-Chain Removal Strategy

In the beet and beetroot powder industry, the characteristic earthy off-flavor has long been an unavoidable quality pain point. For decades, the industry has widely attributed this flavor to unclean soil or insufficient washing, and attempted to address it through deep cleaning and post-harvest deodorization processes—yet the results have remained inconsistent.In reality, the earthy and musty profile of beets is a typical multi-source flavor phenotype, comprising an inherent baseline from endogenous plant metabolism plus exogenous contamination from soil and water sources. A landmark study published in HortScience in 2018 confirmed the endogenous production of geosmin in beets. When viewed alongside the distribution logic of China’s beet producing regions, it becomes clear that gaps in raw material quality are determined from the very first steps of variety selection and site selection. Remedial measures at a single stage can only treat the symptoms; full-chain proactive control is the core of differentiated quality.

1. Origins of Beet Earthy Off-Flavor

The core compounds responsible for beet earthy off-flavor fall into three categories: geosmin, 2-methylisoborneol (2-MIB), and pyrazines. All three have extremely low odor thresholds (detectable by humans at the ng/L level), and their cumulative effect creates the signature earthy, musty, and muddy notes of beet products.These compounds originate from three independent yet overlapping pathways—endogenous metabolism, exogenous soil microbiota, and irrigation water enrichment—which explains why the earthy flavor of conventional beets is difficult to eliminate completely.

1.1 Endogenous Metabolism: An Inherent Trait Encoded in Genes

This is the most overlooked yet most fundamental source. Beets possess a complete terpenoid metabolic pathway and can synthesize geosmin autonomously, independent of any external microorganisms.A research team at the University of Wisconsin–Madison verified this through aseptic tissue culture experiments. In a completely sterile environment isolated from soil microorganisms, and confirmed to be free of functional bacterial contamination via 16S rRNA high-throughput sequencing, beet plants still produced detectable levels of geosmin consistently. For some cultivars, geosmin concentrations were even higher in sterile-grown plants than in field-grown counterparts. The core biosynthetic pathway proceeds from farnesyl diphosphate (FPP) via sesquiterpene synthase catalysis, through sequential cyclization steps to form geosmin—making it an inherent product of beet secondary metabolism.
This explains why beets retain a baseline earthy flavor no matter how thoroughly they are washed: this fraction of the flavor exists inside plant cells and cannot be removed by physical methods such as washing or peeling. Genotypic differences between cultivars directly determine geosmin biosynthetic capacity, and represent the primary genetic determinant of inherent earthy flavor intensity.

1.2 Exogenous Soil Sources: Adhesion and Penetration of Microbial Metabolites

Soil is the main carrier of exogenous earthy off-flavor. Soil microbiota such as Streptomyces and actinomycetes continuously secrete geosmin and 2-MIB as byproducts of organic matter decomposition. These compounds adhere to the surface of beet taproots and gradually penetrate into the outer pulp layers through epidermal pores, amplifying overall earthy and musty notes.
Soil texture and environmental conditions directly determine the severity of exogenous off-flavor. In heavy clay soils, high-organic-matter fields, and low-lying waterlogged areas, flavor-producing microbes thrive, and exogenous earthy flavor in beets increases significantly. In contrast, sandy, dry, low-organic-matter soils support lower microbial activity and abundance, resulting in lighter exogenous contamination.

1.3 Irrigation Water Enrichment: Secondary Flavor Accumulation

2. Industrial Logic of China’s Beet Producing Regions: Selection Criteria for Sugar Production vs. Flavor Quality

China’s traditional beet producing regions were established primarily around the needs of the sugar manufacturing industry, concentrated in three major cool agricultural belts—Northeast China, Northwest China, and North China—spanning 35°–50° north latitude. The cool climate and large diurnal temperature variation in this zone perfectly match the sugar accumulation characteristics of beets, supporting a complete domestic sugar beet industrial system.
For sugar production, yield, sugar content, and disease resistance are the core evaluation metrics; flavor attributes such as earthy off-flavor have not been a primary focus of breeding and cultivation. Each of the three major regions has developed distinct industrial strengths:
Northeast China: Centered in Heilongjiang, this is China’s traditional core beet producing region. Its fertile black soils, cool summers, and stable water resources support stable, high-yield beet production with balanced sugar accumulation, making it the backbone of domestic sugar beet supply.
Northwest China: Represented by Xinjiang and Gansu, this region benefits from intense sunlight and extreme diurnal temperature variation, producing beets with exceptionally high sugar content. The dry climate also reduces disease pressure, making it a premium region for high-sugar beets.
North China: Mainly located in central Inner Mongolia and northern Hebei, this region leverages beets’ salt tolerance to adapt to local soil conditions. Its proximity to sugar manufacturing hubs brings mature industrial support and cost advantages in transportation and processing.
For beetroot powder targeting the functional food and clean-label markets, flavor purity, pesticide residue control, and contaminant management are more critical quality requirements. Using general-purpose varieties and cultivation models from traditional sugar beet regions creates a natural misalignment for flavor control. This is the rationale behind our full-chain odor mitigation system spanning variety selection, cultivation base, and processing technology.

3. Full-Chain Differentiated Mitigation System: Proactive Root-Cause Reduction Rather Than End-of-Pipe Masking

Because earthy off-flavor arises from the combination of an endogenous baseline, soil adhesion, and water enrichment, end-of-pipe measures such as washing and post-processing deodorization can only remove surface exogenous odors and cannot address the endogenous baseline, resulting in limited and unstable efficacy.
Based on a mechanistic understanding of earthy off-flavor formation and our commitment to high-quality raw materials, we have moved beyond the general selection logic of traditional sugar beet regions and established a three-dimensional mitigation framework of variety–cultivation base–processing technology. Targeting all three sources of off-flavor, we achieve stable, controllable reduction of earthy flavor in beetroot powder without relying on external masking agents.

3.1 Directed Breeding of Low-Geosmin Cultivars: Anchoring a Low Flavor Baseline at the Genetic Level

We select a dedicated low-geosmin beet cultivar (Beta vulgaris L.) that controls flavor from both endogenous and exogenous directions, lowering the inherent earthy flavor baseline from the genetic level.
Endogenous regulation: This cultivar shows significantly downregulated gene expression of key enzymes in the geosmin biosynthetic pathway, with lower flavor-producing activity in the terpenoid metabolic pathway. The conversion efficiency from FPP to geosmin is greatly reduced, cutting the endogenous baseline earthy flavor at its source.
Exogenous defense: The cultivar also features superior taproot morphology: a smooth, tight epidermis with dense cortical tissue and few surface pores. This effectively blocks embedding and penetration of soil particles and flavor-producing microbes, physically reducing the invasion of exogenous off-flavor compounds.

3.2 High-Altitude Dedicated Cultivation Base: Natural Barriers Block Exogenous Input

Our beet cultivation base is located in high-altitude alluvial sandy land in Qinghai. Leveraging the unique local geographic and climatic conditions, we have built a triple natural protection network of soil, climate, and water, minimizing the potential for exogenous off-flavor formation.
Dual-action flavor control from cool high-altitude climate: The cool high-altitude environment maintains steady beet growth, avoiding secondary metabolic disruption and abnormal geosmin accumulation caused by heat stress, and keeping endogenous flavor production at a low, stable level. Additionally, low temperatures directly inhibit the reproduction and metabolism of Streptomyces and actinomycetes in soil; combined with intense sunlight and high ultraviolet radiation that naturally deactivate surface soil microbes, this greatly reduces the population and activity of flavor-producing microorganisms.
Low-microbial environment from alluvial sandy soil: The alluvial sandy soil has excellent aeration and drainage, with low organic matter and humus content. This environment is naturally unfavorable for the colonization and reproduction of flavor-producing microbiota, reducing the potential input of soil-derived geosmin at the environmental source.
Clean irrigation with glacial meltwater: Irrigation uses pure snow and glacial meltwater throughout the growing season. The water source is free of eutrophication risks and the cyanobacterial blooms common in conventional agricultural irrigation, completely cutting off the enrichment pathway of water-borne off-flavor and achieving zero odor input from the water source.

3.3 Precision Processing Technology: Natural Balancing + Texture Optimization for Residual Flavor Reduction

For the trace residual earthy flavor remaining after variety and cultivation control, we do not rely on external masking agents. Instead, we optimize both flavor and mouthfeel by combining beets’ inherent properties with tailored processing technology.
Beetroot powder naturally has high sucrose content, which provides a mild, sweet balancing effect. Through precise ultra-fine grinding with controlled particle size, we achieve full cell breakage and full release of endogenous sugars, which naturally neutralize residual trace earthy flavor. At the same time, the fine, uniform powder delivers a smooth, non-gritty mouthfeel, solving the common pain points of rough texture and throat irritation in conventional beetroot powder products.

Conclusion

It is often said that beet earthy flavor is innate and cannot be removed—but this is essentially a conclusion rooted in limited understanding of crop metabolic mechanisms and regional endowments.
From general-purpose sugar beet varieties to directed low-geosmin cultivars, from traditional production regions to dedicated high-altitude bases in Qinghai, from end-of-pipe remediation to full-chain proactive control, every choice represents a redefinition of raw material quality. By shifting the focus of flavor control from late-stage masking to early-stage selection, and aligning every step—from genetics to environment to processing—with the underlying mechanisms, we can consistently produce low-earthy-flavor, high-quality beetroot powder without additional additives.
Ultimately, the depth of understanding of raw material fundamentals determines the level of product competitiveness.

Reference：

Maher, L., & Goldman, I. L. (2018). Endogenous Production of Geosmin in Table