The Basis of Wheat Pricing in China: A Detailed Guide to Grading and Classification Indicators

The grading system for wheat in China serves as a comprehensive framework for quality evaluation, market pricing, and processing suitability. Its core function is to provide unified quality standards for wheat trade, storage, and processing. While national standards vary globally, the fundamental evaluation dimensions remain highly consistent. In China, the national standard GB 1351-2008 “Wheat” is the primary basis for wheat classification and circulation, encompassing two core objectives: “Basic Grade Determination” and “Processing Suitability.”

I. Core Grading Indicators and Detailed Explanation

Wheat grading indicators are divided into two categories, which together form a complete quality evaluation system:

1. Mandatory Grading Indicators (determine the basic grade)

2. Key Reference Indicators (determine processing value)

(A) Mandatory Grading Indicators: The “Hard Threshold” for Basic Grade

These indicators are the essential criteria for classifying wheat into Grades 1 through 5 and Substandard Grade. They directly determine the baseline quality qualification.

1. Test Weight (Bulk Density) – Primary Grading Indicator

   • Definition: The weight of wheat per unit volume, measured in grams per liter (g/L). It is the core physical indicator reflecting grain plumpness.

   • Significance: Higher test weight indicates plumper, denser kernels with thinner bran, leading to higher flour yield and better flour quality. It is the foremost criterion for grade determination.

2. Unsound Kernels – Quality Deduction Factor

   • Definition: Kernels with compromised quality due to disease, damage, etc., but which still retain some use value. Specific types include:

     • Diseased Kernels: Kernels with visible disease spots, affecting food safety.

     • Scabby Kernels (Fusarium-damaged): Kernels shriveled, dull white, or pinkish-red due to scab infection. Strict limits are set by the national standard due to associated mycotoxins.

     • Black Embryo Kernels: Kernels with a dark brown or black embryo, affecting germination and processing quality.

     • Sprouted Kernels: Kernels where the sprout or radicle has broken through the seed coat, degrading processing performance.

     • Moldy Kernels: Kernels with mold growth on the surface, posing safety risks.

     • Damaged/Broken Kernels: Crushed or broken kernels, reducing flour yield.

     • Insect-damaged Kernels: Kernels damaged by insect boring, compromising kernel integrity.

   • Significance: The content of unsound kernels is negatively correlated with wheat quality. It directly impacts flour yield and can lead to storage mold or food safety issues, making it a key deduction factor in grading.

3. Foreign Material (Impurities) – Purity Indicator

   • Definition: Non-edible or worthless matter mixed with the wheat, categorized as:

     • Screenings: Small impurities passing through a specified sieve (typically a 1.5mm round-hole sieve).

     • Mineral Matter: Inorganic impurities like sand, gravel, cinder, or brick fragments, affecting safety.

     • Other Organic Matter: Worthless wheat kernels, kernels of other grains, weed seeds, etc.

   • Significance: Foreign material content directly determines purity. Excessive impurities reduce usable value and can damage processing equipment, necessitating strict control.

4. Moisture Content – Safe Storage Indicator

   • Definition: The water content within wheat kernels, a critical factor for storage stability.

   • Significance: Excessively high moisture easily leads to heating, mold, and insect infestation. The national standard sets a maximum limit (typically ≤12.5%). While not used for grade promotion, it is a safety indicator subject to “one-vote veto”; wheat must meet the limit to be acceptable.

5. Color & Odor – Sensory Baseline

   • Definition: The inherent color, luster (normal wheat is light yellow or golden with natural gloss), and natural wheat aroma.

   • Significance: These sensory indicators are fundamental for judging freshness and the absence of deterioration. Off-odors (moldy, sour, chemical) or severe discoloration (e.g., blackening, graying) lead to direct disqualification from normal trade.

(B) Key Reference Indicators: The “Watershed” for Processing Value

These indicators do not affect the basic grade but directly determine wheat’s processing specialty and market premium, serving as core references for trade pricing.

1. Hardness Index – Basis for Wheat Type Classification

   • Definition: A physical parameter reflecting kernel hardness. The national standard classifies:

     • Hard Wheat: Hardness Index ≥60, hard texture, vitreous endosperm dominant.

     • Soft Wheat: Hardness Index ≤45, soft texture, mealy endosperm dominant.

     • Mixed Type: Hardness Index between 46-59.

   • Significance: Hardness dictates processing characteristics. Hard wheat offers higher flour yield and stronger gluten, while soft wheat yields lower but finer flour. It is the key basis for classifying processing types.

2. Protein Content & Gluten Quality – Core Functional Characteristics

   • Definition:

     • Protein Content: The mass percentage of crude protein in wheat (dry basis), the foundation for gluten formation.

     • Wet Gluten Content: The weight percentage of hydrated gluten remaining after washing flour (often required ≥22%).

     • Stability Time: Measured by a farinograph, it indicates the duration dough maintains stability during mixing, directly reflecting gluten strength.

   • Significance: Determines the “gluten type,” clarifying processing suitability:

     • Strong Gluten Wheat: Protein ≥14%, Wet Gluten ≥30%, Stability Time ≥10 min. Suitable for bread, stretched noodles, premium dumpling flour.

     • Medium Gluten Wheat: Protein 11-13%, Wet Gluten 24-28%, Stability Time 3-7 min. Suitable for steamed buns, noodles, Chinese pastries.

     • Weak Gluten Wheat: Protein ≤10.5%, Wet Gluten ≤22%, Stability Time ≤2.5 min. Suitable for cakes, cookies, pastries.

3. Falling Number – Sprout Damage Indicator

   • Definition: Measured by a falling number apparatus, it indicates α-amylase activity in wheat, in seconds (s).

   • Significance: Falling number is inversely related to amylase activity. A low value (typically <200s) indicates sprouting, with high amylase activity leading to sticky dough, poor fermentation, sticky bread crumb, and brittle noodles. A normal value (250-350s) indicates sound, non-sprouted wheat with stable processing performance. It is a key indicator for detecting sprout damage.

II. Example of Wheat Grade Classification under China’s National Standard

Based on mandatory indicators like test weight and unsound kernels, wheat is classified as shown below:

Note: Moisture, foreign material, color, and odor must all meet the unified requirements of the national standard. Failure in any of these results in disqualification, regardless of other grades.

III. Interrelationships and Practical Application

• Link Between Basic Grade and Processing Value: Mandatory indicators determine “if wheat is qualified” and its “basic grade,” while reference indicators determine its “processing use” and “market price.” Under similar basic grades, strong gluten wheat commands a 10%-30% price premium over medium gluten wheat. Weak gluten wheat also holds a premium for its suitability in pastry processing.

• Evaluation Logic in Trade & Processing: The practical workflow follows a “Grade First, Type Second” sequence:

  1. Step 1: Determine the basic grade (1-5 or Substandard) based on mandatory indicators.

  2. Step 2: Identify the processing type (Strong/Medium/Weak Gluten) using the hardness index, protein, and gluten quality.

  3. Step 3: Refine pricing using indicators like unsound kernels and falling number. For example, Grade 1 Strong Gluten wheat free of scabby kernels and with normal falling number commands the highest price, while Substandard sprouted wheat (low falling number) circulates at a discount for specific uses.

• Core Value of the System: China’s wheat grading system ensures consumer food safety (via controls on moisture, impurities, scabby kernels), meets processors’ specific needs (via gluten type matching), and provides a transparent pricing basis for trading partners. It achieves a triple balance of Quantity (flour yield), Quality (safety), and Functionality (processability).