Raw Potato Material Quality Grading System¶
Document Code: HJ-QC-FC-004
Version: 3.0
Effective Date: 2026-04-01
Issued by: Hongji Agriculture — Quality Control & Raw Material Procurement Division
Applicable to: All incoming fresh potato lots delivered to the Zhangjiakou processing facility for potato flake and powder production.
1. Purpose and Scope¶
This document establishes the standardized quality grading system for raw (fresh) potatoes procured for Hongji Agriculture's potato processing facility. The system defines:
- Measurable quality parameters and their acceptance thresholds
- A three-tier grading classification (Grade A, Grade B, Grade C)
- Rejection conditions (unconditional and conditional)
- Sampling protocols based on Acceptable Quality Limit (AQL) standards
- Inspection workflow from truck arrival to lot acceptance
- Grade-to-price linkage mechanism
This grading system applies to all contract growers, company farms, and third-party suppliers delivering Atlantic, Shepody, and Russet Burbank varieties to the Zhangjiakou plant.
2. External Quality Parameters (Visual/Tactile Inspection)¶
2.1 Tuber Size Classification¶
Size is determined by the maximum transverse diameter using mechanical or optical graders. Size is the primary stratification parameter for processing lines.
| Size Code | Diameter Range (mm) | Weight Range (g) | Processing Line Suitability |
|---|---|---|---|
| S | 30–45 | 30–80 | Marginal — low yield efficiency; acceptable for powder only |
| M | 45–65 | 80–160 | Optimal for flakes and powder |
| L | 65–85 | 160–300 | Optimal (may need adjustment for flake slicer gap) |
| XL | > 85 | > 300 | Unacceptable — oversize; increases reject rate |
Note: A single lot must have ≥ 80% of tubers in the M + L combined categories to qualify for Grade A. Lots with > 10% XL tubers are automatically downgraded one grade.
2.2 Shape Classification¶
Shape uniformity is critical for peel loss minimization and consistent processing.
| Shape Class | Description | Acceptability |
|---|---|---|
| Round to oval | Length-to-width ratio 0.8–1.3; uniform contour | Preferred (Atlantic standard) |
| Long oval to oblong | Length-to-width ratio 1.3–2.0; slightly elongated | Acceptable (Russet Burbank, Shepody) |
| Irregular | Dumbbell, bottleneck, pear-shaped, knobby | Acceptable up to 8% of lot |
| Severely misshapen | Deep convolutions, multiple constrictions, asymmetrical | Reject — excessive peel loss |
2.3 External Defect Evaluation¶
| Defect Category | Defect Type | Grade A Max (%) | Grade B Max (%) | Grade C Max (%) |
|---|---|---|---|---|
| Mechanical damage | Deep cuts (> 3 mm depth) | 1.0 | 3.0 | 5.0 |
| Skinning (> 25% surface area) | 3.0 | 8.0 | 12.0 | |
| Shatter bruise (> 5 mm diameter) | 2.0 | 5.0 | 8.0 | |
| Pressure bruising (depressed, blackened area) | 1.0 | 3.0 | 5.0 | |
| Greening | > 10% surface greening (solanine) | 0 | 1.0 | 2.0 |
| 5–10% surface greening | 1.0 | 3.0 | 5.0 | |
| < 5% surface greening (trace) | 2.0 | 5.0 | 10.0 | |
| Disease / rot | Late blight (P. infestans) lesions | 0 | 0 | 1.0 |
| Bacterial soft rot (Pectobacterium spp.) | 0 | 0 | 0 (reject) | |
| Fusarium dry rot | 0.5 | 1.5 | 3.0 | |
| Common scab (surface area affected > 5%) | 3.0 | 8.0 | 15.0 | |
| Powdery scab (any visible lesion) | 1.0 | 3.0 | 5.0 | |
| Insect damage | Wireworm holes (any) | 1.0 | 3.0 | 5.0 |
| Colorado potato beetle grub damage | 0.5 | 1.0 | 2.0 | |
| Tuber moth damage | 0 | 0.5 | 1.0 | |
| Physiological defects | Growth cracks (healed, < 2 mm wide) | 2.0 | 5.0 | 8.0 |
| Growth cracks (unhealed or > 2 mm) | 0 | 1.0 | 2.0 | |
| Secondary growth / chain tubers | 1.0 | 3.0 | 5.0 | |
| Hollow heart (externally visible on cut surface) | 0 | 1.0 | 2.0 | |
| Foreign material | Soil / stones / debris | 1.0% by weight | 2.0% by weight | 3.0% by weight |
| Stems, leaves, other vegetable matter | 0.5% by weight | 1.0% by weight | 2.0% by weight |
Note: All defect percentages are by weight of a representative sample (minimum 25 kg).
3. Internal Quality Parameters (Laboratory-Analyzed)¶
3.1 Dry Matter¶
Measured by oven-drying method (105 °C for 16 h) or equivalent NIR-instrument calibrated to oven-dry basis.
| Grade | Dry Matter (% FW) | Suitability |
|---|---|---|
| Grade A | ≥ 21.0% | Premium for both flakes and powder |
| Grade B | 19.5–20.9% | Acceptable; marginally lower process yield |
| Grade C | 18.0–19.4% | Conditional acceptance (must pass reducing sugar test and obtain QA manager approval) |
| Reject | < 18.0% | Unacceptable for processing |
3.2 Reducing Sugars¶
Glucose + fructose, expressed as % of fresh weight. Determined by glucose oxidase/peroxidase (GOD/POD) enzymatic method or HPLC.
| Grade | Reducing Sugar (% FW) | Flake Color Prediction | Acrylamide Risk |
|---|---|---|---|
| Grade A | ≤ 0.20 | Excellent (L* ≥ 83) | Low |
| Grade B | 0.21–0.30 | Good (L* 79–82) | Moderate |
| Grade C | 0.31–0.40 | Acceptable (L* 75–78) | Elevated |
| Reject | > 0.40 | Unacceptable (L* < 75) | High — reject |
3.3 Specific Gravity¶
Measured by weight-in-air / weight-in-water method at 15 °C.
| Grade | Specific Gravity | DM Equivalent (approx.) |
|---|---|---|
| Grade A | ≥ 1.088 | ≥ 21.5% |
| Grade B | 1.082–1.087 | 20.0–21.4% |
| Grade C | 1.075–1.081 | 18.5–19.9% |
| Reject | < 1.075 | < 18.5% |
3.4 Internal Defects¶
| Defect | Description | Grade A Max (%) | Grade B Max (%) | Grade C Max (%) |
|---|---|---|---|---|
| Hollow heart | Central cavity > 10 mm diameter | 1.0 | 3.0 | 5.0 |
| Internal brown spot / heat necrosis | Brown necrotic flecks in medullary tissue > 5% cross-section | 1.0 | 3.0 | 5.0 |
| Black heart | Internal blackening due to oxygen deficiency | 0 | 0 | 0.5 |
| Glassy end / translucent end | Sugar-end; glassy or water-soaked tissue at stem end | 1.0 | 3.0 | 5.0 |
| Internal sprouting | Sprouts visible inside tuber | 0 | 0 | 0 (reject) |
| Brown center | Lignified central discoloration | 1.0 | 3.0 | 8.0 |
3.5 Variety Authenticity¶
Each lot must correspond to the declared variety. Verification is performed by tuber morphology (shape, skin color, eye depth, flesh color) and optionally by molecular markers (SSR fingerprinting) for disputed lots. Misidentification results in Grade C or rejection at the buyer's discretion.
| Variety | Skin Color | Flesh Color | Eye Depth | Shape |
|---|---|---|---|---|
| Atlantic | Light buff / tan | White to cream | Shallow | Round to oval |
| Shepody | White to light buff | White | Shallow to medium | Long oval to oblong |
| Russet Burbank | Russet (netted, brown) | White | Medium to deep | Long oblong |
4. Comprehensive Grade Definitions¶
4.1 Grade A — Premium Processing Quality¶
| Parameter | Requirement | Test Frequency |
|---|---|---|
| Variety | Declared variety confirmed | Every load |
| Dry matter | ≥ 21.0% | Every load (NIR rapid test) |
| Reducing sugars | ≤ 0.20% | Every load (GOD/POD dipstick) |
| Tubers in M + L size range | ≥ 80% by weight | Every load (mechanical grader) |
| XL tubers (> 85 mm) | ≤ 5% | Every load |
| Total external defects | ≤ 10% cumulative (none exceeding individual Grade A max) | Composite from 25 kg sample |
| Green tubers (> 10% greening) | Zero tolerance | Visual |
| Rot / decay | Zero tolerance | Visual + sniff |
| Foreign material | ≤ 1.0% by weight | Every load |
| Internal defects (hollow heart, IBN, glassy end combined) | ≤ 3% | 5 of 10 tubers cut longit/transverse |
Price premium: +10% over base contract price.
4.2 Grade B — Standard Processing Quality¶
| Parameter | Requirement |
|---|---|
| Dry matter | 19.5–20.9% |
| Reducing sugars | 0.21–0.30% |
| Tubers in M + L size range | ≥ 65% |
| Total external defects (within Grade B max limits) | ≤ 20% cumulative |
| Rot / decay | Zero tolerance |
| Foreign material | ≤ 2.0% by weight |
Price: Base contract price.
4.3 Grade C — Conditional Acceptance¶
| Parameter | Requirement |
|---|---|
| Dry matter | 18.0–19.4% |
| Reducing sugars | 0.31–0.40% |
| Tubers in M + L size range | ≥ 50% |
| Total external defects (within Grade C max limits) | ≤ 35% cumulative |
| Rot / decay | < 1% (any > 1% = unconditional rejection) |
| Foreign material | ≤ 3.0% by weight |
Price deduction: –15% from base contract price. Requires written conditional acceptance from the QA Manager and Raw Material Procurement Manager. Lot must be processed within 48 hours (cannot be stored for more than 3 days).
5. Rejection Criteria¶
5.1 Unconditional Rejection¶
The following conditions result in immediate rejection of the entire lot. The supplier bears all demurrage and return transport costs.
| Condition | Rationale |
|---|---|
| Dry matter < 18.0% | Technically unprocessable — insufficient starch to produce flakes |
| Reducing sugars > 0.40% | Unacceptable product color and acrylamide risk |
| Any visible soft rot (bacterial soft rot) | Contamination risk to entire receiving bay |
| Frozen tubers (translucent, water-soaked) | Complete loss of texture; rapid spoilage |
| Multiple varieties mixed in same load | Cannot adjust process parameters for mixed varieties |
| Foreign material > 5% by weight | Excess dirt, stones, or debris damages processing equipment |
| Unconditional reject: external green > 25% of any sample tuber | Solanine (glycoalkaloid) toxicity risk to consumers |
| Live insects or visible rodent contamination | Food safety violation |
| Phytosanitary non-compliance | Regulatory requirement |
5.2 Conditional Rejection (Option to Downgrade)¶
The buyer may, at their discretion, accept these lots at a Grade C price or reject outright:
| Condition | Offered Options |
|---|---|
| Dry matter 17.5–18.0% (borderline) | Reject or accept at Grade C – additional 10% penalty |
| Reducing sugars 0.35–0.40% with dry matter > 20% | Accept for powder-only production at Grade C – 10% penalty |
| > 10% but < 20% green tubers | Manual removal (supplier labor) + Grade B or C penalty |
| > 5% foreign material but < 10% | Deduction of foreign material weight × 2 + cleaning fee |
6. Sampling Protocol (Based on AQL Standards)¶
6.1 Sampling Method¶
Sampling follows ANSI/ASQ Z1.4 (ISO 2859-1) — single sampling plan, normal inspection level II, with AQLs tailored to each defect class:
| Defect Class | AQL (%) | Description | Criticality |
|---|---|---|---|
| Critical | 0 | Rot, frozen, green > 25%, foreign material > 5% | Food safety / process risk |
| Major | 1.5 | Dry matter below grade minimum, reducing sugars above grade max, hollow heart, deep cuts, chain tubers | Direct impact on processing quality |
| Minor | 4.0 | Skinning, scab, slight greening (< 10%), minor growth cracks, wireworm holes ≤ 3 | Appearance or marginal processing effect |
6.2 Lot Size and Sample Size Determination¶
| Lot Size (tons) | Sample Size (kg) | Sample Size (number of tubers)* | Critical Defects | Major Defects | Minor Defects |
|---|---|---|---|---|---|
| ≤ 5 | 10 | ~50 | 0 | ≤ 2 | ≤ 5 |
| 6–15 | 15 | ~75 | 0 | ≤ 3 | ≤ 8 |
| 16–30 | 25 | ~125 | 0 | ≤ 5 | ≤ 12 |
| 31–50 | 35 | ~175 | 0 | ≤ 7 | ≤ 18 |
| 51–100 | 50 | ~250 | 0 | ≤ 10 | ≤ 25 |
| > 100 | 60 | ~300 | 0 | ≤ 12 | ≤ 30 |
*Based on average 200 g tuber weight. Adjust proportionally for smaller/larger tubers.
6.3 Sampling Procedure¶
- Primary sampling: Five grab samples of approximately 5 kg each from different locations within the truck/trailer (front, mid-front, mid-rear, rear, and center top layer).
- Mixing and reduction: Combine all primary samples; use quartering method to reduce to the required sample weight.
- Immediate visual grading: Perform external defect assessment within 30 minutes of sampling.
- Laboratory submission: A 10 kg subsample is sent to the QA laboratory for specific gravity, dry matter, and reducing sugar analysis. Results must be reported within 60 minutes.
- Hold condition: The entire lot is placed on HOLD pending laboratory results. The truck is not permitted to unload until QA clears the lot.
7. Receiving Inspection Workflow¶
7.1 Step-by-Step Receiving Procedure¶
Step 1: Truck Arrival & Document Check
├── Verify supply agreement / delivery order
├── Confirm variety, field lot number, and origin farm
├── Check harvest date (must be within previous 72 hours)
└── Record truck temperature (target 8–15 °C)
Step 2: Visual Pre-Inspection (5 minutes)
├── Observe overall appearance from truck top
├── Check for visible rot odor, excessive mud, greening
├── If obvious unconditional reject condition visible → reject immediately without sampling
└── If pass → proceed to sampling
Step 3: Sampling (15 minutes)
├── Extract 5 grab samples as per Section 6.3
├── Transport to QA lab (sealed, labeled poly bag)
└── Initiate lab analysis
Step 4: External Grading (20 minutes)
├── Transfer sample to grading table
├── Assess size distribution (mechanical grader or template)
├── Assess shape (visual classification)
├── Weigh and categorize all external defects
├── Record defect percentages
└── Assign preliminary external grade
Step 5: Internal Grading / Laboratory (40 minutes)
├── Specific gravity measurement (weight-in-water method)
├── Dry matter (NIR rapid test; confirm via oven dry if in dispute)
├── Reducing sugars (GOD/POD enzymatic test)
├── Internal defect assessment (cut 50 tubers longitudinally and 10 transversely)
└── Calculate final internal grade
Step 6: Grade Determination & Disposition (10 minutes)
├── Combine external + internal grade → final lot grade
├── If final grade C: notify QA Manager and Raw Material Manager
├── If reject: complete rejection form, notify supplier
├── If accept: assign lot ID in ERP system, direct to storage or processing line
└── Generate Receiving Certificate
Total turnaround time target: 90 minutes from truck arrival to disposition
7.2 Dispute Resolution¶
| Scenario | Resolution Process |
|---|---|
| Supplier disputes grade | Retain sealed duplicate sample; send to independent lab (China Agricultural University or Beijing Potato Research Center) at supplier's cost. If independent test confirms higher grade, Hongji pays testing costs + grade adjustment. |
| Borderline result (± 0.1% DM or ± 0.02% reducing sugar) | Benefit of doubt given to supplier for Grade A/B boundary; QA Manager decides for Grade B/C boundary |
| Grade dispute arbitration | Final arbitration by Hongji Quality Director; decision binding per supply agreement |
8. Grade-to-Price Linkage Mechanism¶
8.1 Base Price Structure¶
The base contract price is established per supply season (negotiated annually) and is adjusted according to the following table:
| Grade | Price Index | Adjustment |
|---|---|---|
| Grade A | 1.10 | Base price × 1.10 |
| Grade B | 1.00 | Base price × 1.00 |
| Grade C | 0.85 | Base price × 0.85 |
| Reject | 0.00 | Not purchased |
8.2 Incremental Deductions (Applied cumulatively)¶
| Condition | Deduction |
|---|---|
| Foreign material > 1.0% (Grade A) or > 2.0% (Grade B) | Deduct actual % above threshold from net weight |
| Tuber moth damage present | –2% additional deduction |
| Smell of silage / fermentation | –5% deduction |
| Received > 72 h after harvest without refrigeration | –5% deduction |
| Received with pulp temperature > 20 °C | –3% deduction |
| Truck delivered more than 30 min late to scheduled time slot (without prior notice) | –2% per incident |
8.3 Bonus for Exceptional Quality¶
| Condition | Bonus |
|---|---|
| Dry matter ≥ 23.0% AND reducing sugars ≤ 0.12% | +5% on Grade A price |
| Deliveries with > 95% Grade A across season | +2% season-end rebate |
| Zero reject loads across entire contract year | +3% season-end rebate |
9. Quality Specification Sheet (Quick Reference Card)¶
Potato Flake Processing — Raw Material QC Card¶
| Parameter | Grade A | Grade B | Grade C | Reject |
|---|---|---|---|---|
| Dry matter (% FW) | ≥ 21.0 | 19.5–20.9 | 18.0–19.4 | < 18.0 |
| Reducing sugar (%) | ≤ 0.20 | 0.21–0.30 | 0.31–0.40 | > 0.40 |
| Specific gravity | ≥ 1.088 | 1.082–1.087 | 1.075–1.081 | < 1.075 |
| Size M + L (%) | ≥ 80 | ≥ 65 | ≥ 50 | — |
| XL (> 85 mm) (%) | ≤ 5 | ≤ 10 | ≤ 15 | > 15 |
| Total external defects (%) | ≤ 10 | ≤ 20 | ≤ 35 | > 35 |
| Green > 10% surface (%) | 0 | ≤ 1 | ≤ 2 | > 2 |
| Rot / decay (%) | 0 | 0 | < 1 | ≥ 1 |
| Foreign material (% wt) | ≤ 1.0 | ≤ 2.0 | ≤ 3.0 | > 5.0 |
| Varietal purity (%) | 100 | 100 | 100 | < 100 |
| Internal defects (%) | ≤ 3 | ≤ 8 | ≤ 12 | > 12 |
Potato Powder Processing — Relaxed Raw Material QC Card¶
| Parameter | Acceptable | Reject |
|---|---|---|
| Dry matter (% FW) | ≥ 18.5 | < 18.5 |
| Reducing sugar (%) | ≤ 0.35 | > 0.40 |
| Specific gravity | ≥ 1.078 | < 1.075 |
| Rot / decay (%) | 0 | > 0.5 |
| Foreign material (% wt) | ≤ 3.0 | > 5.0 |
10. Compliance and Audit¶
10.1 Supplier Quality Scorecard¶
Each supplier is evaluated quarterly based on:
| KPI | Weight | Calculation |
|---|---|---|
| Grade A delivery rate | 30% | % of deliveries achieving Grade A |
| Rejection rate | 25% | % of deliveries rejected |
| Average dry matter | 20% | Weighted average across all deliveries |
| Average reducing sugar | 15% | Weighted average across all deliveries |
| Documentation compliance | 10% | On-time/complete submission of field records |
Scorecard determines supplier tier (Platinum/Gold/Silver/Bronze) which affects contract renewal preference and volume allocation for the following season.
10.2 Right to Audit¶
Hongji Agriculture reserves the right to: - Audit any supplier's field operations, storage, and handling facilities with 48 hours' notice. - Take and analyze additional samples at any point in the supply chain (field, storage, transport). - Require corrective action plans for suppliers with chronic Grade B/C performance.
References¶
- ANSI/ASQ Z1.4-2008 (R2018): Sampling Procedures and Tables for Inspection by Attributes.
- United Nations Economic Commission for Europe (UNECE). 2020. Standard FFV-52 Concerning the Marketing and Commercial Quality Control of Potatoes.
- Codex Alimentarius. 2015. Standard for Fresh Potatoes (CXS 315-2015).
- Hongji Agriculture. 2025. Raw Material Procurement Contract — Standard Terms and Conditions.
- Chinese National Standard GB/T 8884-2017: Potato Starch and Related Processing Standards.
- Chinese National Standard NY/T 1063-2006: Grade and Specification for Processing Potato.
- USDA AMS. 2022. United States Standards for Grades of Potatoes for Processing. 7 CFR § 51.1540–1570.
- Pardo, J.E. et al. 2020. "Quality Parameters for Industrial Potato Processing." Journal of Food Science and Technology, 57(8): 2861–2872.
This document is part of the Hongji Agriculture (弘基农业) Technical Documentation Series. For more information about our vertically integrated potato supply chain — from seed breeding and cultivation to processing and global export — visit our official B2B website: https://hjpotatoflakes.com
Document maintained by the Hongji Agriculture Quality Assurance Division.
Next revision: July 2027