Incoming Inspection — Raw Potato Receiving QC¶
The quality of finished French fries is largely determined before the first potato enters the processing line. Incoming inspection is the first and most important quality gate in the entire production process.
Raw Potato Specifications at Receiving¶
| Parameter | Target | Rejection Threshold | Test Method |
|---|---|---|---|
| Dry matter (DM) | ≥22% | <20% | Underwater weight method (specific gravity) |
| Reducing sugars (combined glucose + fructose) | <0.25% | >0.35% | DNS method or YSI analyzer |
| Tuber diameter | 50–85 mm | <40 mm or >100 mm | Caliper / ring gauge |
| Tuber length | ≥65 mm | <50 mm for >10% of load | Measured sample |
| External defects (rot, green, mechanical damage) | ≤3% by weight | >5% | Visual inspection, hand grading |
| Soil / foreign matter | ≤1% by weight | >3% | Weight after washing |
| Internal defects (hollow heart, internal necrosis) | ≤2% by count | >5% | Cut-test on representative sample |
| Black spot bruise | ≤5% by count | >10% | Sample cut + 24hr observation |
| Variety purity | ≥95% | <90% | Visual variety identification |
Sampling Protocol¶
Lot Sampling¶
| Lot Size (tonnes) | Number of Samples | Sample Size per Point |
|---|---|---|
| <20 | 5 points | 10 kg per point |
| 20–50 | 8 points | 10 kg per point |
| 50–100 | 12 points | 10 kg per point |
| >100 | 15 points | 10 kg per point |
Key Insight: Sampling must follow a systematic pattern, not a convenience sample. For truckloads, take samples from at least 5 different positions (front, middle, rear, left, right) at two depths (top 50 cm and mid-level). Surface-only sampling will over-represent quality.
Sampling Procedure¶
- Truck arrival — Record truck number, supplier name, variety, harvest date, field location
- Documentation — Verify supplier COA, pesticide use records, variety certificate
- Visual inspection — Observe for free water (wet load — potential disease), large clods, foreign material
- Temperature check — Pulp temperature of representative tubers (target: 7–15°C)
- Sample extraction — Systematic grid sampling as above
- Lab analysis — DM, sugars, size grading, defect count
Dry Matter Testing — Underwater Weight Method¶
Since DM is the single most important quality parameter, it must be tested accurately at receiving.
Procedure¶
- Take a clean 5 kg representative sample of well-washed tubers
- Weigh the sample in air (Wair)
- Submerge the sample in water and weigh underwater (Wwater)
- Calculate specific gravity (SG):
SG = Wair ÷ (Wair − Wwater) - Estimate DM from SG:
DM% ≈ 209.81 − (188.22 ÷ SG)
Key Insight: The underwater weight method is fast, requires no chemicals, and is accurate to ±0.5% DM when properly executed. It can be performed at receiving within 5 minutes per lot. Many facilities that skip this step at receiving end up processing suboptimal raw material and compensating with processing adjustments — which rarely fully recovers the quality lost.
Reference Table — Specific Gravity to DM¶
| Specific Gravity | Estimated DM% | Suitability for Processing |
|---|---|---|
| 1.075 | 19.0% | ❌ Poor — high oil absorption expected |
| 1.080 | 20.4% | ⚠️ Marginal — accept only if supply tight |
| 1.085 | 21.5% | ✅ Acceptable — meets minimum |
| 1.090 | 22.5% | ✅ Good — Dinweys target |
| 1.095 | 23.4% | ✅ Excellent |
| 1.100 | 24.2% | ✅ Premium |
Reducing Sugar Testing at Receiving¶
Colorimetric (DNS) Method¶
- Reagent preparation: Dinitrosalicylic acid (DNS) reagent
- Sample preparation: Potato strips homogenized, centrifuged, supernatant filtered
- Reaction: Heat with DNS reagent at 100°C for 5 minutes
- Measurement: Absorbance at 540 nm, compared to glucose standard curve
- Result: Combined glucose + fructose, reported as % reducing sugars
Rapid YSI / Biochemistry Analyzer Method¶
For faster turnaround, Dinweys uses a YSI 2900 biochemistry analyzer:
| Feature | Details |
|---|---|
| Sample prep time | 3 min (mash + filter) |
| Analysis time | 60 seconds per sample |
| Glucose + Fructose | Measured separately |
| Accuracy | ±0.01% |
| Throughput | 30+ samples per hour |
Size Grading at Intake¶
Tuber size distribution affects cutting yield significantly. Oversized tubers cause cutter jams; undersized tubers produce too many short strips.
| Size Class | Diameter | Length | Processing Suitability |
|---|---|---|---|
| Small | <45 mm | <50 mm | ❌ Low fry yield — many short strips |
| Medium | 45–65 mm | 50–75 mm | ✅ Good for 7–9mm cuts |
| Large | 65–85 mm | 75–100 mm | ✅ Optimal for all cuts — highest strip yield |
| Extra large | >85 mm | >100 mm | ⚠️ May require size reduction — possible cutter issues |
Size Grade Distribution Target at Receiving¶
| Size Class | Target Percentage |
|---|---|
| Small (<45 mm) | ≤5% |
| Medium (45–65 mm) | 30–40% |
| Large (65–85 mm) | 50–60% |
| Extra large (>85 mm) | ≤5% |
Key Insight: The "yield" of usable cut strips from a tuber is a function of both its length and shape. Long, blocky tubers of 65–85 mm diameter give the highest strip yield. Long, narrow tubers give lower yield. Round tubers are the worst for straight-cut processing — they produce many short end-strips and odd-shaped pieces.
Rejection Protocol¶
If raw material fails any of the following, the load should be quarantined and evaluated:
| Condition | Action |
|---|---|
| DM <20% | Reject entire load — not suitable for processing |
| Reducing sugars >0.35% | Reject — will produce dark fries even with adjusted processing |
| Rot / decay >5% by weight | Reject — high mold risk, potential mycotoxin issues |
| Frozen tubers (pulp temp <2°C) | Reject — low temperature will cause sugar spike and processing difficulties |
| Mixed variety (composition <90% target variety) | Accept with discount or segregate — process separately |
Partial acceptance may be considered for borderline cases with documented supplier agreement and adjusted pricing.
Incoming Inspection Record-Keeping¶
| Record | Data Fields | Retention |
|---|---|---|
| Receiving report | Date, supplier, variety, truck #, weight, DM, sugars, defects | 3 years |
| Supplier scorecard | Cumulative DM average, sugar stability, defect rate | Ongoing |
| Season summary | Average DM by variety, by field, by harvest date | 5 years |
| Rejection log | Rejection reason, supplier, action taken | 5 years |