6. Special Inspection Procedures
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6.1 Method of Cutting to Determine Waste
In determining the amount of waste required to remove a defect, the recommended procedure is to first make a straight cut about 6 mm (¼ inch) deep across the potato to remove all or most of the damage. If the damage is still present, then a curved or half-moon cut should be made. The amount removed by both the straight cut and curved cut should be used to determine waste. The above method is probably not practical or fair in assessing "damage" on the flat side of a potato. In these instances only, a curved or half-moon cut should be used to remove the defect.
Offices are supplied with scales to assess "cut-off" damage. Inspectors should frequently practice making 5% and 10% "cut-offs" so that their judgement in assessing "damage" and "serious damage" will be uniform and accurate.
6.2 Procedure for Sampling for Internal Defects
6.2.1 Preliminary Examination
Potatoes are subject to having internal defects, for example, net necrosis, hollow heart, etc. Some of these defects may give an external indication of problems, but some do not. Therefore, in order to confirm that there are no internal defects present, the inspector should always make a preliminary examination by cutting some randomly selected specimens from the first three samples examined.
When the inspector is satisfied that there are no internal defects in the samples, the inspector does not need to cut any more specimens. If the preliminary examination shows internal defects are present, the inspector must decide if the external appearance is a reliable indicator of the internal defect or if the defect is hidden. This will dictate which of the following two methods to use to inspect for internal defects.
6.2.2 Sampling Method for Internal Defects that Have No External Indications (Composite)
When the preliminary examination confirms that there are hidden internal defects where the outward appearance gives no indication of the defect or is not reliable, the inspector should take random samples by selecting a predetermined weight of specimens from each package. The samples are then cut and defective specimens found must be scored against the cut sample only.
For example, when inspecting a 22.7 kg (50 lb) bag of potatoes, the inspector finds that internal discolouration is present but the outward appearance of the specimens gives no indication of the defect. The inspector then takes 4.5 kg (10 lb) from the bag completely at random and, after cutting every specimen, finds that .9 kg (2 lb) are showing internal discolouration.
The .9 kg (2 lb) of internal discolouration would be scored against the 4.5 kg (10 lb) sample (2÷10 × 100 = 20% ). The sample to be cut must be selected completely at random and the size of the sample must be accurate and consistent from each bag. The remaining 18.2 kg (40 lb) are used exclusively for scoring size, grade and condition defects. Never score the same specimen twice.
It is acceptable to either cut the 4.5 kg (10 lb) sample and score it as each package is inspected, or the 4.5 kg (10 lb) from each sample may be set aside and accumulated for inspection as a composite sample after the other samples are inspected.
However, on the certificate, no ranges shall be reported on a composite sample.
6.2.3 Sampling Method for Internal Defects that have External Indications
If the outward appearance of the specimen does give some indication of the defect, the inspector should select the suspect specimens from the total sample and cut them for examination. Those specimens found to be defective must be scored against the total sample. For example, if a preliminary examination of a 22.7 kg (50 lb) bag of potatoes reveals that only the larger rough potatoes have hollow heart, this type of potato is picked out of the lot and cut for examination.
If 4.5 kg (10 lb) are picked out of a 22.7 kg (50 lb) bag and, after cutting every specimen, 2.3 kg (5 lb) are scoreable for hollow heart, then the 2.3 kg (5 lb) are scored against the total 22.7 kg (50 lb) sample. (5÷50 × 100 = 10% ). In this method, internal defects are to be reported on the certificate showing range.
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