Hazelnut Defect Types Explained: Shrivel, Mould, Stain & Industrial Quality Tolerances
Defect evaluation plays a critical role in hazelnut purchasing, quality assurance, roasting performance and final product consistency. This article explains each defect type, why it occurs, how processors classify it, and what tolerance levels are used in industrial specifications for chocolate, roasting and ingredient applications.
Why hazelnut defect classifications matter for buyers
Hazelnut defects directly influence flavor, roasting behavior, microbiological stability, visual appearance and industrial yield. For manufacturers in chocolate, bakery, roasting, cereal, snacking and paste production, understanding defect types is essential for building accurate specifications and ensuring consistent product quality.
Processors in Türkiye follow internationally recognized defect definitions, supported by optical sorting technology, manual inspection teams and laboratory analysis.
1. Shrivel (Underdeveloped Kernels)
Shrivel refers to kernels that are poorly developed, wrinkled or significantly smaller than expected for their caliber. These kernels have reduced oil content and inconsistent roasting behavior.
- Caused by insufficient fertilization, drought stress or immature harvesting.
- Negatively affects roasting uniformity and visible inclusions in chocolate.
- Typically included in the damaged kernel percentage in specifications.
2. Mould & Internal Rot
Mould is one of the most critical defects and a major risk factor for aflatoxin development. Moldy kernels often appear dark, brittle and have an off-flavor.
- Caused by high moisture during drying or storage.
- Strictly controlled through drying, sorting and laboratory testing.
- Completely unacceptable in premium lots; tolerance is near zero.
3. Skin Stain (Surface Discoloration)
Stain refers to dark or uneven coloring on the kernel surface without deeper quality defects. It is mainly aesthetic but important for visible applications.
- Often caused by weather exposure or enzymatic reactions.
- Does not significantly affect flavor.
- Tolerance varies depending on the customer: chocolate makers require stricter limits.
4. Broken & Mechanically Damaged Kernels
Broken pieces occur during cracking, sorting or transport. While acceptable in small amounts, excessive breakage reduces yield for whole-kernel applications.
- Measured separately from full defects.
- Important for pralines, dragée products and whole-nut chocolate bars.
- Often used as input for chopped formats instead of whole kernel sales.
5. Rancid or Oxidized Kernels
Rancidity results from lipid oxidation, often caused by poor storage, heat exposure or old crops. This defect negatively impacts flavor and is unacceptable for premium applications.
- Detected via sensory tests or peroxide value in lab analysis.
- Strongly influences paste, praline and chocolate flavor.
- Exporters avoid including old-season carryover in fresh-season lots.
6. Insect or Pest Damage
Pest-damaged kernels may contain boreholes, internal discoloration or hollow centers. Processors eliminate most of these through optical sorting and density separation.
- Closely linked to orchard management and harvest hygiene.
- Considered a serious quality and food safety defect.
- Specified as “damaged kernels” in industrial specifications.
7. Foreign Matter (FM)
Foreign matter includes any non-kernel material such as shell fragments, stones, twigs, or metal particles. Thanks to modern sorting lines, FM levels in Turkish exports are extremely low.
- Regulated strictly (FM tolerance: 0%).
- Controlled by sieves, aspirators, magnetic traps and optical sorters.
- Buyers should request metal detection before packing.
Typical industrial defect tolerances
Tolerance levels vary by buyer, but common ranges for high-quality Turkish hazelnut kernels include:
- Damaged kernels: 1–3%
- Shrivel: 0.5–2%
- Stained kernels: 1–4% depending on application
- Mouldy kernels: 0% tolerance
- Foreign matter: 0% tolerance
Buyers should always align specifications with their industrial process—especially for confectionery, roasting lines and paste production.
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