Improving food safety and quality in fruit sorting and grading with SWIR Imaging

Fruit and vegetable sorting has evolved far beyond surface-level inspection. As food safety regulations tighten and quality expectations rise, producers need inspection technologies that can detect internal defects, subtle material differences, and hidden contamination at full production speed. For example, supermarket customers are unlikely to purchase visibly bruised fruit such as apples, even when the internal quality remains suitable for consumption. With accurate sorting in place, these apples can be redirected to alternative uses such as juices, purees, or processed foods rather than being discarded, maximizing product value for retailers while significantly reducing food waste across the supply chain.

This is where Short-Wave Infrared (SWIR) imaging has become a game-changer.

Unlike visible or standard monochrome imaging, SWIR exploits the characteristic absorption behavior of water, sugars, fats, and organic compounds in the 1000–1700 nm wavelength range. These spectral properties make SWIR uniquely suited for identifying defects, foreign materials, and quality attributes that are invisible to conventional vision systems.

Below, we explore how SWIR cameras enable robust inspection across several high value produce categories.

Why SWIR for Food Sorting?

SWIR imaging provides three critical advantages in food inspection:

• Material discrimination: Different organic and inorganic materials absorb SWIR light differently, even if they look identical in visible light.
• Subsurface visibility: SWIR can reveal defects beneath skins or shells, especially in water-rich products.
• Reliable inspection of dark or low-contrast objects: black, brown, or dark surfaces remain inspectable in SWIR.

These properties make SWIR particularly effective for grading, defect detection, and foreign material identification.

Kiwi quality assessment

Detecting Blemishes, Soft Spots, and Puncture Damage

Kiwi fruit presents a unique inspection challenge: a rough, fibrous exterior that can mask internal damage. Visible inspection often fails to distinguish between cosmetic surface variation and true quality defects.

SWIR cameras enable:

• Blemish detection
  Internal bruising or tissue degradation alters moisture distribution within the fruit. SWIR wavelengths are highly sensitive to water absorption, making bruised regions appear with strong contrast.
• Soft spot identification
  Softening caused by over-ripening or internal breakdown results in localized moisture changes. These areas are difficult to identify using conventional visible-light inspection but become clearly distinguishable in SWIR images.
• Puncture and impact damage
  Small punctures or compression damage may not be obvious on the surface but lead to internal tissue disruption. SWIR reveals these hidden defects early, before decay progresses.
  

Citrus quality evaluation (Lemons &Oranges)

Going Beyond Surface Color

Citrus fruits are visually uniform, which makes detection particularly difficult using RGB or monochrome cameras alone. SWIR enables consistent detection of both surface and subsurface defects.

Key Defects Explained

• Blemishes
  Surface discolorations caused by mechanical damage or environmental stress. SWIR helps distinguish superficial marks from deeper tissue damage.
• Calyx issues
  The calyx is the green stem area. Missing, damaged, or decayed calyx regions can indicate reduced freshness or handling damage. SWIR improves contrast between healthy tissue and degraded areas.
• Rot
  Internal decay often begins beneath the peel. SWIR can detect moisture and tissue breakdown before rot becomes externally visible.
• Stalk damage
  Improper detachment can cause tearing and internal bruising around the stem area, which SWIR highlights clearly.
• Corrugations
  Wrinkling or uneven peel texture caused by dehydration or physiological stress. SWIR helps quantify severity by analyzing moisture distribution.
• Mold
  Early mold growth alters organic structure and moisture content. SWIR reveals mold-affected regions before visual spores appear.
• Oleocellosis (oil gland damage)
  Caused by mechanical pressure rupturing oil glands in the peel, leading to darkened scars. SWIR enhances contrast between healthy and oil-damaged areas.
• Punctures
  Small penetrations can trigger rapid decay. SWIR detects internal damage associated with these punctures, even if the surface opening is minimal.

Dried Fruit quality control

Foreign Material Detection and Quality Assurance

Dried fruits present a different challenge: low moisture content and highly variable shapes and textures. Traditional visible inspection struggles to reliably detect dense contaminants.

SWIR excels at:

• Foreign material detection
  Dense inorganic contaminants such as:
  • Rocks
  • Glass
  • Metal fragments
• Skin damage and structural defects
  Tears, splits, or excessive dehydration alter internal structure, which SWIR highlights through contrast changes.
• Mold detection
  Mold growth changes both chemical composition and moisture content. SWIR enables early detection, even on dark dried fruits like raisins or figs.

These materials have distinctly different SWIR absorption characteristics compared to organic dried fruit, making them stand out clearly—even when similar in color.

Nut quality sorting

From Foreign Materials to Aflatoxin Risk Reduction

Nut quality sorting requires reliable differentiation between acceptable product and defects based on internal structure and material composition rather than surface appearance.

Key SWIR Capabilities

• Foreign material identification
  SWIR reliably detects stones, shells, and other non-nut materials mixed into product streams.
  
  
• In-shell nut detection
  In-shell almonds or other nuts can pass unnoticed in visible inspection. SWIR differentiates shell material from kernel tissue with high reliability.
• Insect damage
  Internal infestation alters fat and moisture distribution, producing clear contrast in SWIR images.
• Rotten and split nuts
  Internal decay or structural fractures change absorption characteristics, making defective nuts easy to isolate.