Quick diagnosis: Browning is usually oxidation and bruising rather than spoilage by itself. Flavour and storage history determine whether it remains usable.
What the Symptoms Tell You
Bright herbs become olive or grey, especially on the exposed surface, while aroma may fade.
Why This Usually Happens
The most common causes are connected to temperature, ratio, timing, ingredient condition or technique. Compare the dish with these specific checks:
- Herbs were warm, wet or heavily bruised.
- Blending generated heat and incorporated too much air.
- The pesto remained exposed to oxygen.
Professional Rescue Method
- Cool the pesto quickly and press clean covering directly against the surface.
- Refresh only mild discoloration with reserved fresh herbs and appropriate acid.
- Use browned but safely stored pesto in a cooked application when appearance is unacceptable raw.
Safety and Quality Limit
Discard pesto with mould, gas, sour spoilage odour or unsafe storage. Never scrape mould from a soft sauce and serve the remainder.
Prevent It Next Time
- Dry herbs thoroughly and chill equipment when useful.
- Pulse briefly instead of blending continuously.
- Store in a clean small container with minimal headspace.
Chef’s Verification Test
Spread a teaspoon thinly on a white plate and smell it; colour may be darker, but aroma should remain fresh and clean.
Use this guide as general culinary education. Follow local food-safety rules, allergen controls and equipment manufacturer instructions.