Preserving the sensory profile of wine over time is one of the most complex challenges in contemporary oenology. Today, this need must be addressed alongside the growing use of clear glass packaging to enhance the colour characteristics of rosé and white wines. However, exposure to light radiation activates specific degradation processes, leading to the development of the defect known as light-struck taste, or LST.
This alteration leads to the development of sulphurous notes, such as cooked cabbage, garlic and onion, as well as the loss of fruity descriptors and the wine’s original freshness.
The biochemical mechanisms of light-induced alteration
The phenomenon of light-struck taste is governed by a precise photochemical sequence mediated by riboflavin, also known as vitamin B2.
The process develops through a sequence of photochemical reactions:
- Photosensitisation: riboflavin absorbs light radiation in the spectrum between 370 and 450 nm, entering an excited state.
- Substrate oxidation: in its excited state, the molecule oxidises methionine, a sulphur-containing amino acid naturally present in the medium.
- Formation of sulphur compounds: the reaction triggers the formation of methanethiol and dimethyl disulphide, the main compounds responsible for the development of light-struck taste.
- Kinetic efficiency: the catalytic activity of riboflavin is extremely high; a single riboflavin molecule can photo-oxidise up to 20 methionine molecules. This makes the wine matrix unstable even when exposed to light for only short periods.
Light Seven Stress: technology and operating principle
To transform photochemical susceptibility from an unknown factor into a quantifiable analytical parameter before bottling, Ever developed Light Seven Stress (L7S), a patented portable instrument designed for the predictive determination of light-related shelf life.
Unlike traditional empirical tests, the system is based on a high-intensity RGB LED matrix — red, green and blue. This technology makes it possible to modulate 7 different light spectra, simulating the exposure of wine on retail shelves — fluorescent light over several months — according to the specific wine matrix.
Thermal decoupling
A critical factor in traditional irradiation tests is heat interference, which overlays thermal ageing kinetics onto purely photochemical processes. The L7S device isolates the light variable through three measures:
- Passive dissipation: structure made of aluminium with high thermal conductivity.
- Physical insulation: separation of the irradiated samples using transparent plates.
- Active temperature control: optional temperature control through the insertion of eutectic plates.
Operating protocol and correlation metrics
The analytical method takes only a few minutes and can be easily integrated into the winery’s quality control activities:
- Sampling: 40 mL of wine are collected and transferred into airtight clear glass vials.
- Insertion: the vials are placed in the chamber of the L7S instrument.
- Stress cycle: the instrument is activated for an interval of between 10 and 20 minutes, with a standard reference time set at 15 minutes.
- Evaluation: at the end of the cycle, the sample undergoes a new organoleptic and analytical assessment.
Correlation of analytical and predictive parameters
The main operating parameters of the test are reported in the following table.
Biotechnological and winery strategies for prevention
Risk-level quantification through L7S allows the winemaker to establish targeted stabilisation protocols based on synergistic interventions.
1. Use of tannins
Some tannins have a lower oxidation potential than methionine, meaning they release electrons more easily, and stabilise any mercaptans already formed by creating stable chemical bonds. In this context, the formulations EVERTANN BLANCHE CRU, EVERTANN FRUITY CRU, BLUETANN ALLEGRO and BLUETANN VIVACE are technically applicable.
2. Antioxidant treatments and selective adsorbents
- Reduction of the sensitive fraction: the application of active oenological carbons makes it possible to reduce the concentration of riboflavin by up to 70%. This operation requires carefully balanced dosages in order to preserve the aromatic fraction of the matrix.
- Selective clarification: for more targeted interventions that are respectful of the wine’s structure, complex processing aids such as EVERCLAR GAMMA or CYTOCLAR are used.
- Redox potential management: maintaining adequate levels of sulphur dioxide — around 50 mg/L — is essential to block unstable intermediates such as methional, preventing their subsequent transition into malodorous volatile molecules.
3. Packaging validation
The objective data obtained from the L7S test guide the choice of the optimal container. For wines that are more sensitive to light-struck taste, the use of amber glass is necessary, as it can shield almost all critical wavelengths. Conversely, a stability result in the L7S test allows bottling in clear or green glass to be planned, supported by precise scientific validation.
Conclusions
The use of the Light Seven Stress system makes it possible to manage the risk of light-struck taste through an objective and predictive approach. Thanks to a rapid test that can be easily integrated into laboratory activities, the winemaker can assess the wine’s photochemical stability in advance, verify the effectiveness of the treatments applied and support decisions regarding ageing and packaging selection with objective data. This system helps reduce the risk of post-bottling defects and preserve the wine’s sensory profile over time.
For further technical information and application support:
* Web: www.ever.it * Phone: 0421 200455 * E-mail: info@ever.it
