A recent trial conducted in the Barossa valley of Australia revealed that nitrogen and sulphur foliar sprays can have significant effects on Chardonnay and Shiraz aromas, and it is not necessarily all that positive. In the case of Chardonnay, the sprays led to an increase in grapefruit and passionfruit aromas. The former being a positive, but the latter (the result from the higher dosage regimes) is not an aroma necessarily associated with Chardonnay, but rather with Sauvignon blanc.
In the case of the Shiraz, higher dosage regimes led to what was described by the panellists as a “drain” character. This was their descriptor for “unpleasant, reductive, sulphide-related notes.” One would question why the attempt was made on Shiraz in the first place? Well, the quest was rather noble in that it has been demonstrated through research in France and South Africa that nitrogen and sulphur foliar sprays increase volatile thiol concentrations in wines. It has also been demonstrated in South Africa and Australia that red wines can contain volatile thiol concentrations above their sensory thresholds, and that these thiols can positively contribute to the “blackcurrant” aroma. Since blackcurrant is often used as a descriptor for Shiraz aroma, the effect of the sprays on the cultivar was therefore investigated.
The Australian trial, that was based on French research, also revealed some other interesting results, such as increased YAN (ammonia and amino acids) in musts, and in the case of the Shiraz grapes, there was some evidence of a sulphur burn in the high treatment vines, which is also a phenomenon to keep in mind when designing future related research projects.
Winetech funded research in South Africa, conducted a few years ago by Dr Astrid Buica, confirmed significant increases in volatile thiol concentrations in Sauvignon blanc and Chenin blanc wines when nitrogen and sulphur foliar sprays were applied on vines pre-harvest. However, even though the chemistry said one thing, the formal sensory analysis said a different thing, in that no significant differences were detected by the panellists between the treated and untreated wines. So basically, no point to go through the trouble and cost of treating the vines if nobody is going to notice a difference.
Both these studies were limited studies. Both demonstrated, however, that there is an effect and that it can potentially be positive. It’s a question of finding the proverbial “sweet spot” with the right grapes, the right climate, the right time of application and the right dosage. Winemakers are encouraged not to give up hope on this line of research, since the end game could potentially be very positive. In the voice of researchers around the world: “More research is needed.”
Josh Hixson and co-workers. Enhancing tropical fruit flavour in Chardonnay and Shiraz through foliar nutrient sprays. Wine and Viticultural Journal, Winter 2020.
Astrid Buica and co-workers. Nitrogen and sulphur foliar fertilisation, Parts 1-3. WineLand Magazine, Aug, Sep, Oct 2019.
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