The effect of Nitrogen and Sulphur foliar applications in hot climates

In addition to aroma compounds also protein composition strongly influences the quality of wines. Proteins of wine derive mainly from the plant Vitis vinifera and may be influenced by abiotic stress as well as fermentation conditions or fining. Additionally, fungal infections can affect the protein content as well by introducing fungal proteins or affecting grape protein composition. An infection of the vine with the plant pathogenic fungus Botrytis (B.) cinerea was shown to cause a degradation of proteins in the resulting wine. Moreover, it influences the foaming properties in sparkling wine.

Around the world, the alcohol content of wine has been steadily increasing; partly as a consequence of climate change, but also due to improvements in viticultural management practices and winemaking techniques [1,2]. Concurrently, market demand for wines with lower alcohol levels has increased as consumers seek to reduce alcohol intake for social and/or health reasons [3]. As such, there is increasing demand for both innovative methods that allow winemakers to produce ‘reduced alcohol wines’ (RAW) and a better understanding of the impact of such methods on the composition of RAW. This study therefore aimed to investigate compositional changes in two red wines resulting from partial alcohol removal following treatment by one such method, involving a combination of reverse osmosis and evaporative perstraction (RO-EP).

Wooden barrels have been the preferred method for oak maturation for wines, but the use of alternative oak products, such as staves and oak chips have increased in South Africa due to lower production costs. This study investigated the effect of different oak products used during fermentation and ageing on the sensory profile, degree of liking and perceived quality of a South African Chenin blanc wine. The different wine treatments included an unoaked tank control wine, wines matured in 5th fill barrels, wines matured in new barrels from three different cooperages, and wines matured in 5th fill barrels with stave inserts from two different cooperages.

Maturation of wine on lees (often referred as sur lie) is a common practice applied by many winemakers around the world. In the past this method was applied mainly on white and/or sparkling wine production but recently also to red wine production. In our experiment, we matured red wine on wine lees of two origins: a) Light wine lees, collected after the completion of the alcoholic fermentation, b) Heavy lees, collected after the completion of the malolactic fermentation. The lees were free of off-odors and were added in the red wine in percentage 3% and 8%, simulating common winemaking addition. The maturation lasted in total six months and samples were collected for analysis after one, three and six months. During storage the lees were stirred.

Fermentation derived sulfidic off-odors due to hydrogen sulfide (H2S) and low molecular weight thiols are commonly encountered in wine production and removed by Cu(II) fining. However, the mechanism underlying Cu(II) fining remains poorly understood, and generally results in increased Cu concentration that lead to deleterious reactions in finished wine. The present study describes a mechanistic investigation of the iron and copper mediated reaction of H2S, cysteine, 3-sulfanylhexan-1-ol, and 6-sulfanylhexan-1-ol with oxygen. The concentrations of H2S, thiols, oxygen, and acetaldehyde were monitored over time. It was found that Cu(II) was rapidly reduced by both H2S and thiols to Cu(I).