Nitrogen compounds in wine include proteins. Proteins contribute significantly to the concentration of nitrogen not digestible by yeasts in must and wine. They are the most common cause of clouding in white wines.
Protein clouding is a problem of serious economic importance for the production of wine as clarity is an important quality characteristic of wine. * The , identity, origin and factors influencing the formation of proteins associated with wine turbidities were examined by Hoj et al. (2000).
Most of the proteins synthesized in the rail are the same as those identified as being responsible for the formation of turbidity in white wines (Waters et al. 1996, 1998). · These proteins are stable at the pH of the wine and resist , proteolysis and therefore do not deteriorate during winemaking processes, thus adding to the nitrogen of the wine that is not digestible by the yeasts.
Their agglomeration during storage in the bottle can lead to the formation of blur.
The synthesis of proteins in the rail begins during overcrowding and their amount continues to increase as maturation progresses (Tattersall et al. 2011). 1997, Hoj et al. 2000, Pocock et al. 2000). · , the addition of nitrogen to the vine is expected to magnify the levels of the accumulated , protein as the rail matures , thereby increasing the undesirable content of non-digestible nitrogen from the yeasts and possibly the risk of clouding.
Only one study studied the effect of nitrogen addition in the vineyard on soluble must proteins (Spayd et al. 1994). The concentration of soluble proteins in wine from nitrogen-containing plants was 4.8 times higher compared to wines from plants to which no nitrogen was added. As a result of this, the demand for bentonite was increased by 6 times.
The estimation of the amount of nitrogen to be added to the vineyard should take into account the specific characteristics of the variety. ♪ For example , on the varietal rails ♪ Sauvignon blanc it accumulates about twice as much protein as on the cultivar's rails Sultana when both develop under the same conditions (Pocock et al. 2000).
In addition, 45-54% of the total content of proteins associated with blurs was found in the cortexes (Pocock et al. 1998). · Thus the addition of nitrogen to any white wine grape variety characterised by the accumulation of high concentrations of , proteins to which pre-fermentation extraction is applied and/or transported over long distances without special care , may increase the likelihood of fogging in the , bottle compared to a variety which accumulates lower protein concentrations.
· In conclusion ,, when adding nitrogen to the , vineyard, the winegrower should take into account the specific characteristics of each variety with regard to protein accumulation and implement strategies that minimise contact with the husks under inappropriate transport conditions (Sally-Jean Bell and Paul A. Henscke , 2005).
Source: Bell S-J and P.A. Henschke , 2005. Implications of nitrogen nutrition for grapes , fermentation and wine. Australian Journal of Grape and Wine Research 11 , 242-295
