WINETECH Technical Yearbook 2019

NON-VOLATILES IN GRAPES AND MUST The analyses took place at various stages of the winemaking as indicated in Figure 2. The compounds selected for evaluation were the ones potentially affected by the treatments applied (S- and N-containing compounds): Yeast Assimilable Nitrogen (YAN) in both its aspects, ammonia and Free Amino Acids (FAN) and glutathione (GSH) for the grapes and must. In wine, major volatiles (affected indirectly through amino acid composition at the must stage), methoxypyrazines and thiols were evaluated. These results will be presented in Part 3 of the series. As expected, the different foliar fertilisation applications had an effect on the non- volatile content of the juices and musts. Generally, the composition and levels found were in agreement with the findings of the few published foliar fertilisation reports (Juhasz, 2015; Gutiérrez-Gamboa et al ., 2017; Lasa et al ., 2012; Lacroux et al ., 2008). The differences between the treatments were sometimes significant and at other times minimal, but trends were observed with certain non-volatile compounds. The oenological parameters were generally not affected by the treatments, so we decided not to include the results in this article. YAN In this study, nitrogen foliar fertilisations (N and N+S) positively increased the YAN levels compared to the control and these

Buffer 3 vines Buffer 3 vines Buffer 3 vines Buffer 3 vines

S

Buffer 3 vines Buffer 3 vines Buffer 3 vines Buffer 3 vines

C

Buffer 3 vines Buffer 3 vines Buffer 3 vines Buffer 3 vines

N

Buffer 3 vines Buffer 3 vines Buffer 3 vines Buffer 3 vines

N+S

Buffer 3 vines Buffer 3 vines Buffer 3 vines Buffer

12 vines

12 vines

12 vines

12 vines

N+S

S

C

N

12 vines

12 vines

12 vines

12 vines

N

N+S

S

C

12 vines

12 vines

12 vines

12 vines

C

N

N+S

S

12 vines 3 vines FIGURE 1. Experimental layouts used in the project, indicating the number of vines used for each treatment and the buffer zone used between the treatments. 12 vines 12 vines 12 vines

Crush and destem

Racked juice

Finished AF

3 months aged wine

Finished PS & CS

9 months aged wine

Bottling

pH, TA, ˚B

pH, TA, ˚B

Free SO 2

GSH

pH, TA

Sensory

Sensory

Free SO 2

Ethanol %

Free SO 2

pH, TA, Et %

pH, TA, Et %

Residual sugar

Volatile thiols Major volatiles

Volatile thiols Major volatiles

YAN

GSH

GSH

Methoxy- pyrazines*

FIGURE 2. Schematic representation of the winemaking process and the stages sampled for analyses (AF: alcoholic fermentation, PS: protein stabilisation, CS: cold stabilisation).