Fermentation rate in White Riesling (Vitis vinifera L.) grape juice as
affected by vineyard nitrogen fertilization
Marko Karoglan1, Luna Maslov1, Ana Jeromel1, Mirela Osrečak1, Bernard Kozina1, Josip
Marijanović2
Agronomski fakultet, Sveučilište u Zagrebu, Zavod za vinogradarstvo i vinarstvo, Svetošimunska
cesta 25, Zagreb ([email protected])
2
student Agronomskog fakulteta u Zagrebu
1
Summary
Nitrogen (N) fertilizer (urea) was applied by hand to vineyard of White Riesling grapes at
rates of 0, 23, 70 or 117 kg N/ha/year from 2006 to 2009. Fermentation rate increased with
increasing N fertilization, although only one of four juices from 0 kg N/ha completed
fermentation, while only two of four 23 kg N/ha completed fermentation. All juices from 70
and 117 kg N/ha completed fermentation, but fermentation rate was unecceptable slow. Long
fermentation time was strongly correlated with low free amino nitrogen levels in all juices,
varying from 13 to 40 mg/L. Nitrogen fertilization rate affected higher titratable acidity.
Key words: fermentation rate, fertilization, grape juice, nitrogen
Introduction
It is well known that nitrogen (N) is required by yeast for growth and completion of alcoholic
fermentation in grape juice (Bisson, 1991). Sluggish or stuck fermentations may result from
nitrogen deficiencies of grape juice (Bell et al., 1979; Ingledew and Kunkee, 1985). Many
producers utilize to fertilize the vineyard to avoid this problems, although this does not always
assure sufficient content of nitrogen compounds in the grape (Bell and Henschke, 2005).
Agenbach (1977) reported that concentrations greater than 140 mg/L of assimilable nitrogen
were required for sufficient yeast growth to complete fermentation. Free amino nitrogen
(FAN) content has been used as an indicator of total avaliable nitrogen in juice (Amerine and
Ough, 1980), although chemical determinations of FAN do not discriminate between those
free amino nitrogen containing compounds that can be utilized by Saccharomyces cerevisae
for thier nitrogen content and those that cannot.
Concentration of nitrogenous compounds in grape juice is influenced by viticultural practice
such as vineyard nitrogen fertilization (Agenbach, 1977; Bell et al., 1979), cultivar (Huang
and Ough, 1989), rootstock (Huang and Ough, 1989) and growing season (Spayd et al., 1994).
Many studies examined the impact of vineyard nitrogen fertilization on the fermentation
kinetics (Agenbach, 1977; Bell et al., 1979). Overall fermentation rate is lineary related to
must total nitrogen. Application of N fertilizer to Thompson Seedless grapevines increased
fermentation rate of juices which was found to be related to must total N concentration (Bell
et al., 1979). Pre-harvest application of N fertilizer increased juice total N concentration, and
fermentation time to dryness decreased lineary as the total N concentration in juice increased.
However, this viticultural practice could create some problems as the high vineyard nitrogen
application can result in reduced grape colour and total soluble solids concentration.
Difficult fermentations of Riesling musts in north-western region of Croatia are fairly
frequent. Spayd et al. (1994) reported that N concentration in Riesling juice are increased by
even moderate (56 kg N/ha) applications of N fertilizer. The purpose of this study was to
investigate the impact of the N fertilizer applications on fermentation rate in Riesling must.
Materials and methods
Research was laid out during four growing seasons (2006-2009). Grape harvest as well as
vinification process happened in the experimental field of Department of enology and
viticulture, Faculty of Agriculture in Zagreb, which is placed on the hills near Zagreb. The
White Riesling grapevines were grafted on Vitis Berlandieri x Vitis Riparia SO4 rootstock.
Nitrogen application rates were 0, 23, 70 or 117 kg N/ha and were replicated three times in
the filed using a randomized complete block design. Each treatment comprised 36 grapevines,
so there were total 124 White Riesling grapevines included in the experiment.
Vines were spaced 1.2 m apart within rows and 2.1 m apart between rows. Nitrogen in the
form of urea was applied by hand within 30-cm band on each side of each experimental row.
Fertilizer application were made in spring, immediately after bloom.
The fruits were harvested according to usual technological ripeness, and before harvest the
vines were berry-sampled several times to determine maturity. Each replication was destemed
and crushed separately, and immediately pressed. The juice was collected in 25-L glass
containers, SO2 added and the juice settled per 24 hours. The samples of must were taken and
analyzed before fermentation started. The musts were analyzed for total acidity and sugar
content according to the official O.I.V. methods (2001). Free amino nitrogen (FAN) content
was determined according to the NOPA procedure (Butzke and Dukes, 1998)
The clear juice was racked from the lees, yeast inoculum of Saccharomyces cervisiae 228B
was added, and the must was fermented at 16°C.
Fermentation progress was determined by measuring changes in sugar content. Fermentation
rate were determined as days for the must to ferment to <1 g/L of residual sugar. Data were
analyzed by ANOVA, with nitrogen fertilization rate as variability source.
Results and discussion
Must composition at harvest: Nitrogen fertilization didn't delayed fruit maturation regarding
soluble solids content (Table 1). Moreover, the sugar content increased when nitrogen
fertilizer was applied. In 2006 and 2009 the sugar content was the lowest in control musts,
without nitrogen fertilization. Fertilization with 23 kg N/ha influenced the highest must sugar
content in three of four experimental years, but statistical significance showed up only in 2006
and 2009 years.
Peacock et al. (1991) stated that nitrogen fertilization generally influenced lower sugar
content in grape must. Christensen et al. (1994) also found that fertilization with 112 kg N/ha
reduced sugar content in grape juice. But there are also authors finding no differences in grape
sugar content due to rate of nitrogen fertilization (Bell et al., 1979).
Nitrogen fertilization rate affected higher titratable acidity (TA). The lowest content of
titratable acidity was found in control musts in all growing seasons, but only in 2006 with
statistical significancy.
Bell et al. (1979) reported that total acidity increased significantly with increasing nitrogen
fertilization. The explanation is the probable increase in vine vigor and leaf surface area due
to increasing nitrogen fertilization. So, there is an increased production of acids in leaves and
subsequent translocation to the grapes. The increased acidity may be due also to the denser
leaf canopy that accompanied nitrogen fertilization, resulting in greater shading of fruit and
lower fruit temperature than on unfertilized vines. Christensen et al. (1994) investigated
nitrogen fertilization among 4 cultivars, and reported higher total acidity content but only in
Grenache and Chenin blanc juices. According to Bavaresco et al. (2001) nitrogen fertilization
affected higher acidity content, but without significant statistical differences.
Table 1. Effect of nitrogen fertilization rate on sugar content of White Riesling grape juice,
2006-2009.
kgN/ha
0
23
70
117
2006
95.7
104.7
100.7
103.3
2007
88.3
90.3
87.7
88.3
2008
99.7
100.0
98.7
100.7
2009
86.3
92.0
89.0
87.7
92.5
96.8
94.0
95.0
Table 2. Effect of nitrogen fertilization rate on total acidity of White Riesling grape juice,
2006-2009.
kgN/ha
0
23
70
117
2006
10.15
13.63
13.40
11.17
2007
8.66
8.92
9.43
9.57
2008
7.17
7.31
7.35
7.20
2009
8.97
8.98
9.36
9.26
8.74
9.71
9.89
9.30
Free amino nitrogen (FAN): In all four years, when compared with no N fertilization, juice
FAN concentrations were higher when N fertilizer was applied, esspecially rates of 70 and
117 kg N/ha (Table 2). Statistical significant differences were observed in all years except
2007. Linear increase in FAN concentration with increasing N fertilization was detected only
in 2009 year. In the other three growing seasons fertilization with 117 kg N/ha had no
significant effect compared with 70 kg N/ha.
However, Spayd et al. (1994) found that juice FAN concentration at least doubled when 56 kg
N/ha were aplied to the vines, and increased lineary till maximum fertilization rate of 224 kg
N/ha.
It is also worth to note that the FAN concentrations in this investigation are significantly
lower than those recommended for completion of alcoholic fermentation. Several authors
(Agenbach, 1977; Ingledew and Kunkee, 1985) found that the level of 140 mg N/L (meaning
yeast assimilable nitrogen (YAN), that can be assimilated by wine yeasts) is necessary for
completion of alcoholic fermentation. Spayd et al. (1996) examined 142 must samples of
White Riesling from Washington state, and found an average of 156 mg/L of FAN. The same
authors stated that in 96% samples of White Riesling was found less than 400 mg/L of FAN,
and in 77% samples even less than 200 mg/l, claiming that White Riesling among all white
cultivars had the lowest FAN concentration in must.
When comparing with our results it is obvious that the FAN content in White Riesling musts
is significantly lower, and far away from recommended and necessary concentrations for good
alcoholic fermentation.
Table 3. Effect of rate of nitrogen fertilization on free amino nitrogen in must (mg/L) of
White Riesling, 2006-2009.
kg N/ha
0
23
70
117
2006
13.22
23.92
29,02
21,79
2007
24,05
25,58
34,28
30,92
2008
27,23
30,11
40,52
37,25
2009
14,51
18,95
19,03
22,57
19,75
24,64
30,71
28,13
Fermentation rates: The effect of nitrogen fertilization is shown in Figures 1-4. It is obvious
that only in 2007 all must completed fermentation to dryness, with 70 and 117 kg N/ha in 29
days, and 0 and 23 kg N/ha in 37 days. That was the only year in which control treatment
(without N fertilization) completed fermentation. Must treated with 23 kg N/ha completed
fermentation only in 2006 and 2007 years, while 70 and 117 kg N/ha completed fermentations
in all experimental years. Average number of days needed for completing fermentation for 70
and 117 kg N/ha treatments was 32 and 34 days respectively, which can be considered as a
quite long term fermentation. Other two treatments showed no capability for completing
fermentation, which was prolonged for even 52 or 56 days, and stuck with 6-8 g/L of residual
sugar.
The length of fermentation time is not strongly related to the FAN level in the juice,
especially when looking year by year FAN levels. The explanation is in fact that FAN as a
chemical definition do not discriminate between those free amino nitrogen containing
compounds that can be utilized by Saccharomyces cerevisae for their nitrogen content and
those that cannot.
Graf 1. Fermentation rate, White Riesling, 2006
Graf 2. Fermentation rate, White Riesling, 2007.
300
250
250
200
200
150
0
g/L
23
150
0
g/L
23
70
70
117
117
100
100
50
50
0
0
28.09.
5.10.
11.10.
17.10.
23.10.
30.10.
2.11.
6.11.
10.11.
15.11.
19.11.
12.09.
22.11.
24.09.
Graf 3. Fermentation rate, White Riesling, 2008.
3.10.
11.10.
16.10.
19.10.
Graf 4. Fermentation rate, White Riesling, 2009.
250
250
200
200
150
150
0
g/L
23
0
g/L
23
70
70
117
117
100
100
50
50
0
0
16.10.
20.10.
26.10.
3.11.
10.11.
15.11.
21.11.
27.11.
2.12.
7.12.
12.12.
5.10.
9.10.
12.10.
21.10.
30.10.
4.11.
9.11.
13.11.
Conclusions
Nitrogen fertilization delayed fruit maturity as indicated by total acidity concentrations. The
impact of nitrogen fertilization on FAN concentration varied from year to year, but was higher
in fertilization treatments. In fact, in all treatments the FAN concentrations were extremely
low, that can not assure adequate conditions for completing alcoholic fermentations in the
appropriate time. Application of sufficient N fertilizer in the soil immediately after bloom,
and in form of urea to assure complete fermentation of White Riesling juice produced from
Zagreb vineyard hills is not possible, especially when considering very high partitioning of
clay in the soil. It is necessary to examine possibility of leaf (foliar) application of N
fertilizers, as well as other timings of nitrogen fertilizers application.
Literature
Agenbach, W. A. A. (1977). A study of must nitrogen content in relation to incomplete
fermentations, yeast production and fermentation activity. In Proceedings of South African
Society for Enology and Viticulture, Cape Town
Amerine, M. A., Ough C. S. (1980). Methods for analysis of musts and wines. John Wiley
and Sons, New York, 794p
Bavaresco, L., Pezzutto S., Ragga A., Ferrari F., Trevisan M. (2001). Effect of nitrogen
supply on trans-resveratrol concentration in berries of Vitis vinifera L. cv. Cabernet
Sauvignon. Research note. Vitis. 40 (4): 229-230
Bell, A. A., Ough C. S., Kliewer W. M. (1979). Effects on must and wine composition, rates
of fermentation and wine quality of nitrogen fertilization Vitis vinifera var. Thompson
Seedless grapevines. Americain Journal of Enology and Viticulture. 30 (2):124-129
Bell, S.-J., Henschke, P. A. (2005). Implications of nitrogen nutrition for grapes, fermentation
and wine. Australian Journal of Grape and Wine Research. 11(3): 242-295
Bisson, L. F. (1991). Influence of nitrogen on Yeasts and fermentations of grapes.
International Symposium on Nitrogen in Grapes and Wine, J. M. Rantz (Ed.). pp 78-89. Am.
Soc. Enol. Vitic., Davis, CA
Butzke C. E., Dukes B. C. (1998): NOPA Procedure, Concentration of Primary Amino Acids
in Grape Juice, UC Davis Cooperative Extension
Christensen, L. P., Bianchi M. L., Peacock W. L., Hirschfelt D. J. (1994). Effect of nitrogen
fertilizer timing and rate on inorganic nitrogen status, fruit composition, and yield of
grapevines. Americain Journal of Enology and Viticulture. 45 (4): 377-387
Huang, Z., Ough C. S. (1989). Effect of vineyard locations, varieties, and rootstocks on the
juice amino acid composition of several cultivars. American Journal of Enology and
Viticulture. 40(2): 135-139
Ingledew, W. M., Kunkee R. E. (1985). Factros influencing sluggish fermentations of grape
juice. American Journal of Enology and Viticulture. 36: 65-76
O.I.V. „International Code of Oenological Practices”, edition 2001, Paris
Peacock, W. L., Christensen L. P., Hirschfelt D. J. (1991). Influence of timing of nitrogen
fertilizer application on grapevines in the San Joaquin Valley. American Journal of Enology
and Viticulture. 42(4): 322-326
Spayd, S. E., Wample R. L., Evans R. G., Stevens R. G., Seymour B. J., Nagel C. W. (1994).
Nitrogen fertilization of White Riesling grapes in Washington. Must and wine composition.
American Journal of Enology and Viticulture. 45(1): 34-42
Utjecaj dušične gnojidbe na brzinu i tijek fermentacije mošta Rizlinga
rajnskog (Vitis vinifera L.)
Sažetak
Dušično gnojivo (urea) aplicirano je ručno u vinograd Rizlinga rajnskog u količinama od 0,
23, 70 ili 117 kg N/ha u periodu od 2006 do 2009 godine. Brzina fermentacija je rasla sa
intenziviranjem dušične gnojidbe, iako su samo jedan mošt od 0 kg N/ha, odnosno dva mošta
od 23 kg N/ha uspješno odfermentirala. Svi moštevi od 70 i 117 kg N/ha uspješno su
odfermentirali, ali je fermentacija trjala neprihvatljivo dugo. Produženo trajanje fermentacije
u uskoj je vezi sa niskom razinom slobodnog amino dušika u moštu, koji je varirao od 13 do
40 mg/L. Dušična gnojidba utjecala je i na višu razinu ukupne kiselosti u moštu.
Ključne riječi: brzina fermentacije, dušik, gnojidba, mošt