Winegrape
growers and winemakers have long sought a method for selecting the optimum time
to harvest winegrapes. Measurements of
sugars (Brix, or soluble solids), pH, acidity, anthocyanins, berry weight,
glutathione, arginine, protein levels, and terpenes, among others, were made,
but they did not correlate very well with optimum wine quality. Some researchers looked for combinations of
factors, and found that ºBrix x pH, ºBrix
x pH2, and especially ºBrix/acidity
were much more useful in making harvest decisions than the individual factors
alone.1-6 These factors continue to be recommended by major
reference books.7-11 When using the ºBrix/acidity ratio, values in
the range of 30 – 32 have proven optimal, although best time to harvest varies
slightly between varieties and between general climate.
Some
additional techniques have been developed, such as gas chromatographic analysis
of aroma components, spectrophotometric measurement of anthocyanin levels, and
near infrared analysis of specific phenols.
For now, however, these techniques are at best research oriented, off
line methods.
There is
one method that has recently gained favor among some winemakers as a means of
judging time to harvest: sensory
analysis of grapes, otherwise known as tasting. A September 5, 2006, Wine Industry Symposium
on this technique was recently described in “Wine Business Monthly.”12
There are two schools of thought on this technique. First, at an earlier conference discussing
the technique of using taste to judge optimum time to harvest, Dr, Richard
Smart stated "Winemakers go into the vineyards and
they chew on some grapes, and they look at the seeds and the stems, and they
mumble a few things, and then they proclaim the harvest date. And curiously,
that date is always in the future, never in the past. I never heard a winemaker
taste the grapes and say, 'Darn, we got here too late’."13 Also,
in a recent study expert wine tasters showed considerable variation in their
assessments of wine quality.14
What do I
suggest? Perhaps we should follow the
advice of the late renowned French enology researcher Emile Peynaud:15 “Attempts have been made to express the state
of maturity of the grape using certain ratios between different ingredients. The sugar/acidity ratio is the simplest and
most meaningful. Since sugar levels rise
while acidity diminishes during ripening, the sugar/acidity ratio rises sharply
and develops more quickly than its two factors.
Although the accumulation of sugars and the combustion of acids not
being subject to the same factors, take place independently in the grape, this
index is a fairly accurate expression of the state of ripeness. Its value depends on the variety.” And if there has been a change in weather
conditions such as the very cool spring this year in Oregon, perhaps doing a
little extra canopy manipulation (e.g., leaf removal) will produce much better
grapes than simply letting them hang for an extended period of time.
What do you
think?
1. C.
S. Ough, V. L. Singleton, “Wine quality prediction from juice Brix/acid ratio,”
Am. J. Enol. Vitic., 19 (3): 129 -
138 1968.
2. C.
S. Ough, C. J. Alley, “Effect of Thompson seedless grape maturity on wine
composition and quality,” Am. J. Enol.
Vitic., 21 (2): 78 - 84 1970.
3. J.
Ribereau-Gayon, E. Peynaud, P. Ribereau-Gayon, P. Sudraud, Traite d’oenologie sciences et techniques du vin, vol. 2, Dunod,
Paris, 1975.
4. B.
G. Coombe, R. J. Dundon, A. S. Short, “Indices of sugar-acidity as ripeness
criteria for winegrapes,” J. Sci. Food
Agr., 31: 495 - 502 1980.
5. C.
S. DuPlessis, P. C. Van Rooyen, “Grape maturity and wine quality,” S. Afr. J. Enol. Vitic., 3 (2): 41 -45 1982.
6. P.
C. Van Rooyen, P. C. Ellis, C. S. Du Plessis, “Interactions between grape
maturity indices and quality for Pinotage and Cabernet sauvignon wines from
four localities,” S. Afr. J. Enol.
Vitic., 5 (1): 29 - 34 1984.
7. B.
W. Zoecklein, K. C. Fugelsang, B. H. Gump, F. S. Nury, “Wine Analysis and
Production,” Chapman and Hall, 1995.
8. R.
B. Boulton, V. L. Singleton, L. F. Bisson, R. E. Kunkee, “Principles and Practices of Winemaking,” Chapman and Hall, 1996.
9. P.
Iland, A. Ewart, J. Sitters, A. Markides, N. Bruer, “Techniques for Chemical Analysis and Quality Monitoring During
Winemaking,” Patrick Iland Wine Promotions, 2000.
10. J.
L. Jacobson, “Introduction to Wine
Laboratory Practices and Procedures,” Springer 2006.
11. P.
Ribereau-Gayon, D. Dubourdieu, B. Donneche, A. Lonvaud, “Handbook of Enology,” Vol. 1, 2006
12. M.
Greenspan, “Assessing Ripeness through Sensory Evaluation,” Wine Business
Monthly, Nov. 2006.
13. D.
Berger, “”Water into Wine: the smoking gun,” Wines & Vines. 86 (3):
52 – 56 2005.
14. R.
Gawel, P. W. Godden, “Evaluation of the consistency of wine quality assessments
from expert wine tasters,” Aust. J. Grape
& Wine Res., 14: 1 - 8 2008.
15. E.
Peynaud, “Knowing and Making Wine,”
Wiley-Interscience, 1982.
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