In this study, type, temperature, and time elapsed from initial opening were examined to determine their influence on pH of white wine. A 23 experimental design was used and four bottles each of Chardonnay and Pinot Grigio were used as replicates. Of the three individual factors and four possible interactions, there were three significant results (p<.05) for which the null hypothesis was rejected. Practical applications of these results suggests that individuals can benefit by making an effort to hold wine glasses by the stem, preventing heat transfer and subsequent increases in acidity.

1. Lindsay Meyer
BIOS 42411-04
2 May 2007
The Science of What’s in the Bottle: Factors Which Influence pH of White Wine
ABSTRACT
In this study, type, temperature, and time elapsed from initial opening were examined to
determine their influence on pH of white wine. A 23
experimental design was used and four
bottles each of Chardonnay and Pinot Grigio were used as replicates. Of the three individual
factors and four possible interactions, there were three significant results (p<.05) for which the
null hypothesis was rejected. Practical applications of these results suggests that individuals can
benefit by making an effort to hold wine glasses by the stem, preventing heat transfer and
subsequent increases in acidity.
INTRODUCTION
In February 2005, it was reported that by 2008, Americans would account for 25% - a full
quarter of all wine drunk in the world (Anderson 2005). As the US prepared to outdo even its
oenophile-friends in France, Italy, and Spain, it is appropriate to become more educated
consumers of this drink. Popular culture purports that the best white wines have a pH between
3.3 and 3.7 (Pandell 1999). However, a variety of factors – including type, temperature, and
time elapsed from initial opening, may affect the overall quality of wine. In designing this study,
it was expected that all factors – ages, temperatures, and types would produce equal pH readings,
and that there would be no two or three-way interactions between factors (null hypothesis).
METHODS
Four different bottles each of Chardonnay and Pinot Grigio (“types”) were obtained and
randomly assigned numbers from one through four. Beginning with Bottle 1 of Chardonnay,
eight mL aliquots were added to three clean test tubes. This process was repeated for Pinot
Grigio. Using a pH-meter, the pH of each sample was obtained at 20°C and 40°C for both types
of wine with treatments being selected at random with a random numbers table. This process
was repeated for all remaining bottles (2, 3, and 4) for both types. This procedure was repeated
again after 7 days. An analysis of variance (ANOVA) statistical test was performed in SYSTAT
to analyze the data. Residuals were saved to make Normal Probability and Residual Plots. A
KS/Lillefors test was performed to analyze the distribution.
RESULTS
Data collected between t = 0 and t = 7 did not appear to differ. However, the pH values
for pinot grigio were lower, and more acidic than those of chardonnay. Increases in temperatures
seemed to have an inhibiting effect on pH values.
Figure 1-1: Raw pH data as collected at two times, for two types of
wine, at two temperatures. Bottles represent replicates, k=4.
Type
Temp 20°C 40°C 20°C 40°C
1 3.159 3.064 3.097 2.810
2 3.340 3.111 3.110 2.853
3 3.259 3.141 2.985 2.865
4 3.343 3.118 3.111 2.874
Chardonnay Pinot Grigio
ttleBo
Type
Temp 20°C 40°C 20°C 40°C
1 3.309 3.186 3.052 2.885
2 3.200 3.161 3.042 2.936
3 3.291 3.206 3.051 2.870
4 3.291 3.215 3.051 2.892
Chardonnay Pinot Grigio
Bottle
T = 0 days T = 7 days
Page 1 of 4

2. Lindsay Meyer
BIOS 42411-04
2 May 2007
Statistical testing with SYSTAT produced an ANOVA table (Figure 1-2) with three p-
values which were greater than α = 0.05: type, temperature, and time*temperature. Their
respective null hypotheses of equal pH (for single factors) or independence (for interaction
terms) were rejected. The remaining four p-values were less than α = 0.05 and their respective
null hypotheses of equal pH (for single factors) or independence (for interaction terms) were
accepted.
Figure 1-2: Analysis of Variance Table displays the test-statistics for all
three factors plus the three 2-way interactions and one 3-way interaction.
Source SS df MS F P Conclusion
TYPE$ 0.478 1 0.478 226.249 0 Reject
ELAPSEDTIME$ 0.005 1 0.005 2.344 0.139 Accept
TEMPERATURE 0.196 1 0.196 92.79 0 Reject
TYPE$*ELAPSEDTIME$ 0.002 1 0.002 0.925 0.346 Accept
TYPE$*TEMPERATURE 0.009 1 0.009 4.063 0.055 Accept
ELAPSEDTIME$*TEMPERATURE 0.012 1 0.012 5.911 0.023 Reject
TYPE$*ELAPSEDTIME$*TEMPERATURE 0 1 0 0.046 0.831 Accept
Error 0.051 24 0.002
Further analysis was performed in SYSTAT. The residual plot demonstrated equal
variance among treatments as most of the points occurred along the line representing the
expected normal distribution. The normal probability plot was indicative of normality, with the
residuals occurring along a horizontal band.
2.8 2.9 3.0 3.1 3.2 3.3
ESTIMATE
-0.2
-0.1
0.0
0.1
RESIDUAL
Figure 1-4: Normal Probability
Plot shows the residuals occurring
within a reasonably horizontal band,
demonstrating normality.
Figure 1-3: Residual Plot shows the
residuals versus expected values and
displays equal variance among
treatments.
-0.2 -0.1 0.0 0.1
RESIDUAL
0.01
0.99
ExpectedFractionofDataforNormalDistribution
Page 2 of 4

3. Lindsay Meyer
BIOS 42411-04
2 May 2007
Finally, the data were tested with the KS-Lillefors test for normality. The p-value of
0.065 exceeded alpha = 0.05 and indicated that the data were normal.
Figure 1-5: Kolmogorov-Smirnov one sample test is a criterion
for accepting or rejecting the null hypothesis of normality.
Because p>α, the data are normally distributed.
VARIABLE N-of-Cases MaxDif Lillefors Probability (2-tail)
RESIDUAL 32 0.15 0.065
DISCUSSION
According to the p-values produced in the ANOVA table, we reject the null hypothesis
that both types of wine produce equal pH. This indicates that chardonnay and pinot grigio do not
have equal pH’s. The same was true for the two temperatures, 20°C and 40°C – that they do not
give rise to equal pH values. The null hypothesis for equal pH values at two different times – 0
and 7 days was accepted, with p = 0.139. Empirical differences in formulation are the likely
cause of pH differences between types. From differences in fermentation technique to
differences in grape harvests, it is not surprising that the two brands had significantly different
pH levels. The significant difference in pH at 20°C and 40°C is more difficult to source. It is
possible that pH-altering chemical reactions occur as heat is added.
For the three 2-factor interactions, only time crossed with temperature was rejected,
signaling an interaction between factors. The null hypothesis of the one 3-way interaction was
accepted; differences in pH are independent of type, temperature, and elapsed time.
The practical application of this study is that pH of wine changes significantly as
temperature is manipulated. Increases in temperature lead to decreases in pH, thus increasing the
overall acidity. There are also differences in pH between chardonnay and pinot grigio, which
suggests that there are differences in the pH between all types of white wine. Additional
differences may exist for different brands of the same type of wine. Disparities may be the result
of differences in production, harvest techniques, and general composition. Further
experimentation could be performed with additional types (white zinfandel, sauvignon blanc, and
so on).
Oenophiles can rest easier, equipped with the knowledge that it’s acceptable to drink
from an opened bottle of wine, even after leaving it out for a week – pH doesn’t significantly
change during this time horizon. While the prevailing notion is that one should keep white wines
stored in a refrigerator (5°C), consumers should be aware that this will decrease the acidity.
Sophisticated wine drinkers can also be commended for insisting that wine glasses ought to be
held by the stem. Human heat transfer from hand to glass to wine could expedite the warming
process, thereby increasing acidity.
This study did not attempt to make any conclusions about taste. Individual preferences
are ultimately responsible for such determinations and were not evaluated in tangent with this
study. Additional experiments could be performed to allow multiple human subjects to sample
each replicate and provide numerical feedback regarding their level of satisfaction with respect
to taste. This would be a proxy for taste and pH. Other interesting follow up experiments could
contrast the pH of reds versus whites or a wider range of temperatures.
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4. Lindsay Meyer
BIOS 42411-04
2 May 2007
Page 4 of 4
m the same
ottle. Additional statistical analysis using a block effect for the four bottles of each type would
ts and represent a viable opportunity for additional study.
nderson, Gordon. “World’s Biggest Wine Country: USA.” CNN Money 2005. Accessed 1
andell, Alexander J. “The Acidity of Wine.” The Wine Perspective 1999. Accessed 1 May
2007 <http://www.wineperspective.com/the_acidity_of_wine.htm>
In addition, this study had flawed experimental design because of pseudo replication.
Rather than using 32 different bottles of wine – or 16 of both types, aliquots were fro
b
help to remove these effec
LITERATURE CITED
A
May 2007 <http://money.cnn.com/2005/02/18/pf/goodlife/america_wine/>
P