Size Doesn’t Matter: Putting a Traditional Grape Growing Theory to the Test

Historically, there are many winemaking practices that may or may not exactly be backed-up scientifically. Today’s article examines one of those practices/theories: that small grapes produce better red wines. The thought process behind this idea is that smaller grapes may have a higher skin-to-flesh ratio, and thus more of the compounds commonly found in grape skins may be extracted and thus lead to higher quality wines.  According to the authors of a study published early this year, this theory doesn’t take into consideration variations in skin thicknesses or seed composition/size.

The study presented today, published in the January 2020 issue of the Journal of Science of Food and Agriculture, aimed to take a scientific look at this tradition of selecting for smaller berries under the assumption that those berries would produce higher quality wines.

For the full citation of this article, see below.  Alternatively, there was an online summary of this article by one of the researchers at the Science & Wine (Ciencia & Vinho) website, which I encourage you to read for more technical details regarding the project and the results (instead of the brief summary I will provide here).  That article may be found here.

“wine grapes” by def110 is licensed under CC BY-NC-SA 2.0

Brief Methods

Grapes used in this study were own-rooted Vitis vinifera Carménère from William Fevre vineyards in Maipo Valley, Chile from the 2015 vintage.

Grapes were sampled/harvested from two different plots (named 94N and 99S) that underwent the same viticulture practices that were managed by the same grower. 

Grapes were manually harvested from 30 vines in 3 consecutive rows, which were then split up: some for berry analysis, while the rest underwent alcoholic fermentation, 15 days of maceration, stabilized, bottled, then stored for 3 months before further analysis was performed.

The following characteristics were measured/analyzed:

  • Grape skin thickness
  • Soluble polysaccharides
  • Phenolic index of wine
  • Total anthocyanins
  • Proanthocyanidins
  • Flavanols
  • Volatile compounds

Selected Results

  • The two vineyard plots experienced similar weather and physiological conditions during the growing season.
  • Grapes on vines from both sites showed similar vigor, yield, and ripening.
  • Grape berry size was different between sites at harvest.
  • Grapes from both sites showed the same technological and phenolic maturity.
  • Grapes were smaller at site 94N than the site 99S.
  • Average number of seeds per grape were very similar between sites.
    • Site 94N had more grapes containing two seeds than grapes at the 99S site.
  • Mass and volume of seeds were statistically similar between site 94N and 99S
    • This indicates seed size does not dictate berry size, since mass and volume of seeds were more or less the same yet the berry size was different between sites.
  • The proportion of seeds was 2x higher in 94N grapes compared to 99S grapes (despite the grapes being smaller in size).
  • Grape skins were thicker in berries at the 99S site compared to the 94N grapes.
  • Relative proportion of skins and skin-to-flesh ratios were greater for grapes at the 99S site compared to the 94N grapes.
  • Despite showing differences in phenolic evolution during the fermentation process, after maceration the wines from both contained statistically similar concentrations of total phenols.
  • After stabilization, the wines from 99S grapes had statistically higher total phenols than wine from the 94N grapes.
  • Anthocyanins were statistically higher in 99S wines from day 4 of maceration until the end, compared to 94N wines.
  • Aldehyde content was statistically similar between wines from the two sites.
  • Volatile alcohol levels were higher in wines made from 99S grapes compared to the 94N site.
  • 2-phenylethanol (produced by the yeast and known for a rose-like aroma) was about 25% greater in concentration in the wines made from 94N grapes compared with wines from the 99S grapes.
    • 99S wines had more alcohols from grapes and less alcohol produced by yeasts compared to 94N wines.
  • Total esters were statistically similar between wines made from grapes at both sites.
  • Acetate esters were higher in 99S wines than 94N wines (mostly isoamyl acetate).
  • Linalool and α-terpineol (terpenes) were statistically higher in 99S wines compared to 94N wines.
  • 99S wines had a darker color than 94N wines.
  • Monomeric flavanol levels were higher in 94N wines than 99S wines.
  • Dimeric flavanol levels were statistically similar between the wines from the two sites.
  • Higher mean degree of polymerization levels for polymeric flavanols were found in 94N wines compared with 99S wines.
  • Total extracted polysaccharides were statistically similar between grape skins at both sites.
  • 99S wines had statistically higher amounts of soluble polysaccharides compared with 94N wines.

Conclusions

In summary, total aldehydes, alcohols, esters, and norisoprenoids were statistically similar between finished wines at both vineyard sites. On the other hand, total acids, total terpenes, and acetate esters were statistically higher in 99S wines (bigger grapes, thicker skin) compared to 94N wines (smaller grapes).

Results also showed that greater anthocyanin extraction may be related to the proportion of skin (skin-to-flesh ratio) rather than the size of the berries themselves (surface-to-volume ratio).  Similarly, skin color appeared to be related to skin thickness rather than the size of the berry itself.

“wine grapes” by def110 is licensed under CC BY-NC-SA 2.0

According to the authors of this study, grape berry size should not be used as a quality parameter for grapes if they are coming from different vineyard sites. In other words, just because grapes are smaller doesn’t mean that they are going to produce higher quality wines.  As the results of this study show, many of the differences in chemical analyses were due to factors governed by skin thickness, which in this case happened to belong to the larger 99S grapes.

Can you have smaller grapes that produce higher quality wines? Of course you can, if those wines you are comparing them to have a smaller skin-to-flesh ratio.  Skin thickness appears to play an important role in finished wine quality, and not necessarily the size of the grape itself.

For further reading….

Source:

Cortiella, M.G., Úbeda, C., del Barrio-Galán, R., and Peña-Neira, A. 2020. Impact of berry size at harvest on red wine composition: a winemaker’s approach. Journal of the Science of Food and Agriculture 100(2): 836-845.

Detailed post related to this and another paper:  Does Berry Size Matter? (last accessed 08/19/2020)