An analysis of Finger Lakes Grapes—Sugar and TA Levels

based on Fall Bright’s vineyard data 2001-2009

By Dale Ims

Fall Bright’s website, www.fallbright.com, in addition to listing sugar and TA (titratable acidity) properties for the 25 or so varieties produced on their Keuka Lake vineyard during the most-recent crop year, has similar data for a number of previous years. I keyed the juice-property values into an Excel spreadsheet for 14 varieties of grapes in which I had some interest and/or for which there was data available for the years 2001 to 2009 (the vagaries of weather and/or plant diseases resulted in crop failures for some varieties in some years, so the data tables were incomplete for those varieties).

So what can we learn from the data?

Analysis by grape variety

One thing that I did was to attempt to get some sense of the varietal variations in sugar content and titratable acidity. To do that, I averaged the TA and sugar content values, respectively, for each variety over the 9-year period for which there is data and then combined those calculated averages into a single bar chart (see Figure 1).

Figure 1: Average Sugar Content and TA by Grape Variety. Mean sugar content (%) is in blue; TA (g/l) is in red

It is most enlightening to look at Figure 1 in light of the necessary sugar content, or degrees Brix, to get a wine with 12% alcohol (about 22%), and in light of the desired TA in a finished wine (6 to 7 g/l).  In fact, the chart shows us that, on average, we needed to adjust all the juices—adding sugar in order to get 12% alcohol in the finished wines and doing something to reduce the acid contents to acceptable levels.

The standout varieties in the above chart were Vignoles and Niagara for sugar content, with the former having the highest mean sugar content (near 21%), and the latter having the lowest (about 12.5%).  Similarly, for TA the max/min varieties were Baco with about 14.5g/l and Niagara with about 7.6g/l.

Of course, there were year-to-year variations in the sugar contents and TA values for each of the varieties of juices, and in some years with some varieties there may have been no need to add sugar and/or reduce the acid level.

Analysis by vintage year

In addition to the above analysis, where we pooled all the data values for a given variety to produce what might be termed variety-averages, we can look at season-to-season variations by pooling all the data values for a given year to produce what might be called season-averages. The resulting season-averages for sugar content and TA are shown in Figure 2.

Figure 2: Average Sugar Content and TA by Vintage (All Varieties). Mean sugar content (%) is in blue; TA (g/l) is in red

Note in Figure 2 that years in which the sugar contents were high also had low TA values, and that the converse was also true.  This chart shows that last year (2009) was an especially bad year, with low sugar contents and high TAs. In fact, using the sugar content and TA values as indicators, one might say that ’09 was the worst year of the decade—although only slightly worse than ’03.

I do not know to what extent the results from Fall Bright are representative of those from other Finger Lakes vineyards, but in those cases where I have been able to compare the properties of juices from other local suppliers to those values reported by Fall Bright, I have found the levels and year-to-year trends to be similar.

If the past nine years are any indication, those of us who make grape wine from locally-grown grapes and juices need to know how to deal with high-acid, low-sugar fruit and juices that result from our local growing conditions—especially if we want to use some of the more difficult varieties!