VI Grape Quality

Aroma is the key determinant of wine quality. The majority of aroma-producing chemicals in wine grapes are non-volatile glycosides. Vancouver Island is a cool climate wine growing region known for high quality aromatic wines, particularly those made from the Pinot Gris varietal, the most popular white varietal grown on Vancouver Island and in British Columbia. Common vineyard practices like grape vine leaf removal have been shown to accelerate ripening and positively effect glycoside aroma composition but also increase berry susceptibility to sun burn. A potential solution is the application of kaolin, an organic engineered clay, which acts as a “sunscreen” for the fruit. This research proposes to identify the combination(s) of leaf removal treatments and kaolin application on Pinot Gris grapes that promote optimal grape aroma production as revealed by gas chromatography and mass spectrometry. This work is supported by WIGA and Investment Agriculture Foundation of BC

The production of grapes and wine is a relatively new industry in British Columbia (BC) but has grown rapidly over the past 30 years. Currently the wine industry contributes Can$2.8 billion and 12,000 jobs to the provincial economy. Most grape production occurs in the dry, hot climates of the interior, where most of the industry infrastructure and research is focused. A smaller but rapidly emerging wine region is Vancouver / Gulf Islands, located within the maritime climate on the west coast.  Commercial scale wine production on Vancouver Island and the surrounding Gulf Islands began in the early 1980’s with the government funded “Duncan Project” which introduced numerous varietals to the region to determine which were best suited to the Island climate and the soils. Since then, the region has become known for aromatic white wines, particularly those made from Pinot Gris. The grape growers on Vancouver Island are represented by the not for profit industry organization Wine Islands Growers Association (WIGA), whose priority is the establishment of industry-relevant research capacity in the region for the benefit of its members.

Pinot Gris is a Vitis vinifera mutant of Pinot Noir first described in the middle ages. It originated in Burgundy, France, but is now found throughout the wine-producing world. It is characterized by small compact clusters with skin colours ranging from blue-grey, orange to brown. Pinot Gris wine styles vary greatly, from the rich, full-bodied wines of the Alsace region, to the crisp light Pinot Grigio made in Italy. In British Columbia, Pinot Gris is the most planted white grape varietal making up 20% of all grape production. Despite being a staple in the region, little research has been undertaken to determine optimal Pinot Gris growing regime.

The limited amount of arable land in coastal BC incentivizes BC wine producers to pursue quality over quantity to maximize value from the limited space. What constitutes wine quality is complex though flavour profile is a dominant determinant, and aroma is the key component of flavour. Wine aroma develops and complexifies during fermentation and aging and is derived from the aromatic compounds present in the grapes at harvest. To improve the aroma quality of grapes, vine canopy management techniques are often employed to modify the micro climate of the grapes creating a positive growing environment. 

The effects of canopy management techniques on grape aromas are difficult to assess. Grape aroma compounds are found in two states: free (volatile) and bound (glycoside) aroma compounds. In the bound glycoside state an aromatic compound is bound to a sugar molecule making it non-volatile and thus undetectable by human senses (tasting a grape at harvest gives little indication of the future wine). Fermentation digests bound sugars and converts glycosides to volatile (now detectable) compounds.  Since most grape aroma compounds are found in the glycoside state, quality assessment prior to fermentation and aging is not typically possible. Gas chromatography and mass spectrometry (GC/MS) are used to identify and quantify compounds such as non-volatile glycosides in complex mixtures such as grape juice. GC/MS allows us to measure the effects of vineyard treatments directly on grapes before processing and avoiding uncontrolled sources of variance introduced during processing, fermentation and ageing.

Manipulations will be performed on three vineyards in the Cowichan Valley of Vancouver Island all growing Pinot Gris. Vineyards have been selected for their proximity to each other and their similar north to south row orientation. A randomized block design is used where each experimental unit will be a group of 6 vines in the same row. The units will be selected for their even growth. One of four treatments will be randomly applied to these units.
Experimental treatments:

  • One of two severities of leaf removal on all treatment units: To be applied when berries reach pea size
    • Industry standard: only on the east side of the canopy
    • Severe: all leaves removed from the apical cluster down
  • Experimental units will receive one of two kaolin treatments: To be applied at veraison (and following rain events)
    • Kaolin
    • No kaolin
  • Total of five repetitions for each treatment

(Standard LR-No Kaolin | Standard LR- Yes Kaolin | Severe LR-No Kaolin | Severe LR- Yes Kaolin)

  • 20 experimental units per vineyard * 3 vineyards
  • 60 experimental units total

Response variables include:
Vine Physiology – phenology (bud burst, flowering, fruit set, veraison, and harvest dates)
                              – leaf area
                              – canopy density (using Viticanopy)
                              – vine size (using pruning weights)
                              – yield per vine (Ravez Index)
Berry Temperature is monitored in two ways
        i) hydrochron iButton (d1923-F5) data loggers placed in the fruit zone to record air temperature  and relative humidity every 30
           minutes through the growing season from bloom to harvest
        ii) berry temperature reducing effectiveness of kaolin will be assessed using an infrared thermometer to directly measure berry   
             temperature on treated and untreated units
Gas Chromatography/ Mass Spectrometry To identify and quantify the aroma compounds present in Pinot Gris under four leaf removal  and Kaolin treatments, we are using a Varian 3800 Gas chromatograph attached to a Varian 2200 mass spectrometer. Using twelve aroma compound standards known to be important to Pinot Gris aroma components to create a calibration curve and subsequently analyze both volatile and glycoside aroma compounds using solid phase microextraction (SPE).