Frontenac gris, the white wine version of Frontenac, started as a single bud mutation yielding gray (thus named gris) fruit and amber-colored juice. The vine exhibits the same optimum growth characteristics as Frontenac, and requires the same cultural practices. Arching canes and minimal tendrils provide easy training and pruning to simplify vine management. In Minnesota, Frontenac and Frontenac gris ripen in late mid-season, and are good sugar producers with 24-25° Brix not uncommon.
Frontenac gris wines present aromas of peach and apricot with hints of enticing citrus and tropical fruit. A brilliant balance of fruit and acidity creates lively, refreshing wines. Unique and complex flavors make this an excellent grape for table, dessert, and ice wines.
Frontenac gris Viticulture
Frontenac gris is a grape cultivar with bronze-gray ("gris" in French) colored fruit suitable for white wine production. Frontenac gris was originally identified as a sport of Frontenac, a cultivar with black fruit that was introduced from the University of Minnesota grape breeding program in 1996. Like Frontenac, Frontenac gris has excellent cold hardiness and disease resistance, together with very good productivity and wine quality.
Frontenac gris originated as a single cane sport on a plant of Frontenac growing at the University of Minnesota Horticultural Research Center. The single cane was first observed with fruit in 1992. Subsequently plants were propagated from this cane and have all produced gray rather than black fruit. Frontenac was derived from a cross between the French hybrid cultivar Landot 4511 and the University of Minnesota Vitis riparia selection #89, found growing wild near Jordan, Minnesota.
Frontenac gris vines are identical to those of Frontenac. They are "grower-friendly" due to their winter hardiness, disease resistance, strong vigor, desirable growth habit, and high yield potential. Frontenac gris has proven sufficiently cold hardy for consistent production in central Minnesota where temperatures frequently reach -30°F when good viticultural practices are used . Outdoor and laboratory freezing tests have shown it to be more cold hardy than Marechal Foch and Seyval Blanc.
The clusters of Frontenac gris are loose and medium in size, averaging 131 g/cluster and 18 cm (7 in) in length, and conical in shape with a small shoulder. Berries are small to medium averaging 1.1 g/ berry and 12 mm (0.5 in) in diameter. Sugar levels have been high, averaging 25.6° brix but reaching levels as high as 28° brix. Acid levels have also been higher than most cultivars at 13.7 g/l. Due to these high levels of both sugar and acidity, Frontenac gris wines often require leaving residual sugar in order to produce a well balanced wine in northern climates.
Frontenac gris juice frequently exhibits a slight pink or peach coloration derived from the lightly pigmented skin of the fruit. The juice can be fermented to produce either white table wine or dessert wine. The wine tends to have good body and pleasant aromas, with very little of the herbaceous qualities associated with V. riparia and many interspecific grape hybrids. The most common aroma component identified by tasters has been peach, but apricot, citrus, and tropical fruit aromas have also been noted. "Foxy" aromas characteristic of V. labrusca have not been detected.
Frontenac gris should be a useful variety in other cold climate viticulture areas (USDA plant hardiness zones 4 and 5) of the eastern US and Canada where Frontenac has already become established.
Frontenac gris Enology
Frontenac gris has shown the potential to be produced in a variety of styles. Its bronze skin lends color to the juice, resulting in a wines typically ranging from pale gold to rich amber. Wines are typically intensely fruity, exhibiting dominant peach and tropical fruit flavors, especially pineapple, and hints of honey. The fruity palate and high acidity make Frontenac gris an excellent candidate for semi-sweet to dessert wines. Frontenac gris has also shown well as a dry to off-dry table wine.
Average harvest chemistry from the HRC vineyard (2003-2005):
TA: 14 g/L
Fermentation temperature and yeast. To retain fruity esters, Frontenac gris is best fermented at cool temperatures (55°F) with aromatic yeasts. Due to the high sugar, yeasts that can tolerate high alcohol levels are necessary to ferment Frontenac gris to dryness. Acid-reducing yeasts have also been utilized succesfully greatly diminishing aromatic intensity.
Sweet and Dessert wine production
Frontenac gris benefits from residual sugar, which balances the high acid and intensifies the rich fruit character. The key to successful palate balance in sweet wines is the retention or addition of appropriate sweetening. This can be accomplished three ways: by stopping fermentation, by back-adding sugar, or by reserving juice at harvest and blending it in following fermentation.
Stopping Fermentation: One means of achieving an appropriate acid:sugar ratio is by stopping fermentation, either by filtration or cold-stabilization. Membrane filtration (not plate-and frame) at 0.45 or smaller should stop fermentation instantly. Stopping fermentation via cold-stabilization is tricky, as it can take hours to days for the yeast to cease activity. This delay is largely dependent upon the equipment and conditions available. Of these methods, filtration is much easier for commercial wineries, as the lag between action and cessation of fermentaion is greatly diminished. Less aggressive, aromatic yeasts are desirable, as these strains tend to slow down as alcohol levels increase. Preserving some of the natural sugar in the wine can increase aromatic intensity and mouthfeel. This technique has the added benefit of keeping alcohol levels moderate.
Back-adding sugar or juice: The simplest way of sweetening Frontenac gris is to ferment the wine to complete dryness, then back-add sugar. This technique has the advantage of allowing the winemaker to perform bench trials of various sweetness levels prior to adjusting the wine, so the final product can be fine-tuned to a desired level of sweetness.
Another back-sweetening method involves reserving a portion of juice at press time, fermenting the rest of the juice to dryness, then back-blending the reserved juice to provide sweetness and intense fruit character. Care must be taken in storing the reserved juice; usually this portion (called sussreserve) is clarified, treated with SO2 and frozen until needed.
In either case, it's important to make sure that yeast have been removed, via sterile filtration, or inactivated with potassium sorbate. Sterile filtration is much preferred, as the necessary inhibitory rate of sorbate additions can vary, and may produce a chemical off-note in wines if overused.
"Faux" Ice Wine
Trials with faux ice wine have shown tremendous potential. This extremely sweet dessert wine can produced two ways: by freezing grapes after harvest and pressing them frozen (which requires a specialized press) or freezing juice after pressing and allowing slow thawing to control °Brix. Traditional ice wine (letting fruit freeze on the vine) decreases overall vine hardiness and can result in significant injury in harsh winters.
Off-dry table wine
Frontenac gris table wines are best finished with some residual sugar, to boost the perception of fruit and balance acidity. As with dessert wines, residual sugar can be achieved by stopping fermentation or back sweetening. Attempts to reduce acidity with malolactic fermentation (MLF) have not been successful, as the diminished fruit tends to leave the wine too acidic. Frontenac gris table wines are usually ameliorated to reduce alcohol and acidity, and often treated with potassium bicarbonate or other chemical deacidification method to bring the wine into balance.