Bisson Glera Explained

Posted on Posted in Rosenthal Wine Merchant News

If it seems unusual that Pierluigi Lugano, the proprietor and vignaiolo behind Bisson in Liguria, is also our source for the declassified Prosecco known as Glera, one might ask how this wine came to be.  After all, Prosecco hails from an appellation 400 kilometers to the northeast of Lugano’s hometown of Chiavari in Liguria, in an area of the Veneto abutting the foothills of the Dolomites.

Lugano’s tie to the area is his longtime friend Eli Spagnol, who is the proprietor of Torre Zecchei in Valdobbiadene.  This location is important to note, as it is the namesake of the Conegliano Valdobbiadene Prosecco Superiore DOCG, arguably the finest site for Prosecco in the region.  All of the wines in this appellation are sourced exclusively from the Glera grape, which is how we came to the name “Glera” for our bottling.  The sole reason the Glera is not classified under the DOCG is the closure: the wine is under a crown cap, which falls outside of recently changed appellation laws that require a cork closure.  We have experimented with returning to a cork for this wine, but ultimately made the decision to stay with the crown after careful consideration of feedback from the market.

bisson-glera-vineyardWhile most of the more commercial wine labeled as Prosecco is sourced from flat, machine-worked vineyard land in the plains below the foothills, the wine sourced from the Valdobbiadene appellation is from steeply-sloped hillsides in the series of valleys ranging east from the village.  The soil is composed of glacial deposits from the Dolomites.  Due to the landscape, all of the vines must be worked by hand at every stage of the growing season, including harvest.  Yields for standard DOC Prosecco are permitted up to 180hl/ha, while the DOCG around Valdobbiadene limits production to 135hl/ha.

Torre Zecchei counts 15 hectares of vineyard holdings, and it also collaborates with a neighboring estate on an additional 15 hectares of vines, providing the equivalent of 30 hectares under direct supervision.  Average vine age is around 40 years, which is maintained by only replacing vines that have become too old or sick to continue production.  The manual harvest usually occurs towards mid-September, when potential alcohol levels are around 9.7%.  This is the ideal level for Prosecco, as even 10-10.5% is pushing the upper limits, for reasons we will discuss later.
After the fruit enters the cuverie, a pneumatic press slowly crushes the fruit, which generally lasts about four hours per session.  The first dose of Sulphur dioxide is administered here.  Alcoholic fermentation takes place in stainless steel vats and lasts approximately ten days, with one racking halfway through to remove the gross lees.  A second and final shot of Sulphur dioxide is applied after fermentation, which brings the total SO2 addition to a mere 40mg/L.

Over the next three months, the wine rests in steel tanks, with an occasional racking as needed.  A 15-day fining is performed through the addition of bentonite, and then the wine is filtered through a 0.45 micron tangential cartridge filter.  The base wine is generally through all of these steps and finished by February 1st.

To take the wine from the still base to frizzante, the Charmat method is employed, where a secondary fermentation in tank provides the pressure to the wine prior to bottling.  One of the outcomes of the Charmat method is a retention and emphasis on the freshness of fruit, with no effect of any aromatic material from the yeasts used for secondary fermentation.  In contrast, “Metodo Classico” spumante, also known as the classic Champagne method where secondary fermentation occurs in bottle, is actually partly dependent on the secondary fermentation yeasts to achieve the flavors that ensure the ‘house style’ is consistently produced.

To begin, the base wine is racked into a special tank called an Autoclave, which can handle high-pressure contents, up to nine atmospheres.  Yeast and concentrated grape must are added and the temperature is brought up to 17-18 degrees Celcius, which launches the secondary fermentation.  The reason for the grape must as the sugar source is actually political, as grape growers in the warm and “organized” southern provinces of Italy needed an outlet for their grapes that were too high in natural sugar to make reasonable wines.  In the middle of the 20th century, they used their influence in the government to make it law that all frizzante wines must use grape must for secondary fermentation.  “Metodo Classico” wines evaded this requirement due to the relatively insignificant volumes being produced during that era, so to this day, they may use cane sugar if they so choose.  The question isn’t necessary qualitative, however the mandate from the state for all Prosecco removes the option for growers in the appellation to use other types of sugar if desired.

bisson-glera-labelOver a period that lasts roughly 15 days, the temperature is lowered on the Autoclave as the pressure rises from the conversion of sugar to alcohol.  At the end of the process, the wine what will become Glera reaches nearly four atmospheres (atm) of pressure and adds about 0.9% alcohol to the wine.  The formula that is followed is 4g/L of sugar creates 1 atm of pressure, and it takes 16.5g of sugar to create 1% alcohol.  Thus by adding 15-16g of sugar to the base wine of 9.7% alc., the final wine arrives at 10.6% alc. with roughly four atmospheres of pressure.  The final element here is the question of residual sugar in the finished wine, as Prosecco is essentially never left completely dry, with zero residual sugar.  In fact, most commercial Prosecco runs on the sweet side, in the 12-18g/L of residual sugar.  We prefer a much dryer style and ask Bisson to limit sugar levels to 2-3g/L, which is among the lowest level found anywhere.  So for Bisson’s Glera, the level of sugar added for the secondary fermentation would be in the neighborhood of 6g/L, with 4g/L undergoing fermentation, then the temperature is brought down to arrest the fermentation, leaving the 2g/L in the finished wine.

To provide some context for the pressure differences in frizzante and spumante wines, the appellation laws consider wines up to 2.5 atm to be frizzante, while anything above 3 atm is spumante.  This puts Bisson’s Glera into an awkward place, as by the time it reaches bottle, the wine still retains about 3.5 atm of pressure, which is what Bisson says is required to maintain a finer and more elegant bubble.  To be considered spumante, the wine would need to be under a mushroom cork (ie. typical Champagne cork), which is not the case for the Glera.  So, we effectively have a spumante wine, labeled as a frizzante, though it conforms to neither set of guidelines as currently produced and packaged.  Let’s leave it at that and avoid getting the appellation board involved here.

After the wine finishes secondary fermentation, it is filtered again to ensure those last 2g/L of sugar are not put back to work with any leftover yeast.  Now the wine is in its final Autoclave tank and ready for bottling.  A hose connects the tank to the bottling line, then the bottles start to move while the pressurized wine flows from the tank into each bottle.  The bottles must be lowered to the same temperature as the wine (about 2 degrees Celsius) to prevent any bubbles from being released when the wine hits the glass.  Of course the bottling chamber must also be kept as a vacuum to keep the bubbles intact in the wine.  The crown cap is applied immediately, the bottles are labeled, and now ready to be sent around the world and enjoyed.

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