As I set about to run some trials in disgorging and adding dosage to riddled bubbly—two critical steps in the méthode champenoise (aka traditional method) production of bottled-fermented sparkling wine—I was reminded of an interesting question asked by an attendee at my seminar at the last WineMaker Magazine Conference in Napa Valley: “Why not simply place bottles upside down in carton boxes instead of having to riddle each bottle every day for 21 days?”
Tough question to answer without looking at the physics of what is actually happening during riddling—the process of channeling bottle-fermentation lees down to the neck portion of the upside-down bottle to allow the lees to be expelled by disgorgement and produce a crystal-clear bubbly. A poorly riddled bottle can spell disaster, and turning bottles over to let the lees flocculate without proper riddling simply won’t work.
If bottles are turned over in a case, yes, most of the lees volume will find its way to the neck; but “most” is not good enough. The problem is that some lees particles will cling to the glass—just hold up the bottle against a strong light source and you will see what I mean. These fine lees particles now become nucleation sites for the dissolved carbon dioxide gas. Once the bottle is disgorged and the lees are removed, microbubbles will rapidly form and nucleate at these sites, and then quickly rush up to the surface of the wine in the bottle, and cause the wine to gush out uncontrollably. This is further exacerbated when adding the dosage.
Let’s look at this phenomenon a little closer.
Carbon dioxide gas exists in dissolved form in sparkling wine, and the pressure exerted in the closed bottle causes the gas to remain dissolved; however, according to Henry’s law, as soon as the cork is pulled, the higher gas pressure in the wine will slowly work towards equilibrium with the atmospheric pressure just above the surface of the wine. (This is the same phenomenon as when opening a can of soft drink; after several days, depending on temperature, the drink goes flat. Henry’s law more specifically states that, at a constant temperature, the volume of gas dissolved in a given volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.) As the gas and atmospheric pressures slowly move towards thermodynamic equilibrium, carbon dioxide gas becomes less soluble and causes bubble nucleation, or the formation of microbubbles, in nucleation sites. Any imperfections in the glass, such as scratches or residues, as well as microscopic colloids still in suspension in the wine will hasten bubble nucleation and give rise to continuous streams of rapidly forming tiny bubbles dancing endlessly to the surface of the wine. Bubbles then burst into tiny droplets to release all those delightful aromas. And that’s the reason why sparkling wine flutes washed with detergents tend to show fewer bubbling activity—the detergent will “seal” glass imperfections and reduce the surface area of nucleation sites. But if you have too many imperfections and considerable lees still in suspension, the result is excessive gushing and wine loss.
By riddling the sparkling wine according to the traditional method, the riddling aid, added just before bottling the wine for bottle fermentation, will help bring down the lees to the neck of the bottle. The bottle rotating and tilting procedure on riddling racks causes the riddling aid to “sweep up” up the lees from the side of the glass and help it move down to the neck. When done properly, the sparkling wine should be crystal clear with no visible particles on the glass when the bottle is held against a strong light source.
Ah! How clever those Champenois pioneers were!!
If you want to watch a short video of how we disgorge bubbly at Maleta Winery, click here.