Greetings from the future (I'm writing from the MW seminar in Adelaide)!
Honestly, I was planning on "phoning in" the upcoming TAMS and writing on the topic of technical considerations at bottling. And then I stared at a blank screen for a while as I realized that it wasn't as easy as I had originally thought.
Has anyone tackled this question yet Outline the key technical considerations involved in the final packaging for wine. (2015)
In my opinion, the main considerations include (but are not limited to)
Does anyone have notes for these or other considerations?
Kelli White Sarah Bray
Here's what I wrote for my most recent TAMS.
An introduction (not included here)
Microbial stability is essential to ensure that yeast and bacteria do not bloom in bottle. This is especially important for wines which are bottled with residual sugar or malic acid. To ensure microbial stability, the majority of the world’s wines by volume are bottled after sterile filtration on the bottling line. Integrity of the sterile membrane can be tested by a bubble point test where gas is pushed through the membrane before the line is run. At Taylors in Clare Valley, wines for Aldi are rough filtered down via cross flow and sterile filtered with a 0.45 micron absolute membrane on the bottling line. In contrast to this, at Koerner in Clare Valley, all wines are sugar dry and undergo full malolactic fermentation to remove nutrients for microbes. These wines are bottled without filtration as the brand is aligned with the natural wine movement. Both Taylors and Koerner are internationally distributed and show stability in the marketplace.
The temperature of the wine impacts dissolved gas levels and label adherence to bottled products. As liquid temperature decreases, the wine has a greater ability to pick up and hold dissolved gasses including oxygen which can impact ageability. If the wine is too cold compared to ambient air temperature, the bottles can “sweat” and paper labels may not adhere properly.
Dissolved oxygen levels directly impact free sulfur dioxide concentration. 1 mg/L of dissolved oxygen will oxidize 4 mg/L of free sulfur dioxide. This is especially relevant for low pH wines destined for early consumption, where the wines are bottled at low levels of free sulfur dioxide. Sevenhill Cellars in Clare Valley releases a low pH Riesling less than a year after vintage. To manage dissolved oxygen, the winemaker adds ascorbic acid at transfer and before bottling. However, other wineries including College Cellars in Washington, USA uses nitrogen sparging.
Wines should be bottled at a free sulfur dioxide concentration that ensures their freshness at the desired time of consumption. The exact concentration will be dictated by the complex relationship between pH of wine, closure oxygen transfer rate, and desired time of consumption. However, most table wines are bottled at levels between 20 and 35 mg/L of free sulfur dioxide. To ensure that the wine was fresh in all domestic and export markets, the 2015 Caymus Napa Valley Cabernet Sauvignon was bottled at 30 mg/L of free sulfur dioxide.
Ultraviolet (UV) light exposure can cause sulfurous off aromas as sulfur containing amino acids are transformed into aromatic compounds. To preserve aromas in wines designed for long term ageing, wines can be bottled in darker glass which helps to block UV light. Amber colored glass will block 90% of UV while clear flint glass will block only 10%. Bonneau du Martray Corton Charlemagne Grand Cru is bottled in amber glass, and at approximately $250 USD is a collectors wine for ageing. Matua Sauvignon Blanc is bottled in clear flint glass and at $12 USD is destined for immediate consumption.
Closure oxygen transfer (OTR) rate is arguably the most important consideration for freshness and ageability of wine. According to the Australian Wine Research Institute, high quality long natural corks and screw caps with saran-tin liners have similar OTR - 0.002 ppm/day vs 0.001 ppm/day. However, long natural corks have the natural variation of cork bark and the OTR may not be consistent from cork to cork in the same lot. For producers who want a known and guaranteed OTR with a cork closure, Diam agglomerated corks are synthesized for consistency. Their OTR is 0.3 ppm/year on all products. Hugel in Alsace uses DIAM 30 on Grand Cru wines which guarantees this OTR for 30 years on their most ageable wines.
Conclusion (not included here)