In closing up a wine bottle, TPO (total package oxygen) is where the TLAs (three letter acronyms) are at, and the bottling operation is the bigger oxygen issue by far.TPO is the sum of dissolved oxygen (DO) in the wine plus oxygen in the air of the headspace (HO), and whilst many folk have got their heads around DO, theidea of TPO is still relatively new in wine industry.
Normal bottling processes entrant oxygen in the bottle. There is oxygen dissolved in the wine, and there is oxygen in the headspace. Our work shows that 60 to 70%of the total package oxygen is typically contained in the headspace. It’s typical industry practice to measure DO in wine, meaning the majority of the oxygen in the bottle is not being measured. In practice, this means QA specifications may state permissible DO levels at less than 1mg/l, but when you look at TPO,they may be closer to 3mg /l because they’re not measuring oxygen in the headspace. Wine specifications should be moving to detail TPO instead of the less relevant DO.
Measuring TPO has only been possible for a few years with the development of non-destructive(i.e. not needing to open the bottle of wine) measurement kits, such as The Pentair Haffmans Automatic InpackTPO. Standard laboratory equipment only measures DO.
Importantly,TPO is a snapshot measure immediately after the bottle has been packed. Three months after bottling. The TPO will virtually all be consumed by the wine. Itis from this point forward that closure OTR becomes the important factor in regulating oxygen intake into the wine. However significant quality and shelf life impacts may already have been incurred.
Management of headspace is therefore one of the most critical areas for control of oxygen ingress at bottling. Sometimes remedies are simple, though incur costs:using inert gases, for example nitrogen, or carbon dioxide, to flush out oxygen in the filling tanks, in pipework, the empty bottle, the headspace, prior tothe wine being transferred.
According to closure trials done on riesling at GeisenheimResearch Centre, Professor Dr. Rainer Jung found that after nearly a year,cumulative OTR varied significantly across screw cap and synthetic, from “0.5 to2.5 mg/l in total, which is not very much. It is not enough to oxidise the wine.”
But a different picture emerged with headspace trials. Jung said “we measured 6mg/l oxygen in the headspace. It takes about 4mg/l SO2 to reduce 1mg/l oxygen, so if you have 6mg/l of oxygen, you need 24mg/l SO2.” The first AWRI closure trial identified oxidative characters developing in white wine at about 10mg/l freeSO2, and whites are commonly bottled with 30 to 40mg/l free SO2, so, said Jung“if you don’t want to lose of 24 mg/l SO2, flush the headspace [with inert gas].”
Jung highlighted the snapshot significance of DO and TPO, saying wine can arrive atthe bottling line with 1-2mg/l DO already in the wine, though this completely depends on what has happened to the wine before, and its style. For example amicro-oxygenized red versus a reductively made sauvignon blanc. And he said, of a reductively made wine, where oxygen has always been kept away “in the last step, you pump into the bottling tank, and get the same amount of oxyge nuptake. This will directly react with wine components, so no DO is measured,but the aromatics and phenols can be oxidized.” So the wine is in specification, but its defining characters have been lost. Even some reds won’t benefit from oxygen at bottling.
Headspace management is also a critical control point for traditional method sparkling wine. Michel Valade, responsible for viniculture at the CIVC in Champagne said “the quantity of oxygen that might enter the bottle at moment of disgorgement varies according to conditions of disgorgement.” CIVC studies showed that the amount of oxygen introduced at disgorgement varies from 1 to 10 mg/l, and averaging 2 to 4mg/l. Valadesaid that during ageing [sur lattes] “only 1 mg/l per year of oxy genenters the wine, and is consumed by the wine, so 2 to 4mg/l is the equivalent of 2 to 4 years of oxygen transmission through the closure.”
Valade explained “at the moment of disgorgement some bottles let some mousse escape,in which case there will be no oxygen entering the bottle [as the effervescence expels headspace oxygen]. But if bottle is very quiet, or stays a bit longer onthe line, up to 6 mg/l may enter the bottle.” This clearly creates big bottle variation which will directly affect the flavour profile.
The level of TPO that industry should be aiming for depends on individual wine style, though“generally the lower the better” said Roget. Vidal said their studies showed“on average, DO is 1-2ppm mg/l. And headspace is 1-4mg/l, giving a TPO of 2 to 6mg/l.” So, he said “A TPO of 2 mg/l is therefore already a good situation – a bottling line that is working fine.“
For the majority of wine which is drunk within two years of bottling, this is all crucial, as high TPO at bottling quickly erodes shelf life. And for these wines, the wine should be ready for drinking at the point of bottling. Jung said “During bottling and storage the lowest quantity of oxygen coming into the bottle would be the best way to keep the wine in a ‘ready to drink’ situation.” Roget added “a high TPO can have ashelf life reduction equivalent to 10 years of oxygen transmission through a Saran-tin screw cap.” He said it’s a “completely different order of magnitude with TPO versus OTR.”
