You might be familiar with hearing your wine maker say “Don’t forget to gas your tank before starting the job” or seeing ‘Co2 cover’ on your job note. It is something we all get told and must remember to do when working with wine. But why? What are we really doing?
In this blog we will talk about oxygen, understand how we can use it for good and look at how we can minimise its negative faults on our wine. For the sake of definition, I found the following statement made by Bryce Rankine easy to relate to “Aeration is the physical process of dissolving oxygen in the must or wine, while oxidation is the subsequent chemical process of oxidising the juice or wine constituents.”
When we talk about Oxygen in the cellar, what we are really looking at is Dissolved Oxygen and oxidation. Dissolved Oxygen or DO is the “concentration of oxygen molecules in a liquid,” and we are concerned with how much is in our juice, must and wine. Wine is saturated at 6-8ppm while must and fresh juice has a high capacity for utilising Oxygen so can be completely saturated (which is why we gas cover wine, and not juice at harvest). You could say using it in the initial stages of wine making is far safer than the later. Some positive ways we can use oxygen in early wine making processes include: Gentle aeration to ‘blow off’ H2S aroma, having plenty of Oxygen and Nitrogen available to yeast to propagate a healthy culture and during the exponential growth phase. We also use oxygen to our advantage in red wine making to extract and stabilise colour and soften tannin during ferment and in-between primary ferment and malolactic conversion. Some wine makers also use a technique called Hyper-oxidation. See more on this here: Hyperoxidation: White winemaking jujitsu
So, what about in wine then? Well, when oxygen and wine get together the effects can be less desirable and this is when we start to see problematic oxidation. To combat this, we start displacing O2 with CO2 or another inert gas like argon or nitrogen (CO2 or dry ice is common so I will just use that as the example from now on). Displacing simply means we take away oxygen and replace it with CO2. Since CO2 is heavier than O2 it falls to the bottom of the vessel, or line etc. and pushes all the O2 out, blocking the O2 from interacting with the wine. Also, make sure there is free Sulphur present to preserve the wine as it is an antioxidant and has antimicrobial properties.
DO will work its way into wine when and wherever it can: during racking/transferring, filtering, storage, bottling and cold stabilisation. To combat this, in the cellar we ‘gas’ the receival tank and the head space of the tank we are emptying, undertake ‘gas rounds’ weekly on storage tanks, fill lines with CO2 before starting a job, ensure seals and valves are done up tightly, sparge the wine with nitrogen before bottling and routinely check free Sulphur’s. I feel there should be a special mention here in relation to Cold Stabilisation: DO is dissolved into wine more readily at cold temperatures so it pays to check your SO2 levels in relation to your pH levels before you start this process, especially if your wine has a high pH.
At this stage you might be thinking that we have left out one key element when considering oxygen in wine making, and you are right, we have! Barrels, and to a degree amphora and concrete vessels! These three mediums allow wine to “breath” while in storage. Each has its own rate of micro-oxidation and characteristics it will impact on the wine. So long as you keep the vessel full/ topped and the free sulphur up, these are a great way to ‘age’ your wine before bottling. Very common for red wines.
So, there you have it folks, the basics in understanding the relationship between Oxygen and wine in the cellar. There is so much more we could go over here, such as how to measure DO (using a electric membrance sensor, luminescent/optical sensor probe or spots), which cellar activities pick up the most DO (tank to tank transfers), inline sparging (use nitrogen to protect wine while its moving), and bottling (what’s better, screw cap or cork?) but time is of the essence. If you are interested, ask your wine maker what your company strategies and thresholds are for DO or further reading is available here: Strategies to Manage Dissolved Oxygen
Better cellar handing everyone.
Join me next time when we will take a more in-depth look at the nasties causing Oxidation.
Steiner T. E. (August 2013) Strategies to Manage Dissolved Oxygen- How to identify practices that prevent unwanted oxygen absorption in wine. https://winesvinesanalytics.com/features/article/119752/Strategies-to-Manage-Dissolved-Oxygen
Rankie B. (1989) Making Good Wine. Sun Books. A manual of winemaking practice for Australia and New Zealand. Pg 187
Ruis A. (n.d) NMIT, CCO410 Wine Finishing and Analysis, S2-20 ‘Winery Oxygen Managment’ PowerPoint slide show