A little fizzy
I have had rosé and white wines with very low levels of CO2. They are not sparkling wines, nor as fizzy as a Vinho Verde. The wineries must inject CO2 at the filler bowl. How is this done? What CO2 level is sought? Thank you.
Many of our readers may not be aware that, indeed, for some wine styles and types, we winemakers actually add residual carbon dioxide gas (CO2) before bottling. A tiny bit of sub-threshold CO2 can actually provide a sensory “lift” or sense of freshness in the mouth, even if you wouldn’t necessarily call the wine bubbly. Dissolved carbon dioxide gas is easily dissolved in liquids, especially those that are cold (which is why a bottle of bubbly will go flat quickly if not chilled) and has a sensory threshold in wine of about 500 mg/L (ppm). When I’m bottling a white or rosé wine and I want a little lift, I try to bottle between 700–1500 mg/L.
This small level is accomplished in commercial wineries by chilling down the stainless tank with glycol to about 35–40 °F (2–4 °C), then doing a gentle pump-through (racking valve back to top of the tank usually works well) with an in-line sparging stone on the outlet side that is hooked up to a CO2 cylinder on a slow bleed. The level of CO2 can then be checked with a carbodoser (a simple glass cylinder that is sealed, shaken and released — the wine that gets released is a relative measure of the dissolved gas) or if you have access to a fancy lab, by a titration. I also find that, absent both, and if I’m working with non-production volumes, I just go by taste and how the wine feels.
If I had a barrel or two and wanted to get a bit of CO2 in there, I might do something as simple as stopping a malolactic fermentation with SO2 and then making sure I stored the wine cold and bottled while the wine was still young (say, within a few months of stopping the fermentation) and still had some dissolved CO2 in it naturally. You could also get a hold of your beer-kegging buddies and see if they would lend you their set up — I’d wager you could get a nice level of CO2 in pre-bottle wine (you don’t want too much!) with a keg and someone’s lagering fridge. The one thing you want to be careful of is overdoing it, because if you get much over 1 bar of pressure, especially if you can’t store your wine in a cool place, you’re going to start having corks popping all over your cellar.
You mention Vinho Verde, or the famous “green wine” of Portugal. Red, white or rosé, Vinho Verde isn’t a grape varietal, as some people assume, but simply means “young” wine. It is meant to be consumed within a year of bottling and frequently has less than one bar of pressure, sometimes called “pétillant” rather than “sparkling.” Vinho Verde usually is bottled with some residual natural CO2 gas in it and then sometimes bottled on a counter-pressure line to maintain the CO2 level through the bottling process. I would bet that your homegrown bottling process is much more gentle so you won’t need to invest in the equipment, just make sure you bottle your wine while it still has some dissolved CO2. Sterile filter for clarity and to exclude microbes (necessary if you have any residual sugar or malic acid).
If all of the crazy terms we use for pressure and fizziness have got you cross-eyed, here are some figures to use for conversion. Winemaking manuals will often be in one term or the other so it’s important to be able to convert between them to make any sense of it. Here are some handy conversions and gassy facts:
- 1 atm = 14.696 psi
- 1 atm = 1.01325 bar
- 1 psi = 261.33 mg/L (ppm dissolved gas measure)
- Sparkling wine is normally bottled between 60–90 PSI.
Sparkling to still?
Some of our wine turned from still to sparkling. Can we change it back to still at this point? Will nitrogen sparging take care of it or do we need to add sorbate?
Conway, South Carolina
Like I mentioned earlier, winemakers do have some control over how much fizziness we bottle our wine with. We can use a sparging stone in-line with a pump and hose (or in the bottom of a keg, if you have smaller amounts) to add carbon dioxide or, interestingly, we can sparge with nitrogen in the exact same way to remove dissolved carbon dioxide.
Sparging for carbon dioxide removal only works, however, as long as your carbon dioxide is not being constantly replenished by microbial activity. If you have an active fermentation going on, either from unfinished sugars from the primary fermentation, from an incomplete malolactic fermentation or from a microbial infection of any kind, no amount of sparging with nitrogen will remove the CO2 if it keeps getting produced. Before you sparge to strip out the CO2, you should determine if you just have residual dissolved gas or if it’s being created by an unwelcome source. If it is, you could “sterile” filter (through a 0.45 micron nominal pad or membrane), which just by moving your wine through the filter alone, may remove some of your dissolved CO2.
If you want to use nitrogen to strip out some of the dissolved carbon dioxide, I find it works best if my starting dissolved CO2 is under 2000 mg/L. The challenge with nitrogen gas is that it can also strip out aromas when you bubble it through your wine — it’s like swirling your glass repeatedly and liberating all of those nice smells you may actually want to keep in your wine. Sometimes I find that you can lose a lot of the carbon dioxide just by splash-racking (works well for young red wines especially, who can often use oxygen anyway at that stage) and moving the wine around the cellar. This doesn’t strip aromas nearly as much as a large sparging would. Of course, this doesn’t work for delicate whites that you may not want oxidized, in which case I would sterile filter, then proceed to sparge with nitrogen until the wine is at the level of dissolved carbon dioxide you desire. Don’t be afraid of using the easiest tool to degas: time. Often, if there is no microbial activity, a wine will lose all of its dissolved CO2 during the 12–18 months you may age it before bottling.
I’m interested in cold filtering to obtain alcohol-free wine. How is this done and what equipment is needed?
Alcohol removal remains a relatively infrequent process in the wine industry grand scheme of things, unless your bread-and-butter is selling de-alcoholized wine, like California’s Ariel brand. Removing alcohol from wine or any other alcoholic product these days either involves distillation (the alcohol is volatilized and then condensed, separating it from the wine) or reverse osmosis (ethanol passes through a membrane, removing it from the parent wine stream). The “cold filtration” method you mention is the one used by Ariel; they utilize a patented method that keeps the wine stream cool (under 55 °F/13 °C) while it passes through the reverse osmosis system. See the process, at http://www.clarety.co.nz/clarety/process.html.
A company in Sebastopol, California called Vinovation (www.vinovation.com) does offer reverse osmosis services for alcohol removal. They will do lot sizes as small as two barrels, but the cost is steep. Since two barrels fits well within their minimum lot size of 1,800 gallons (6,814 L), you’d be paying a lump fee of $1,700 for the privilege, not to mention shipping your two barrels to their facility and back.
Don’t get any ideas about distilling at home, either, because home distillation is illegal in the US and many other countries. Regardless of whether you’d want to use a traditional pot still or get your hands on a reverse osmosis set up (costing at least $150,000), you would still need a federal DSP (Distilled Spirits Plant) permit which, last time I checked, the feds aren’t handing out to the general public.
Not to rain on your alcohol-free parade, but from a sheer quality point of view, once you take the alcohol out of a wine, especially if you’ve cooked it as in a pot distillation, I think the result would be pretty much unpalatable. I respect the work that Ariel and other non-alcoholic brands do and the benefit they provide to those that want to feel like they’re drinking wine but may want to avoid alcohol, but for sheer gustatory pleasure I’ll choose a “real” wine every time. The reality is that removing alcohol from wine, and maintaining a drinkable end result (the de-alcoholized wine, not the booze) is almost impossible for the hobby vintner on any practical level. As you can see, the cost to acquire the equipment is high and the end results may not be up to your usual standards. If you simply must get your hands on some de-alcoholized wine, I would buy a bottle of Ariel (or Martinelli’s sparkling cider — long a favorite of mine) and save your wine for your friends and family that don’t mind a little ethanol.
UC-Davis graduate and professional winemaker Alison Crowe has been answering hundreds of your winemaking questions as the “Wine Wizard” since 1998. Her Wizard columns have been collected in The Winemaker’s Answer Book which is available at winemakermagstore.com. Do you have a question for her? Send your inquiries to: email@example.com. Unfortunately, Alison cannot respond personally.