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I have had rosé and white wines with very low levels of CO2

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George Vierra — via email asks,
Q

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.

A
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