You can't taste the vodka, yet the sauce tastes different without it. Here's what the alcohol is doing to the tomato and cream, and how much of it is still in your bowl.
Why you don't taste the vodka
It's built to be neutral. Vodka is basically ethanol and water, distilled and filtered until there's almost no flavor of its own. It doesn't bring a taste to the sauce the way wine or whiskey would. High confidence
It's heavily diluted. Half a cup of vodka in a quart of sauce works out to only a few percent alcohol, even before any cooks off. High confidence
Simmering drives a lot of it off. But not all of it. After 15 minutes, roughly 40% is typically still there (use the calculator below). High confidence
What it changes in the tomato and cream
A bit of "bite" that cuts the richness. The leftover alcohol adds a faint sharpness and warmth that keeps heavy cream from tasting flat. This is the effect cooks most consistently notice. Medium confidence
It lifts the aroma. Ethanol is volatile and helps carry aroma molecules up to your nose as the sauce steams, so the tomato smells brighter. Medium confidence
A "bridge" solvent. Ethanol mixes with both water and fats, so it can dissolve flavor compounds that water alone handles poorly. Tomato contains many of these, and ethanol may help spread them through the sauce. Lower confidence
The cream stays smooth. Ethanol may help the fat and acidic tomato stay blended. Most of that work, though, is done by the cream's own proteins and fat. Lower confidence
How much alcohol is left in your sauce?
In tablespoons. 8 tbsp = ½ cup, typical for one pound of pasta. Assumes 80 proof (40% alcohol).
0 = stirred in and taken right off the heat.
Tomato, cream and everything else, in cups.
Alcohol remaining
--%
Of what you poured in
Sauce strength
--% ABV
Alcohol per serving
-- g
Pure ethanol
Per serving
--
US standard drinks (14 g each)
Cooked off--All still there
Fun fact
"The alcohol all cooks off" is a myth. In USDA measurements, a dish simmered for 15 minutes still held about 40% of its alcohol. It took about 2½ hours to get down to 5%. Alcohol and water evaporate together, so the alcohol leaves gradually rather than all at once.
Contrarian view
In blind tastings, many people can't reliably pick out the vodka version. And the "unlocks hidden tomato flavor" story is far more often repeated than measured. A fair reading is that vodka makes a subtle difference, mostly a slight sharpness. You could get a similar lift from a squeeze of lemon, a splash of the pasta water, or a pinch of chili flakes. If you're cooking for kids or someone avoiding alcohol, leaving it out costs you very little.
How the calculator works
ethanol added (mL) = tbsp × 14.79 × 0.40
ethanol left = ethanol added × retention(simmer time)
sauce ABV = ethanol left / (sauce volume + vodka volume)
grams per serving = ethanol left × 0.789 / servings
Assumptions
Retention follows the USDA table for alcohol stirred into a mixture and simmered, with straight-line interpolation between its time points. The 0-minute value uses the USDA figure for alcohol added to a boiling liquid and taken off the heat (85%).
Real retention depends on pan size, heat, whether it's covered and how much you stir. A wide, uncovered pan at a strong simmer loses alcohol faster.
Sauce volume is treated as constant. In reality water evaporates too, which slightly concentrates what's left.
The confidence labels above reflect how well supported each claim is, from well-measured (retention) to mostly kitchen lore (emulsifying).
Sources
USDA (2007). Table of Nutrient Retention Factors, Release 6. Alcohol retention by preparation method.
Augustin, J. et al. (1992). Alcohol retention in food preparation. Journal of the American Dietetic Association, 92(4), 486–488.
NIAAA. What is a standard drink? (14 g of pure alcohol in the US.)