Why does pouring carbonated beverages onto fruit cause them to fizz? I have noticed that making mimosas, the champagne fizzes more than just pouring it into a flute. Likewise, pouring beer onto citrus fruit or strawberries fizzes a lot. My theory is that the pH drop associated with the acidic fruit causes the solubility of CO2 to decrease and hence, the fizz. Can anyone verify this?
All carbonated drinks are oversaturated solutions of $\ce{CO2(g)}$. Pouring over fruits lead to contact with many residual air bubbles, which serve as  fizzing places for $\ce{CO2(aq) -&gt; CO2(g)}$. 

It is more or less the same as the ( previously already opened ) drink shaking, where violent fizzing occurs as well.

It is a similar process activation, like if you bend the activation chaff in a pocket heater with molten $\ce{CH3COONa \cdot 3 H2O}$, or if you pour overcooled water from a freezer ( see YouTube ) and watch fast ice growing.