I brewed a single 10g batch of base beer, then split it in half after primary fermentation. 5g was racked onto previously-frozen Maine blueberries. The other half was racked onto a strawberry/rhubarb/brown sugar mix. It was 2:1 previously-frozen whole strawberries to fresh rhubarb, and the rhubarb had been roasted with the sugar to caramelize a bit and take the edge off the harshness. The first half stayed on blueberries for just one week, while the second was on fruit for two weeks.
Both finished beers were kegged, force carbonated to the same level, and served from the same fridge. The Blueberry beer actually has a serving line at least 4ft longer than the S/R. However, the S/R has almost no head when poured and the blueberry pours with almost half a glass of foam.
Does anyone have any ideas what might cause this big difference? Seems pretty strange to me - the only difference was fruit and simple sugar.