Home winemakers use bananas, both dried and fresh, as a source of perceptible sweetness and body. Both effects are derived from the complex polysaccharides (that’s a fancy name for big, long-chain sugars) that bananas contain. By cooking the bananas or by using dried bananas (as many recipes specify), you’re taking advantage of these sugars to the maximum extent possible. Of course, adding bananas to your wines may impart some banana-like aromas and flavors – you just need to decide if this is correct for your type of wine. I would say it would be for, say, a late-harvest Muscat, but not for a bone-dry Bordeaux-style red wine.
I would use the banana trick for sweeter styles, as the amount of sugar added will be difficult to control. It would work well for sweet whites as well as sweet reds, especially Ports, when you’re concerned with getting sweetness as well as body into the finished product.
Using liquid pectin is a definite winemaking no-no. More often than not, it will contribute to unsightly hazes in finished wines.
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