If I am serving a series of different red wines using a decanter, should I wash out the decanter between bottles or simply rinse with water? Or should I do nothing and pour the new bottle into the decanter?
Laziness is highly underrated sometimes. The answer is: Do nothing.
Chlorine from tap water can adversely affect the new wine, more so than the residue from the previous bottle (though we're talking about subtle effects). Soapy residue is worse, so I wouldn't take the chance of washing out the decanter. Simply drain as much of the first wine as possible, then pour in the next bottle. You won't be corrupting the second with flavours of the first if a few drops remain in the decanter.
If the first wine has left visible sediment, you may want to consider rinsing with plain water. But you shouldn't have much residue in the decanter in the first place.
There are two reasons to decant a wine. The first is to aerate so that oxygen can soften the wine's astringent tannins and amplify its fruit flavours. The other is purely aesthetic – to pour an old wine off its sediment. After many years, some red wines develop harmless residue, which precipitates out of the liquid and down to the bottom of the bottle (assuming you've moved the bottle from the horizontal cellar position to the vertical position at least eight hours before serving, which is recommended). Old wines should be decanted slowly and in good lighting conditions. This will allow you to ease up on the pour just before the sediment can make its way into the decanter.
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