Along with the Merlot toss in a little Cabernet Savignon and you'll have a Super Tuscan blend. Not really, you'd only be adding 750ml or so to 23L, that's hardly enough to change much. I don't worry so much as to the variety of my red top up wines as I do the quality. I only top up with wines that I think are as good or better than what I am making. Some folks will disagree with me but I want my top up wine to enhance what I'm making. 75% of the time my top up wine is something I have made myself now. But IF I use commercial wine for top up it's pretty darn good wine that I would serve myself or friends.