Buzz: Hey, Marnie, I tried one of those pinot noir wines you were talking about last month, but I think there must have been something wrong with it. The color was so light it looked like it was made from sugared cranberry juice instead of grape juice.
Marnie: That's not unusual for pinot noir, Buzz. But it's certainly not a flaw. Most of the modern red wines we drink these days may look considerably darker and more opaque, but some of the world's best pinot noirs are so translucent you could read a newspaper through your glass.
Buzz: There you go again. Certain great wines look different from what you'd expect.
Marnie: That's because it's a grape with a thin skin. When it's crushed and fermented, the proportion of dark purple solids for each gallon of clear grape juice is lower than for thicker-skinned grapes, like cabernet sauvignon or shiraz.
Buzz: Wait, I thought white grape juice came from green-only grapes.
Marnie: That's true only if we're talking about the grape juice you can buy at the store, where "white grape juice" is clear and normal grape juice is inky purple. If you squeeze the juice out of fresh grapes of any color, it will run clear because grape pulp has no color – the color is all in the skin.
Buzz: That's something I should've known. Grapes are all alike – not white, pink, or purple – when you go to the heart.
Marnie: Commercial juice operations pasteurize their grape juice, which is like a cooking process that infuses color from the grape skins into the juice. This is a trick that companies like Welch's learned from making grape jelly. Because that striking purple color looks so much more appetizing than the grayish lavender you get from fresh-squeezed purple grapes, it has come to be the market norm. So much so that they take other steps, like steeping their grape solids in the liquid to maximize color extraction.
Buzz: I assume that means the kids have been drinking grape jelly juice this whole time.
Marnie: Sort of. In winemaking, the fermentation process fulfills a similar function. This is the stage of winemaking where living yeast cultures, like those used for making yogurt, convert the sugar in grapes into alcohol. When we make red wines, this process involves the grape solids and juice stewing together for two to four weeks while complex chemical reactions take place that generate their own heat. The length and temperature of this maceration determines how much color is transferred to the wine.
Buzz: Boiling for how they look and how they taste?
Marnie: Yes, but also the wide potential for color intensity that is limited by thin-skinned grapes, like pinot noir, which just don't have enough purple grape skins in each tank to make an inky-looking red wine.