A Chromatogram is a test typically done in winemaking to determine if malolactic fermentation has finished. In essence, you begin with a sheet of special paper. You hang the paper from one end, and put drops of wine at the bottom. There are channels running top to bottom in the paper, and as you know from spilling wine on paper towels, wine tends to get soaked up by the paper. So the wine begins to soak its way up the channels, moving against gravity.

Different types of acid have different weights. Tartaric acid is very heavy and therefore doesn't tend to soak up the paper very high. Malic acid has a medium weight, and tends to soak its way halfway up the paper. Lactic acid is very light, and can soak all the way up to the top of the paper.

Since malolactic fermentation is all about having the wine's malic (apple style) acid get converted into lactic (milk style) acid, by doing a chromatogram you can see visually where the wine is in the process. If there is a big spot in the middle of the paper, you know that the wine is mostly malic acid and is still being converted. But if there is nothing at all in the middle of the paper and a big spot up at the top of the paper, you know that the wine is full of lactic acid and that you are all set with the fermentation.

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