Ignore if you're completely bored by winemaking details, or if you want to complain about my sloppy process with paper chromatography.
Here's a picture of the progress of malolactic fermentation in the barrels of 2010 Vincent Pinot Noir. That's where sharp malic acid in young wine is converted by good bacteria to smoother lactic acid, a key part of the elevage or maturation of wine in barrel. As soon as "ML" is done, most people add some sulfur dioxide to help keep the wine smelling and tasting fresh until bottling. So it's important to monitor the progress. You don't want to add sulfur too early, and you don't want to wait too long to add it once the process is complete.
What does this picture tell us? At the bottom there are markings where drops of wine from each individual barrel or tank were dried on the paper. Then the paper was rolled up and soaked for several hours in developing solution, much like one would do with camera film. Then you let the paper dry or develop and here's what we see. The lowest strip of yellow is where the wine drops where. The next strip is strong evidence of tartaric acid, the primary acid of any grape wine. Then next portion up is where malic acid shows up. Mostly, it looks like ML is pretty much done, maybe not barrel 6, and a few others show some faint traces of malic acid. Then at the top the yellow strip shows lactic acidity. That shows up strongly in every barrel (there is no barrel number 2, so that's why that column doesn't show much of anything).
At the start, there was no lactic acid, only tartaric and malic. So things look pretty complete. The next step is to test the lagging barrels again, or perhaps test them at a commercial lab for precise levels of malic acidity. Once everything is definitely done, in goes some sulfur and the wines rest for several months to settle out and continue to evolve. And thankfully, because wines in barrel in the middle of ML taste weird. I'm ready to see what we really have with the 2010 vintage. Lots of promise, but like rockets when they used to go behind the moon, it's time to reconnect and see where things are.