Max’s article a while back about decanting wine got me thinking. I have seen a lot of weird sediment in wines over the years. Only some of it was backwash from swigging out of the bottle. There seems to be a number of distinct morphologies when it comes to junk floating around in a wine bottle. I looked into it a bit. The various types of sediment are not necessarily a flaw and just because you find certain things in aged wine does not necessarily make it a sign of a great bottle. Some sediments are a product of the winemaking process and others are a product of aging and storage temperature.
I had to educate myself a bit. I know the basics of how wine is produced but I wanted to get a better idea so we can take a look at where these funky bits come from. Every step in the process has the capacity to leave stuff behind.
Grapes are a pretty natural product. They come on woody vines that are grown on dirt. Wine grapes come with their own yeast in a thin film. Also bacteria, nematodes, spiders and all other sorts of agricultural organic-y stuff stuff. Really, grapes come pre-made with material that can end up in a bottle of wine. That doesn’t even take into account the things inside of a grape that can lead to sediment in your bottle. We will get to that in a bit.
Grapes are brought from the field to be crushed through a number of different methods. The crushing and destemming processes are fairly gentle but the mechanical action disrupts the skins of the grapes to release the juice and the destemming process will leave small bits of stem and pulp in the resulting juice. White wine must (fancy wine term for juice) is crushed with the stems and the juice is fairly quickly extracted. Red wine must is destemmed but the extraction process takes place later as the wine color and some flavors are due to longer contact with the skins. Sure, this is probably not the best illustration of the winemaking process but it illustrates how little chunks of stuff can be carried along further into the process.
The must is then fermented. Some are allowed to spontaneously ferment with the naturally occurring yeast and others are stabilized and fermented with a pure yeast culture that the winemaker can control. Yeast multiplies and during fermentation it flocculates. Flocculation is a natural action of yeast that causes cells to clump together. Usually these clumps get big enough to fall and lie on the bottom of the fermentation vessel in a thick cake. This mat can be very easily disturbed, stirring up small amounts of yeast. Again, another type of sediment that can find its way into the bottle.
Generally, a winery’s intent is to clarify the wine as best they can. The wine goes through “fining” in which some type of protein compound or fine clay like bentonite is introduced. These compounds bind tannins and other molecules that can cause haze and if allowed to make it to a bottle, can fall out of suspension and end up in your glass. Mechanical filtration is a method to prevent that. Easy enough, after fining, the wine is passed through a filter and particulate is removed. Some wineries make a greater attempt than others to get all of this out.
The most interesting sediment to me are colloquially known as wine diamonds. You will notice these in white wines more often than reds. They look like little sandy crystals in the bottom of your glass. If you get some in your mouth, they feel gritty and do not have much of a flavor. They will also nucleate on the cork looking like little tiny bits of glass. These are potassium bitartrate crystals. Tartaric acid is a major acid component in grapes and their juice. It is essential to the winemaking process as it keeps the juice at a nice hospitable pH for yeast while keeping spoilage organisms like bacteria at bay. This acid also
helps protect the wine during aging, while complex flavors and aromas develop. Under certain temperature conditions, this acid will react with potassium to form a salt that will crystallize and fall out of solution.
This is seen so commonly in whites because it happens below 10˚C. The chilling of a nice bottle of white will result in the precipitation of these crystals. Reds that are stored at a cellar temperature of 10˚C or less will also result in the formation of crystals. Mass produced wines and wines not intended for aging are often cold conditioned at the producer to get this to happen before bottling so that it will not happen on your table.
I should probably mention that I like and drink a ton of wine but do not consider myself a wine expert and I am not the best guy in the world to tell you how to choose your next case of vino. When I started this article, I assumed that sediments were a sign of less than stellar production or a failure to store the wine properly. I am happy that I was wrong about that.
The thing that I love about wine is that it is varied, strange, and hell of hard to figure out. A labor of learning, I suppose. Let’s leave it at this: Don’t count on sediment (or any other single factor!) to necessarily act as a guide as to the quality of a specific bottle you are about to buy. Wine diamonds or other sediment can be a sign of a better wine. At least one that was intended for aging, anyway. If you do see stuff in the bottle, avoid pouring it out into your lover’s glass. It is the nice thing to do regardless of how pretty those little crystals are.