What's with the sediment in my wine?

A lot of people probably have questions about the sediment at the bottom of a bottle of wine.  What is it exactly?  Is it good?  Is it bad?  Should I drink it?

Well, these questions are all complicated.  In short, sediment in wine comes from many sources.

Sediment can consist of debris from the winemaking process, lees (dead yeast cells), and tartrate crystals, or, usually, some combination of the above.

Wine is naturally a hazy substance.  The yeast which has created the alcohol is suspended in the wine, as are tiny particles of grape skin, pips, seeds, etc.  Many wines are filtered or fined to remove sediment, although, unfiltered and unfined wines are becoming more popular for several reasons (biodynmic and vegan winemaking, health concerns, and a healthy respect for more natural wines among them).  Moreover, the process of filtering out or, especially, fining out "undesireable" sediment can also remove things which positively affect the way the wine develops with age.  This is why white wines, and red wines meant to be drunk young, are more often filtered or fined.

Moreover, as wine ages, tartrates crystalize in the wine, particularly if the wine is stored in or transported in, cool temperatures.  These are perfectly harmless, but not temperature stable, substances found in all wines.  As the wines chill, they crystalize and fall to the bottom of the wine.  Barrel aging wine allows many tartrates to crystallize before the wine is bottled, but wines which are bottled young have more tartrates to crystalize.  Many winemakers "cold stabilize" their wines, chilling them and removing tartrate crystals before bottling the wine.  Like filtering and fining, the problem is that you can also filter out many things that contribute to desireable changes during bottle aging.  So, again, this is much more common in wines meant to be consumed in their early years.

As far as if sediment is good or bad, the answer is really neither, but leans toward good, particularly n older wines.  Sediment is perfectly harmless, and the compounds in the sediment, particularly grape remnants and lees, can contribute great flavors to wine as they age.  As far as if you should drink sediment, the general feeling seems to be no.  This is the main reason to decant wine (as opposed to aerating it, which also involves putting it in a decanter).  By carefully pouring the wine into the decanter, and by again, carefully pouring from the decanter to the glass, you can avoid most, if not all, of the sediment.  If a little sneaks into the glass, though, it's not the end of the world.  I think for the most part, the aversion to sediment is more of a personal taste, and based primarily on texture, especially since sediment settles at the bottom of the bottle and glass, so the last sip of the last glass poured would have quite an interesting texture to it.

What Exactly is Malolactic Fermentation???

Wine geeks and professionals often use terms that can be difficult for the casual consumer to understand.  Usually, though, at least the major point of the words, can be broken down pretty simply.  One example of that is malolactic fermentation, which I'm going to try to break down pretty simply and then at least at an introductory scientific level.

The easiest way to understand malolactic fermentation is to actually look at the words themselves.  Fermentation is the action of yeast converting sugar into alcohol and carbon dioxide, at least at the most basic level that most of us drinkers need to/want to know about.  The reality of it is, much like our own digestive process, or any other chemical reaction, there's a lot more going on.  In the case of malolactic fermentation, one of the results is the conversion of malic acid into lactic acid.  Hence the name malolactic fermentation.  Malic acid is the tart acid which tastes a lot like a green apple or tart pear.  Lactic acid is the acid found in milk, butter, and other dairy.

So, on its most basic level, malolactic fermentation is fermentation which turns tart, apple-like acids into creamy, buttery, acids.  Chardonnay is the varietal where this simple breakdown is most evident, and most easy to understand.  On the other hand, malolactic fermentation is either desired, or not desired, in many other varietals, which neither start out with such a sharp green apple taste, or end up quite as buttery as many chardonnays do.

The Science Behind It
Malolactic fermentation usually uses one or more of three different types of bacteria, Oenococcus oeni, Lactobacillus, and Pediococcus.  Each of these bacterias eats up tart malic acid and spits out lactic acid and diacetyl.  Lactic acid provides a smooth, creamy, round flavor and mouth feel, and diacetyl, which is often considered a fault in both beer and wine, provides a buttery flavor and aroma (think movie theater popcorn).

Again, Chardonnay is the most extreme example, but most red wines, and many whites, undergo some malolactic fermentation.  The original flavor profile of the wine, the environment in which malolactic fermentation occurs, and many other factors affect how obvious the flavor effects are on a wine.  On the other hand, many crisp, tart, fruity, and floral whites are produced in such a way as to almost eliminate the possibility of malolactic fermentation, in order to preserve the sharp acidic notes in the wine.

Malolactic fermentation can occur either as part of the primary fermentation, or after the wine has been fermented.  It can and does occur naturally, or the bacteria can be deliberately introduced.  It is almost always done either during fermentation or aging, and almost never in the bottle.  One increasingly rare exception is certain Vinho Verdes from Portugal, which underwent malolactic fermentation in the bottle, since slight effervescence is expected in the wine.  This is less popular now, as wines which undergo fermentation in bottle also throw a sediment and pour less clear.

Hopefully this post helps a few people understand a little more exactly what malolactic fermentation means, and more importantly, why they should care about it when buying or drinking wine!