Ever drink a glass of really good wine and find little crystals at the bottom?  These are “wine diamonds,” not sediment, and they have been helping to preserve your wine!

Potassium hydrogen tartrate is a byproduct of winemaking. In cooking, it is known as cream of tartar.

Wine diamonds are, in actuality, potassium bitartrate crystals that sometimes form on a wine bottle’s cork, most often when chilled.  During the winemaking process, itself, they naturally form on the sides of fermentation tanks.  They can be found in both red and white wines, and do not in any way mean that there’s a problem with your wine.  In fact, when present, they help lower the pH, making a hostile environment for many types of bacteria that can spoil wine, helping to preserve wine after fermentation.

The majority of winemakers, however, have gone to great lengths to eliminate these crystals from their bottles.  (Mostly, this is a reaction to complaints about the harmless crystals.)  Very cold stabilization before bottling (usually between 2 or 3 weeks) is a “solution” that brings these tartrate crystals to the fore, allowing them to be easily filtered from the wine which is then warmed back up.

If you do find wine diamonds in your wine, your wine was probably made very naturally, and this is a good thing!  Also note that consuming the crystals will not harm you; these wine tartrate crystals are the very same ingredient in the cream of tartar you used for baking the other day.  They’re also used in a bunch of other foods and nonalcoholic drinks.  It so happens that wineries are the only commercial sources for tartrates, and they often collect and sell wine diamond deposits that form in their tanks.

So, the next time you see a few crystals at the bottom of your wine glass, know that they have occurred naturally, are nontoxic, and that they have helped to preserve your wine.  Cheers!

Today, most red wines are produced using a process similar to this one…

First, a vintner decides when the grapes are ripe.  This is done by taste, concurrent with today’s technology of taking accurate sugar readings.  The grapes are then harvested and placed into a machine that removes their stems.  The machine also crushes them (without pressing them) so that A) the grapes become exposed to yeast and B) the skins will color the wine.  The yeast then transforms the grape’s sugar into CO2, heat, and alcohol; this is fermentation.  The crushed grapes and liquid then sit (macerate) until it is decided that the taste is ideal.  During this process, the grape skins often float above the liquid.  Since these skins must remain submerged, for best results, they are repeatedly pushed back into the liquid, or the liquid is mechanically pumped over them to continually submerge them.  If the grapes sit for too long in this state, the wine will taste bitter.  If they do not sit long enough, the wine will taste too weak.  The vintner determines when enough time has elapsed.  Once the decision has been made, the liquid is removed and the solids are sent to the press.

A Mechanical Wine Press (image from Wikipedia)

A mechanical press squeezes out the remaining juices in the solids.  This, too, is a delicate process; pressing too firmly or too frequently produces a poor quality wine.  After this, the wine needs to settle; transferring the wine from barrel to barrel after settling helps to separate/filter out solid matter and other particles that may cloud the wine.  Following this, a malolactic fermentation stage is often the next step in red winemaking.  Here, a wine’s malic acid is converted into CO2 and lactic acid.  Basically, the process reduces a wine’s acidity by organic rather than chemical means.  (Certain wines like Gewurztraminers, Reislings, Ehrenfelsers, and others that depend upon malic acid to enhance their flavors do not go through this step.)

After an aging process, the length of which is determined by the type of wine, fining and filtering processes remove sediments from the wine.  The wine is then bottled carefully to avoid contact with the air. (And, as we know, many of the best bottled wines are stored for several years before they are released to us!)  For more fascinating information about winemaking and wine technology, check out Vintage Cellar’s Wine Storage Education Center.  There, you’ll find more tantalizing trivia and wine storage tips to think about.  Cheers!

Today, the media reported that archeologists in Armenia have unearthed the world’s oldest known winery.  They think that the 6,000-year-old winemaking equipment, which includes a wine press and desiccated grape vines and seeds, was used to make special wines for funeral ceremonies held nearby.  Very cool!

Read the full story on Time.com here.

Dave Breeden discusses the art and science of winemaking from Scienceline on Vimeo.

During the harvest season, I got the chance to interview New York winemaker Dave Breeden. Dave is a chemist and a philosopher who makes award-winning wines at Sheldrake Point Winery in the Finger Lakes area. The question I came to Dave with was, “Is winemaking an art or a science?” His response was fascinating. Watch the video above and read the full profile here.