One of the reasons that winemaking is referred to as an art as well as a commerce is that so many things can go wrong during the life span of a wine in production. Aside from mechanical problems like leaking barrels or cellarmen running into tanks with forklifts, wine is chemically delicate and must be supervised and nurtured, like a child, in order to avoid the various infections and diseases to which it might be prone. On top of that, winemakers use some pretty unusual ingredients to get the wine ‘just so’.

Egg white1. Egg whites

That’s right. Slimy, uncooked egg whites. Egg whites are used to catch floating microscopic debris in the wine that is making it cloudy. They are also used to remove excess tannins or even smoke taint from wildfires. This is a process called ‘fining’.

So if you see flats of eggs stacked up in the cellar, they’re likely not for brunch. It might take 300 eggs to fine an 8,000 gallon tank.  The winemaker separates the whites from the yolks (that’s the part that will end up as a meal for the cellarmen), whips them lightly, carries them to the top of the tank and slowly spreads the whites over the surface of the wine. The whites sink through the wine, attracting micro-particles and sticking them to the bottom of the tank. The clean wine is then racked off and the egg white sludge is washed out of the tank.

Egg whites are considered one of the gentlest fining ingredients in wine, which is why they’re frequently used.

Bulls blood2. Bull’s blood

This is really old school, and thankfully, illegal in the US and France—but while uncommon in other countries it probably is it not illegal.  Like egg whites, blood has historically been used as a fining agent because the proteins are what attract tannin molecules and sediment. There’s even a famous wine in Hungary called Bull’s Blood. (But don’t worry, there’s no blood in it. Probably.)

sturgeon bladder3. Dried sturgeon bladder

Better known as isinglass, dried and powdered fish bladders have been used to thicken jams, jellies and pastry creams since at least the 18th century. It was also used as a clotting and healing ingredient in old-fashioned “court plasters”, a precursor to “sticking plasters” and our modern Band-Aids.

While its high protein content makes it ideal for clarifying beer and wine, it’s the high collagen content that the medical world currently finds interesting. Medical specialists in Britain are now wondering if those 18th century court surgeons were onto something, and they’re experimenting with isinglass powders and sponges as a way to quickly heal persistent wounds, sores and ulcers.

Wine yeast4. Dead yeast

Of course you know that yeast is used to ferment grapes into wine, but did you ever stop to think about what happens to it after it’s outlived its usefulness? The primary fermentation takes about a week  and then the yeast dies. It sinks to the bottom and forms a sticky tan mess called the ‘lees’.

Although wines are then ‘racked’ (drained off) the lees, there may still be some lee sediment in the wine In fact, if a winemaker feels that a wine (white wines like chardonnay particularly) could use a little more pastry character, the lees will be saved in buckets, poured back into the wine, vigorously stirred around, and allowed to settle again. Yum, this wine tastes like apricots, baked pears and … pastry.

5. Brettanomyces

Brettanomyces is a spoilage yeast that loves to set up housekeeping in wooden barrels and tanks. Brett gives wine a variety of off flavors, ranging from stinky tennis shoes to metallic flavors. Once a barrel is infected, it is almost impossible to remove the yeast, and so winemakers are very careful when moving wines from barrel to barrel to check for Bretty barrels which might infect the rest. When a Bretty barrel is discovered, the wine is usually discarded. Since the value of a barrel of wine could be around $4,000 winemakers are not happy to find a Brett infection in their cellar.

Brettanomyces is not dangerous, and small amounts of this yeast may give wine a complex aroma, but it’s not to everyone’s taste.

6. Sulfur dioxide

Although wine bottles are required to claim “Contains Sulfites” on the label, most winemakers use as little sulfur dioxide as possible, and most wines have no more than 50 parts per million of free sulfur dioxide. However, occasionally a winemaker has to deal with grape, wine or barrel infections that may require a more liberal sprinkling of sulfur. It’s like cooking with salt—a tiny bit improves the overall flavors of a dish, but overabundant use can ruin the whole thing. A wine with high levels of sulfur dioxide will smell like burning match heads, and may elicit a sneeze.

There is no such thing as a sulfite-free wine, just as there is no such thing as a sulfite-free egg. All wines contain some level of sulfite, because sulfur exists naturally in grapes, particularly on the waxy skins which attract dust and elemental minerals from the vineyard in which they are grown. This is why organic wines that do not add sulfur during the winemaking process may only label their wines as ‘No Added Sulfites’.

7. Hydrogen sulfide

If you encounter a bottle of wine that smells like rotten eggs when first opened, this is due to hydrogen sulfide, a gaseous problem sometimes encountered during fermentation. Think of it as a wine fart. It seldom survives the scrutiny of a careful winemaker, but it does occasionally make it into the bottle. The human nose is extremely sensitive to hydrogen sulfide and can detect it in minute quantities. The H2S aromas may resemble rotten eggs, cabbage, skunks, garlic or burnt rubber.

If you encounter a wine with this symptom, don’t discard it right away. Let it breathe for half an hour or so—the unpleasant aroma might blow off, and you may end up enjoying the wine after all.

8. Diammonium phosphate

Diammonium phosphate, or DAP, as it’s referred to by winemakers, is used as a yeast nutrient to help prevent the aforementioned rotten egg wine farts. It is also used to support cheese cultures.

DAP is made of phosphate rock, sulfur and ammonia, all cooked together into a hot slurry, which when cooled, becomes one of the most widely used phosphate fertilizers in the world.

DAP gives the yeasties the trace minerals they need to overcome weak fermentations or extreme temperatures. However, DAP is added in very small quantities, and once the yeast have eaten their share of DAP, there should be none left in the wine.

9. Copper sulfate

Copper sulfate is used to ‘brighten’ up tanks of wine that have gone flat and lost their fruity character. In the U.S. winemakers can add no more than 0.05% to wine. Copper is a common mineral in food and necessary for healthy nutrition and metabolism. However, elevated levels of copper can cause heart palpitations, difficulty breathing, and hallucinations.

Some wineries pour liquid copper sulfate into the wine. Boutique and old school producers may splash the wine over a copper grate or stir it with a copper rod. Copper sulfate can also be used to clear up wine farts (hydrogen sulfide). It works by ‘letting go’ of its sulfate partner and binding with a sulfide instead (think of it as a new trophy bride). The couple then sinks to the bottom of the tank or barrel as a tarry residue and the cleaned up wine is ready for racking.

10. 2,4,6-Trichloroanisole

Every once in a while, a devoted wine consumer will encounter a corked bottle. It might be expensive or cheap, French or local. But what nearly all corked bottles have in common is a cork. Mold and moisture occasionally set up housekeeping in a cork, despite sanitizing efforts. The chlorine used by cork producers to sanitize the corks is, in addition, thought to contribute to the factors which create a skanky smelling condition called 2,4,6-Trichloroanisole (pronounced “corked”).

If you encounter a corked wine, you will have no doubt. It will smell like a hot, musty attic with dead mice in the walls. Some oenophiles also complain that it smells like an old grill or aluminum foil. Ask your waitperson to take the bottle back and bring another (at no charge to you, of course).

Hopefully, your wine tasting experiences will include only the typically touted aromas and flavors, pleasant things like orange blossom, pear, and pineapple in white wines– and black cherry, plum, cassis and cinnamon in red wines. But if you taste a wine that you really don’t like, be prepared to craft your own opinion. Perhaps something like, “I’m sorry, but this wine has off aromas of old paper and mouse fur, with flavors of balsamic vinegar and Meyer lemon, followed by a lengthy aluminum foil finish.”