Aromatics: An evolutionary perspective

Welcome again to Terroir Tuesday.   I hope all haven’t been waiting too long to learn more about really cool stuff.  Tonights essay summarizes a recent talk given at the WAWGG Conference in Richland, WA by Assistant Professor Gavin Sacks of Cornell Univeristy entitled “Riesling Aroma Precursors.”

I hope you’ve selected at least a three to four year-old riesling to accompany you in tonight’s reading.  A gewurztraminer, gruner veltliner, or a siegerrebe would also be good choices.    Maybe some risotto to help wash it down.  Yum.  I don’t intend tonight’s read to be too complex, but rather full of intrigue, elucidating facts, and brilliant inspiration to carry you into tomorrow.  Wednesday. 

Ok, I start with a question:

Q: Why do grapes and wine have aroma?

A: To coax their seed dispersal assistants to eat them of course.

Nice.  Good answer.  So next question,

Q: Just who are these seed dispersal assistants?

A:  Hmmm…not sure.  Why don’t you tell me?  You’re the one writing this stupid essay.

Q: Alright, if that’s the way its got to be.  For anyone who has ever planted a vineyard, and then attempted to harvest grapes from said vineyard, you may have noticed that the birds ate the grapes.  Many of them.  Maybe all of them.  This is why grapes have aroma compounds.  To attract birds to eat the grapes, and then poop the seeds somewhere else.  This is why grape seeds are small, grapes are perfumed, but not overpowering, and they are often red.  Fruit that is designed for birds have small seeds, thin skins, go through dramatic color change as they approach ripeness, and produce sugar.

Fruit that is designed for mammals on the other hand is quite different.  The fruit is bigger and fleshier.  This is why passionfruit, guavas, avocados, durians, and other savory, fleshy, big pitted fruits are designed.  Birds like dainty scents, mammals like stinky scents.

If you learn anything about wine aromatics tonight, learn this.  A grape has many aromatic compounds, but a vast number more are stored inside the vacuoles of the grape and are termed “aromatic precursor molecules.”  They are often chemically bonded to either a sugar molecule, or a sulfur-containing amino acid.

In that form, they do not add aroma or flavor to the grape or juice.  Through the process of primary fermentation, the eating of sugar by yeast, and further through the process of wine aging, these precursor molecules, attached to either sugar or amino acids, are unlocked and the aroma compound travels up the glass, and into your nose.

Huh?  Really?  Does that mean…it can’t be…Yes, go ahead.  Ask it.

Q: Why do grapes have “aroma precursor” molecules since birds don’t make wine?

A: God wants us to enjoy wine.  (Gasps, shrill horror sounds)

Q: Are you about to get religious on us?

A: No.  I’m just saying that it’s wierd that grapes have aroma compounds that are only unlocked through the winemaking process.  Here’s a little more.  Gavin and his research team looked at the aroma precursor molecules in Riesling, in particular monoterpenes and the infamous, TDN.  I won’t bother to tell you what TDN stands for, but it smells like kerosene or diesel, and it is almost exclusively found in aged rieslings, more often Alsatian or German ones than in New World wines.

Here’s some crazy stuff they found out.  They did a petiolar (leaf stem) analysis, and found that when the vine was damaged by plucking a leaf off or cutting the shoot off at the tip, the sap that flowed to the scars contained higher levels of terpene (the beautiful floral scents).  In other members of the plant world, these chemicals are in fact toxic to some animals, and are used to protect the plant from being eaten, or infected by disease.   As the wound heals, the vine now has these toxic chemicals to dispose of.  To protect itself from their toxicity, it attaches a sugar or an amino acid to them, and stores them in the grape.

Q: Hmmm…does that mean muscat is poisonous?

A: No.  It just smells really good.  We are ingesting teensy amounts of these aroma compounds.

Q:Cool.  Is that it?

A: Almost.  TDN is not in the terpene family, but in a family of chemicals called the norisoprenoids.  I love that word.  Say it again with me, norisoprenoid.  The TDN precursor comes from a molecule that is involved in photosynthesis.  Gavin’s team found that if they pull leaves right before veraison, (in July when the berries are changing color), the wines will have maximum values of TDN.  The hypothesis is this,  in response to the increased sunlight on the vine and the loss of leaves, the vine compensates by making more photosynthesis (turning sunlight into sugar) molecules to deal with the damaging effects of the sun.

As the vine and the fruit mature into harvest, those extra molecules are then stored in the vacuoles (storage units of a cell) of the grapes.  When we make wine, yeast unlocks the sugar bond, aging continues to unlock them, and voila, a delicate balance of rubber, diesel, apples, and roses.  Here’s a toast to riesling producers, from Washington State, to New York, from Colmar,  to Geisenheim.

Okay, let’s end on something really cool.  Vitis labrusca, the grapevine that gives us such wine as Manischewitz and other Concord wines, contains a chemical called methyl anthranilate.  Sounds really good, huh? It’s not.  It’s what gives concord wine that unmistakeable flavor of…weasel urine.  You think I just made that up huh?  It turns out one of the only other places in nature that this chemical is found is in the scent ducts of weasels.

Q: Wierd.  Why would I want to drink weasel urine?

A: Exactly.  You and the birds that might steal the concord grapes will be thoroughly displeased.  Explanation: The grape makes this chemical to let the birds know that a weasel is awaiting in the canopy ready to pounce.  Concord grapes tend to be fleshier, have bigger seeds, and yes, are naturally dispersed by mammals.

Cheers

Michael Penn

Mike’s Microbiology: Understanding Wine Aromatics and Flavor

Mike has provided a hugely informative essay on the makeup of wine.

The following essay is the 9th installment in a series of essays entitled “The Top Ten Things I’ve Learned About Wine in the Past Year.”  The idea was to start writing, and maybe someday, write a book. Instead, we’ve started a blog. That dreaded word, more time of your life wasted in front of a blinking screen. Well, this one involves myself, some classmates, and our adventures in wine.

Q: What is wine made out of and why does it taste like it does?

A:  Good question.  I’ll start off the response in simpler terms, and as we go on, I’ll amp it up a bit.

Wine is made out of grapes and the yeast, bacteria, mold, and insects that live on them.

Wine is mostly water.  It got there in several ways.  The grapevine roots absorbed water throughout the growing season, and about 1% of the water that the vine used made it into the grape.  Next, the winemaker added water so that the wine won’t become too alcoholic, he diluted it. We call this post-harvest irrigation.  With that aside, It is often nice when drinking wine to perceive a minerality taste.

Q: What the hell is minerality?

A:  I’m not sure.  I’ve found myself more and more observing the taste of mineral water and sparkling mineral water to see if I can tell a difference.  Check it out.  Calcium, magnesium, potassium, sodium, zinc, copper, chloride, lead, cobalt, manganese, silver, they’re in there.  Doing stuff.  Wines that are described, as the french say, “mineralite, ” often come from old vines, deep soils, and from grapes with subdued “fruit”  complexion.

So, there is water.  What else?  How about acidity.  There are three major acids in wine, and three minors.  Let’s talk the major acids.  The most important is tartaric.  Tartaric is one of the most durable acids in the botanical world.  There are bacteria that can live off of and actually consume many of the acids found in common fruits (apples, cherries, lemons…) Wine is unique.  Hard Apple Cider, Hard Lemonade, Hard Any Fruit, can only survive as a drinkable intoxicant until the indigenous bacteria consume the acids involved.  This is the main reason why wine can survive for more than a hundred years.  Thank you tartaric acid. (There is a rare species of Lactobacillus that can consume tartaric acid.  This rare phenomenon is called “La Tourne.”  I have yet to experience this.)

Q: What does tartaric acid taste like?
A: Sour Patch Kids.  Look at the ingredients.  It’s in there.  It makes your mouth pucker, drool, and then you feel like eating something.

Enter malic acid.  Malus, the latin word for apple.  Malic acid is the sharp and crisp acid of biting into a granny-smith apple.  This acid is in thick supply in apples, crisp Sauvignon Blancs from Loire, France or Marlborough, NZ,, or snappy Pinot Grigio from the Tre Venezie (northeastern Italy).  In the grape, this acid is in high concentration in August.  As the grape begins to shut down in September-October, this acid can actually be consumed by the vine to create ATP(energy).  This is why hotter climates have less acidic wine and cooler climates have more acidic wine.  All because of malic.

Thirdly, there’s lactic acid. Think Lactose – Milk.  This is the acid in milk, and in our bodies after working out too hard.  It is a by-product of bacteria eating the malic acid.  In warmer climates (Spain, California, Southern France) a bacteria eats malic acid and creates lactic.  When a Chardonnay is more creamy, buttery, nutty. Oenococcus, a very small bacteria, has more transformed the malic acid into lactic acid.

Q:  Water, acid, anything else?
A:  Good question.  Yes.  Sugar.  Glucose and Fructose are made by the leaves in the ever-popular “photosynthesis.” These two sugars are put together in the leaf cells and shipped to the grape berry in the form of sucrose, “cane sugar.”  Yeast eat glucose easier than fructose.  A wine with “residual sugar” has sugar that was not consumed by the yeast and turned into alcohol.  A wine that is “Dry”, has no remaining sugar, it has all been turned into alcohol.  A “sweet” wine is a wine where the yeast get too stressed, go on strike, and stop making alcohol leaving behind uneaten sugar.  This is what makes Sauternes from France, Trockenbeerenauslesen from Germany, Lush Zinfandels, Stickies from Austalia, and any other sweet wine, sweet.  Unionized yeast. Alternatively, brandy can lead the way.  Another way of making a sweet wine is to kill the yeast with booze.  This is how one makes a Port.  Stop the fermentation by adding distilled, hard, booze.

Q: This sounds interesting, I’ve heard of this so called, “alcohol.”
A: Ethanol, Grandpa’s ol’ Cough Medicine, C2H5OH.  Whatever you call it, it has been helping you get laid for years.  Yeast make ethanol when they eat sugar in the absence of oxygen.  Wine tends to be anywhere from 11 to 16 percent alcohol.  Eventually, the yeast die because they made too much alcohol (their cell membranes get stretched out like an accordian, poor fool).  As you may or may not know, pure ethanol can almost taste sweet, hot, or viscous.

Q:  Wow, anything else?
A: Tannin.  Tannins are complex ring shaped molecules (phenolic compounds), sometimes occuring in chains (polyhphenolic compounds), and are what makes tea and wine taste, bitter.  They are found in the skins and seed.  As they pass over your tongue, the draw out your salivary proteins.  This makes your mouth feel like you are “chewing on a rug.”    Good?  Yes.  Tannins are a diverse family of molecules, of which nature and plants are abundant in.  They make wine “complex,” and tannins help break down the fats in rich steaks (this is why syrah goes with a New York Steak so nicely).

Among the tannin family is a chemical called resveratrol, one of the best chemicals from “nature” that helps our cholesterol stay low.  Another branch of the “tannin” family tree includes anthocyanins.  These are the color pigments of cranberries, raspberries, blueberries, pomegranates, grapes, etc.  They act as antioxidants when we consume them, scavenging crazy radicals.

Q: Is this essay supposed to be boring?

A:  Hmmm…I was starting to get excited, I was talking about radicals.  Want to hear about aromatic compounds?  Alright, I thought you would.  Let’s get this party started.

As grapes ripen, first they are very acidic.  From July-September, the sugars are rising.  Also, amino acids, vitamin B and C, and potassium salts are being formed,   Finally, October. The skies start to grey and the temperature starts to drop.  This is when the winegrower and all the people who enjoy wine start to pray.  The last thing to develop in a grape is the aromatic compounds.  These are unique, and what makes a grape taste like the Earth has stood still, and a bright light from above is shining down good will to mankind.  Aromatic compounds tend to exist in the space between the flesh and the skin of the berry.  Their average weight is about 702 nanograms.  They are delicate, they go away with too much heat and sun, and they are what make wine taste like the earth is new again.  They are what give a wine “varietal character.”

Here’s the game, you drop a flavor, I tell you the chemical and where it came from.  Caught your attention?

Q: Aight.  Bell pepper.
A:  2-Methoxy-3-isobutylpyrazine.  This compound is found in Merlot, Cabernet Sauv and Franc, Carmenere, Sauv Blanc.  It is made in the photosynthesis process and is transported to the grapes.  This flavor can be reduced by picking late.  It is deteriorated by sunlight.  These varieties are genetically dispositioned to make this flavor.

Q: Not bad.  How  about flowers, like in a muscat for example.
A:  The abundance of floral compounds in a pretty white wine numbers from about 10-20 compounds.  First, linalool(lin-a-lo-o-o-o-o-ol).  This chemical is common in many flowers such as basil, lavender, coriander, and hops.  Widely found in varieties like Riesling, Muscat, and Gewurtztraminer.  It is a delicate chemical, and these wines need to be treated accordingly.  These grape varieties have a genetic predispostion to make this compound in the cells of the leaves and place this delicate, floral, aromatic, unique, chemical into the berries as they approach their ideal ripeness.  Its sensory threshold is about 7.2 parts per billion, or 7 micrograms per liter of wine.

Let’s talk more about these floral chemicals sent from heaven.  A couple more at you, Beta-damascenone, geraniol, Cis-rose oxide, beta-ionone.  A vial of these would trigger your memory to think of roses, violets,or geraniums,  The same chemicals in these flowers are made by the grape berry cells as they approach their ideal ripeness.  Could creation be any more beautiful?

Q:  Alright.  How about coconut.
A: Cis and trans lactones.  These are chemicals leached by oak barrels into the wine.  Its a chemical found in oak wood and it smells like coconut.  American oak contains more cis than trans.  What does that mean?  A more pronounced coconut in American oak than French oak.

Q:Shit. Are you serious? What’s going on here.  Are you about to get jiggy?
A: Yes.  I am.  I could list about 100 compounds that are found in oak barrels, grapes, grape stems, compounds made by yeast, made by bacteria, made by mold.  Such compounds create aromas like litchi, grapefruit, cat pee, honey, black pepper, cotton candy, white pepper, black currant, apricot, ginger bread, cloves, bananas, cigar box, blackberries, fresh-bread and more.  Each one of those is an ester, or a monoterpene, or some other electrochemical-magnetic resonance sent from heaven to make life worth living.

Let me break it down.  Ethanol is the playing field, and these various chemicals are the players.  Some players are synergistic, and some are masking. Some aromas are made by spoilage organism and make wine smell like shit, or barnyard, or bandaids, or vinegar.  I’m not going to talk about those anymore tonight, they make me feel like rotting fruit.  Others are from the oak, some from the grape, some from the yeast, some from the Lactic acid bacteria, others can be from eucalyptus trees on the property, or even stones in the soil.

If I were to place a vial of Ethyl 2-methyl butyrate in your face, you’d tell me it smelled like chemically treated strawberries, like at the dentist’s office.

Q: Wierd, sounds like science, or New Jersey.  Aight, so If that same vial had some cysteinil-related mercaptans, what would it smell like?
A: Great question.  Fresh strawberries.

Q: Really?  Like straight from the farm?
A: Yeah.  This is an example of a synergistic aroma relationship.  The grape made a compound that made the other compound smell better, so that the birds want it more, so that they spread the seeds.

Q: Shit.  Alright.  Go on, tell me some more crazy stuff..
Oak:
Guiacol and 4-Methyl Guaicol– smoky, charred, toasty aromas.  Made when the oak staves are toasted in the fire
furfural and 5-methyl furfural– sweet, butterscotch, caramel, almond.  Made when cellulose and hemi-cellulose are combusted during the toasting
Eugenol and Iso-eugenol– Cloves.  Increases as a white-rot fungi “seasons” the oak staves over a process of 2-3 years.
Bacteria:
Diacetyl–  Butter.  Bacteria that eat the malic acid create this chemical, and then reabsorb it.  Think California chardonnay.  Thank you Oenococcus oeni.
Yeast: Isoamyl Acetate– Banana/Fruity.  Yeasts make chemicals that become esters in the presence of alcohol.  The majority of young wines smell fruity because of the yeasty esters.  As wines age, the grape esters are unlocked.

There are a lot of different compounds found in different wines, and this is why wine is so beautiful.  This is the palette that the winemaker paints his canvas.  Life likes to make life better, biophilia.  In young wines, many of the compounds are ready to be smelled in the ester form.  Meanwhile, a lot of the aromas are locked away, tied to a sugar, or known as a glycosicidic precursor.  As the wine ages, these vine created chemicals become available to the nose.

You’ve been reading for a while now, and I don’t want you to feel overwhelmed, plus I need to go to sleep and bottle wine in the morning.  Wine is meant to be enjoyed, and the main point of this essay is that wine tastes like the Earth that it comes from.  Forest floor, roses, passion, and love itself.  With enough popular demand, I could compile a complete list of aromatic compounds. Until then, our blog is about to get lit up.  Stay tuned for the top 10 microbes of 2010.

Michael Penn

Footnote: Much of this information is sourced from a presentation available here.