The Science And Tradition Of Winemaking

DolomitesSince my last name means “grapes” in Italian, it is fitting that my father and brother are both amateur winemakers. While my dad stubbornly sticks to medieval techniques, my brother, a chemical engineer, makes use of science. But although our understanding of winemaking has deepened, and although additives serve an important purpose, the basic process has remained unchanged for about 6000 years.

Commercial winemakers who rely on grape suppliers and hobbyists are both at the mercy of the harvester, who exercises control over the most critical stage of winemaking. The concentration of various grape ingredients that will impact the taste of wine vary significantly. During ripening, the levels of sugar, phenolic compounds and aromas rise while the amount of acid decreases. A few weeks before picking grapes, results of laboratory analyses and weather forecasts are consulted to choose the optimal time for harvesting.

Lugs of Cabernet Sauvignon and Cabernet Franc. The latter is added to shorten the time it takes for the wine to mature.

No winemaker in my extended family relies on concentrated grape juice from kits. Instead they get their fruit from 36 pound wooden cases called lugs. These make their way to Montreal from California by either truck or train. Upon close inspection, a few bunches don’t exactly appear to be fresh off the vines. But most are impeccable and delicious, far sweeter than table grapes. As a kid I would often sneak into the garage to smell and taste them.

The two main sugars in grapes are fructose and glucose, accounting for a whopping 18 to 25 % of their content. Pectin only accounts for about 0.06%, which is why it’s necessary to add pectin when making grape jam. But in winemaking that same amount of pectin has to break down; otherwise it reduces the clarity of wine. In dry wines, most of the sugar will have been converted to alcohol during fermentation, an oxygen-independent reaction that provides yeast with adenosine triphosphate (ATP).

Why is the acid-level important in winemaking? Low acidity (high pH), common in grapes that are too sweet because they were grown in excessively warm climates, lowers the amount of subtle flavors in the grapes and wine. There is also an optimum pH for fermentation because, as Pasteur demonstrated, it is an enzyme-driven process. Prior to fermentation, pH is measured either by titration or more conveniently with a pH meter, and if it is too high, an acid blend is added. The acid blend consists of the three organic acids that are found in grapes: citric, malic and tartaric, the latter is less common in fruits but the most common in grapes. It led to Pasteur’s
discovery of enantiomers, molecules that are mirror images of one another. (The original Pasteur experiment, however, has been difficult to replicate.) Yeasts themselves will then add a small amount of other acids to wine.

 (Cork of 15 year old wine showing tartaric acid crystals. A wasp investigates.)

Homemade fermentation tanks. A separate tank is used for each grape variety.

Phenolic compounds which include the same type of compounds that make autumn leaves red affect the astringency and color of wine. Normally fermentation occurs in stainless steel tanks. But some chardonnay wines undergo fermentation in oak barrels and owe part of their taste to tannins transferred from the wood.

When grapes have the right balance of sugar and acid, they are harvested and are quickly brought to the winery to be destemmed and crushed. Destemming the grapes prevents the stalks and stems from being crushed with the grapes, which would produce an excess of tannins. Red grape juice or must is fermented with their skins to extract color. White grapes are pressed after they are crushed so only the juice is kept for fermentation. A five to ten percent solution of sodium metabisulfite (Na2S2O5 also added to preserve epinephrine in epipens) is added to kill wild yeast on the grapes. This creates an equilibrium with sulfur dioxide(SO2), the truly active ingredient. The wild yeasts are too varied in composition and are often intolerant to wine alcohol concentrations, causing fermentation to stop prematurely, leaving a high residual sugar content in the finished product. In addition, SO2, inhibits enzymes that oxidize phenolic compounds responsible for discoloring wine. If a minimum of 80 ppm of SO2 is not present, more SOgas is bubbled into the juice, but the legal limit is 200 ppm.

Due to SO2 treatment, fermentation won’t start until a selected wine yeast is reintroduced, usually a pure culture of Saccharomyces cerevisiae. Interestingly my father and brother have at times started with the same grapes, with my dad refusing to add metabisulfite and yeast to his vat. You can guess which wine usually comes out looking and tasting better.

Fermentation is an exothermic process (it releases heat). But in winemaking, the temperature cannot exceed 29oC for red wines or 18oC for white wines), otherwise the growth of yeast cells may stop. Moreover, a lower temperature is desirable because it prevents the loss of volatile aromas and flavours. In homemade wine, excess heat is usually not a problem, but since large commercial vats have lower surface to volume ratios, they cool to slowly on their own.

As sugars get converted to alcohol, the density of the mixture decreases. Since an aqueous alcohol is less dense than an aqueous sugar solution, a hydrometer can help determine when fermentation has stopped, usually when the specific gravity has fallen to about 1.000. An alternative to measuring sugar concentration is the Fehling reagent. I’ve also watched my brother use a hydrometer prior to fermentation to predict the wine’s potential alcohol content.

The freely run juice after fermentation is of the best quality. Going for quantity by squeezing the pulp dry severely compromises the quality of wine. It should be used only for later distillation of alcohol, which can then be added to other products. My father is fully aware of this fact, but driving his cost down to two dollars per bottle unfortunately takes priority over fine taste.

To clarify the wine, the fermented juice is transferred into a settling vat, or if made on a smaller scale, into a demijohn. In these, suspended yeast cells, cream of tartar and particles of skin and pulp settle to the bottom of the container. As the yeast cells break down within the precipitate, they stimulate the growth of Lactobacillus bacteria that convert the wine’s malic acid into lactic acid. This malolactic fermentation process is especially important in wines made from highly acidic grapes because lactic acid is a weaker acid than malic acid. (Bacteria decarboxylate malic acid , thus removing one of the acidic carboxyl groups), so it mellows the wine’s taste.

After the demijohn stage, the wine is repeatedly racked to leave behind less and less sediment called lees. During the repeated racking, the wine is also given a chance to rid itself of the excess carbon dioxide from fermentation. As the CO2 escapes, oxygen enters the wine with each transfer, helping eventually to age the wine.

The wine’s final flavor comes from its blend of phenolics, acids and sugars. But aromatic compounds are said to give it “character”. In reality we do not taste wine without also smelling it, and molecular gastronomists remind us that we don’t perceive what we smell directly through the nose in the same way as what we smell through the mouth. The concentrations of volatiles is quite low: in the 1 to 4 ppm range. The fruity or floral smells are due to the monoterpenes (natural products with repeating units of carbon and hydrogen but ending with an OH group) containing citronell, alpha-terpineol, geraniol and linalool. Aged wines have compounds like vitispirane and TDN(1,1,6-trimethyl-1,2-dihydro naphtalene).

In the CBC documentary by Josh Freed, “The Trouble With Experts“, a professional winemaker and university professor fooled wine-tasting experts by switching the labels on them. Non-connoisseurs, however, preferred the more expensive wines, without knowing which was which. The idea was that expectation plays a role in judgment, but there is a distinguishing chemistry between different wines, nevertheless, one that is not always worth the exuberant price difference.

Occasionally, despite my dad’s outdated winemaking methods, I have caught myself saying, “You know, this wine isn’t half-bad!” Especially after the first glass.

Edited by Ted R. Uva

Originally published Oct 1, 2011; updated Oct 3, 2014

Other Sources:

Amerine, Maynard. Wine. Scientific American.  August 1964.

United States Department of Agriculture

Learning About Marijuana From Washington University

640px-Hemp_plants-cannabis_sativa-single_3Whether or not a drug is legal, simplistic slogans, scare tactics and moralizing never help people make responsible choices. Education is the best tool we have, and Washington University has put together the most readable and up to date marijuana web site I have seen.

While being fairly comprehensive, they do not pretend to have all the definitive answers. I will highlight those areas along with more clear-cut ones that were nebulous in my mind thanks to rumors, self-biases and our media’s tendency to put truth through a juicer. In certain cases, I will also provide more detail.

Effects on Memory

Some marijuana users get lost in their thoughts, forget what they are doing, and let immediate objectives slip away. It’s one of the drug’s attractions, allowing people to temporarily escape from drudgery or problems. This in part is due to weed’s effects on short term memory. Hippocampus_smallThere are receptors (proteins) which interact with marijuana compounds known as cannabinoids. One receptor- type, CB1, is concentrated in the sea-horse shaped hippocampus, a brain structure involved in memory formation. Long-term impairments may also be possible, but more investigations are needed to see if that concern is real.

More on Cannabinoids

(−)-trans-Δ9-tetrahydrocannabinol (C21H30O2). Like all cannabinoids, THC has 21 carbon atoms and a C5H11 tail bonded to a phenolic group.

There are close to 100 known cannabinoids,
most of which are not psychoactive. Those that do not act on CB1 receptors but on CB2 receptors are found in the immune system and spleen. The main mind-altering compound acting on CB1 receptors is  (−)-trans9-tetrahydrocannabinol or THC. A single serving in a marijuana edible contains 10 mg of THC. In smokable forms of the drug, the THC concentration of dried leaves, flowering tops and hashish oil ranges from 1 to 20%. Since a joint’s mass is between 0.25 to 1 gram, it translates into a range of 2.5 mg to 200 mg of THC. This is two to seven times stronger than weed from the 1970s, not a factor of 30, as reported in the media.

345px-Cannabidiol.svgCannabidiol (CBD) and its related isomers can make up almost 40% of cannabis resin, and so are the most common group of canniabinoids found in hemp. Although not directly psychoactive, it has other positive effects sought after by medical researchers and patients.  Until recently, American marijuana was unfortunately low in cannabidiol, which has a low affinity for both types of receptors but controls the way other cannabinoids interact in the brain and elsewhere in the body. For instance, it may decrease three side effects of THC: anxiety, sleepiness and dependency. This is an example of what researchers Machoulam and Ben-Shabat call the entourage effect. Many marijuana compounds, in individual purified form from the lab, do not act on the human body like they do in a group, as when the plant is smoked or eaten. According to a review of the literature in the British Journal of Pharmacology evidence supports the entourage effect, which is important in medicinal chemistry:

Considered ensemble, the preceding body of information supports the concept that selective breeding of cannabis chemotypes rich in ameliorative phytocannabinoid and terpenoid content offer complementary pharmacological activities that may strengthen and broaden clinical applications and improve the therapeutic index of cannabis extracts containing THC, or other base phytocannabinoids.

Smoking and Driving

A safety margin of 3 to 4 hours is needed to drive after smoking pot and at least 5 to 6 hours if brownies are eaten because the effects of the latter only kick in a couple of hours after ingestion. Under the influence, reflexes can slow down and some “buzzed” drivers do not stay on their lane with optimal ability. Alcohol will accentuate these effects.

Teenage Use

Use by adolescents presents higher risks because the brain is in a rapid growth stage, and such early use is more likely to lead to dependence. Cannabis’ short term effects on memory can impact success in school, and if marijuana has any long term effects, a jump start in usage will increase the probability that such effects will materialize. These reasons motivated the setting of the legal age for consumption and purchase of marijuana in Washington state and Colorado at 21, the same for alcohol elsewhere in the country.

Other People Who Place Themselves At Higher RiskPregnant-woman-no-to-smoke1

Schizophrenics or people genetically predisposed to the condition are at a higher risk of a psychotic episode while under the influence of cannabis, which is a very rare side effect.

THC crosses the placental barrier, and although its effects on the fetus are unknown, pregnant women are advised by doctors to stay clear of it and treat it like tobacco, alcohol or any other psychoactive drug.

Effects on Lungs

Marijuana smoke is less harmful than tobacco. The former does not obstruct airways or cause emphysema. But it’s not entirely innocuous. The connection to pulmonary infections is not clearly established. And there is more tar deposited in the lungs per joint than per tobacco cigarette, so the link to cancer cannot be easily written off. None of the investigations are conclusive so far, and of course any risk will be in proportion to the quantity smoked.

Obscure Molecules In Familiar Smells

At both the macroscopic and micro levels, not all organisms get equal attention. Because of their sheer numbers, there are still undiscovered species of plants and roundworms at the feet of botanists and zoologists, respectively. Other specimens have been named but little is known about them. At the astronomical level we come across two factors: an overwhelming number of stars and bodies, compounded by a detection limit.

The latter is rarely a problem for molecules, but there are so many combinations of atoms possible, especially when both their sequence and arrangement in three dimensional space has such a marked effect on chemical properties. Just the single association of carbon, hydrogen and oxygen in a ratio of 6:12:1hexanal (C6H12O) has produced almost 300 versions(isomers), and only one, hexanal, gives off the scent of freshly cut grass. Here are fairly well-studied molecules of the same three elements but in different ratios. Not having found their way into too many scientific magazines or websites, they are obscure molecules in familiar smells that should be part of the popular imagination.

1. Geosmin and its Unsaturated Version

Fertile soil is actually a blend of living and nonliving material, so it’s not surprising that the characteristic smell of freshly plowed earth is due to a  compound released by bacteria. Almost 50 years ago, a mixture of compounds from a smelly strain of Streptomyces griseoluteus was obtained. Some species of Streptomyces decompose leaves and organic matter in soil and are known to produce antibiotics. The investigators tried to purify the mixture through ether-extraction and by using activated charcoal and chloroform. Although they did not reduce it to a single compound, the mixture retained its earthy odor even after it was diluted by a factor of a billion!

Two years later, after using methylene chloride-extraction and gas chromatography, another group realized that the smell did not come from what was previously believed to be a blend of esters, acids, alcohols, aldehydes and ammonia. It was mainly due  to a molecule which they dubbed geosmin. gesominWhen it’s too concentrated, geosmin smells like manure. But when a concentration of 0.7 micrograms per kilogram (the human nose’s threshold) is not too amplified, the molecule’s interaction with nasal receptors is a pleasant experience for most people. It also gives rise to the smell of soil after rainfall. When some animals are drawn to the odor of geosmin they place their snouts into the ground and help distribute bacterial spores.

More recently, geosmin has also been found to be released by some cyanoba


cteria, and the perfume industry have found geosmin in three species of cacti flowers.  Discovered about 15 years ago, the unsaturated version of geosmin, dehydrogeosmin, has a musty, earthy odor and is found in over 50 members of the cactus family. It’s ironic that desert plants are producing a smell that we associate with damp places.  But the smell plays a role in the pollination of the endangered Mexican species Turbinicarpus pseudomacrochele, which produces dehydrogeosmin in a high concentration along with trace amounts of geosmin.

2.   Filbertones and A Related Ketone
Filbertone is a liquid isolated from hazelnuts. The nut contains almost equal amounts of the two mirror image-versions of the molecule known as enantiomers. Prior to their 1989 discovery,  chemists were already familiar with how enantiomers can have different properties. Limonene, for instance, smells like oranges, while its mirror image has harsh lemon notes which can even be mistaken for turpentine.  Similarly, with filbertone, we are less sensitive to the odor of one enantiomer: it is more buttery and chocolate-like. The other has a stronger and more fatty smell. There are, however, dozens of other compounds that account for the symphony of hazelnut aroma.
Filbertone’s ketone group and part of its methylated skeleton is reminiscent of butanedione, a cheesy-smelling compound partly responsible for the flavor of butter. butanedione
The enantiomer ratio of filbertones is fairly constant and independent of the hazelnut’s geographical area. nocciolaWhat inspired that particular investigation is the fact that hazelnut oil is often used as an adulterant in more expensive olive oil.

After laboriously handpicking over a thousand nuts from their socket-like receptacles and drying them for weeks in the Avellino sun, I once tried to smuggle them through the Montreal airport. They were confiscated. I hope the custom officers at least cracked their shells, bit into the kernels and released their filbertones.

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