Food Source Information Wine

Wine is an alcoholic beverage produced by yeast fermentation of fruit juices, along with further processing. Grapes are the most commonly used fruit for producing wine, although others such as apples, berries, cherries, apricots, kiwis, plums, peaches, and strawberries can also be used. Grapevines belong to the Vitaceae family in the Vitis genus; the V. vinifera species is known as the wine grape.

The Vitaceae family is usually characterized by woody, habitually climbing, swollen or jointed nodes, and leaf development on shoots, with flowers or tendrils usually developing opposite of the leaves. The Vitis genus primarily grows best in temperate zones and is only indigenous to the Northern Hemisphere.

Over 10,000 cultivars of the grapevine exist, with each variety having a different appearance and taste. Some of these cultivars were created to improve disease resistance while maintaining the wine-producing characteristics of V. vinifera, and inadvertently improved productivity of the vine as well. While wild grapes require cross-fertilization, domestication of V. vinifera has resulted in cultivars with the ability to self-fertilize.

California supplies over 88% of the nation’s grapes in weight for wine. The state’s wine-type grape acreage is reported as 637,000 acres, with 590,000 of those acres bearing fruit in 2018. Its most popular varieties are Chardonnay and Cabernet Sauvignon.

Italy and France have steadily provided most imported wine to the U.S. since 2015. Australia and New Zealand also supply a significant portion of wine, although imports from Australia have increased the past few years while those from New Zealand have decreased.

Between 2000 and 2020, at least 6 wine-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 40 illnesses, and no hospitalizations nor deaths.

While it did not result in an outbreak, two wineries doing business under Seavin Incorporated voluntarily recalled specific packages of their wine after they learned that they could potentially contain small pieces of glass. This occurred in May of 2018 and no reports of consumer illness or injury have been reported.

Generally, wine is regarded as safe from microbial contamination due to the unsuitable environment (high alcohol content, low pH, high carbon dioxide, low oxygen, and the presence of phenolic compounds known to be antimicrobial) that make bacterial survival and growth nearly impossible. Some studies even suggest that drinking wine with a meal may protect the consumer from foodborne illness. Further, the Food and Drug Administration has classified fruit wines as “low-risk” for causing adverse health outcomes and death.

However, the currently low-risk rating could not be permanent. Fruit juices also used to be considered safe from food poisoning for the same reasons until E. coli O157:H7 and Salmonella outbreaks occurred; now consuming unpasteurized fruit juice is recognized as risky. The ability of bacteria to adapt to harsh environments, as well as the emergence of more virulent pathogens suggests that we may not always be able to assume wine is safe from foodborne pathogens.

In fact, one study done in 2013 (Kim et al.) has already demonstrated the ability of B. cereus spores, E. coli O157:H7, and S. aureus to survive in wine. While E. coli and S. aureus were only able to survive for 24 hours in this study, a different study conducted in 1988 (Sheth et al.) showed those bacteria surviving only 4 hours. This 6-fold difference may suggest the possibility of bacterial adaptation to the wine environment.

Arsenic

Even though arsenic-containing pesticides have been prohibited, arsenic can still be found in the air, water, and other living things in the environment. Grape vines can absorb this arsenic through the soil which is then reduced to its most toxic form by the fermentation process and is detectable in the final product. Chronic exposure to arsenic is known to cause many forms of cancer, including skin, lung, liver, and bladder.

However, after a lawsuit was filed against California wines in 2014 for containing levels of arsenic above the FDA requirements for water, the FDA stated that the water recommendations could not be applied to wine. Therefore, a separate analysis would need to be conducted to determine what levels of arsenic should be considered safe for wine. The lawsuit was dismissed by the courts.

Heavy Metals

An accumulation of excess heavy metal ions can lead to neurological deposits, chronic inflammation, and cancer. To measure the risk of long-term exposure to chemicals like these, the EPA developed target hazard quotients (THQ) which takes the dosage, length and frequency of exposure, and body weight into account. A THQ value at or below 1 is considered safe. One study conducted found levels of Vanadium, Manganese, Copper, Zinc, and Nickel to be above 1 even when the wine was ultra-filtered. These levels were based on a lifetime consumption of 250 mL of red wine each day. Lead and copper were not found to be of concern, which other studies support as well.

Mycotoxins

Grapes are very susceptible to fungal contamination, especially during harvesting time if there is any damage to the skin. The most common fungi for wine grapes are Aspergillus, Botrytis, and Penicillium. Fungi can create mycotoxins that are harmful to humans when consumed.

Aspergillus causes a disease called black rot in the grapes and has been associated with adulteration of wine in the past due to the bacteria’s production of ochratoxin A (OTA); OTA is the most common mycotoxin found in wine and is considered one of the most harmful mycotoxins. OTA is a nephrotoxin that is known to also be carcinogenic, teratogenic, and immunosuppressive. Wine is considered the second most major source of OTA intake. The levels of OTA in wine have a decreasing gradient from red to white.

In addition to OTA, fungi can also produce another type of mycotoxin called fumonisins. Fuminosins are known to be carcinogenic in humans, as well as nephrotoxic and hepatotoxic in rats.

Other mycotoxins have been found and reported in grape products, but they do not have any associated human health effects.

Pesticides

Pesticides, herbicides, and fungicides are used extensively in viticulture to increase vine productivity. While the processes used to create wine dilute the concentrations of these chemicals, their presence should not be ignored.

Chemicals including carbofuran, molinate, boscalid, fenhexamid, cyprodinil, and others have been detected in red or white wines. Pesticides can result in many negative health effects, including cancer, and neurological, gastrointestinal, respiratory, reproductive, and endocrine effects.

Biogenic Amines

The fermentation process may result in the decarboxylation of amino acids and production of biogenic amines. Some biogenic amines come directly from the grapes and some from the metabolic activity of the yeast. When ingested in too high of quantity, these molecules can cause various physiological responses including hypotension, hypertension, heart palpitations, headaches, and allergic responses. Usually red wines have a higher concentration of biogenic amines than white.

Over 9 billion pounds of grapes were processed for winemaking in 2017, with California contributing 8 billion of that. California contributes over 60% of the economic wine shares in the U.S. and accounts for 95% of the nation’s exports.

In 2018, 94 million gallons of wine were imported, of which Italy supplied 33.07% of that volume with France, Australia, and New Zealand supplying lesser volumes. The U.S. exported a total of 16 million gallons of wine, with the majority of it being delivered to the United Kingdom, Canada, Japan, and Hong Kong. The retail value of wine both imported and exported in the U.S. totals more than $69 billion.

Pre-Harvest

Grape vines can be grown in many different soil types if they are provided with adequate anchorage, water, nutrients, and drainage. In fact, vines can thrive in soils that are inhospitable for other plants. Ideally, the pH of the soil should be between 5.5 and 7.0, but vines can grow in pH as low as 5.0 and as high as 8.5. Water, minerals, and nutrients must be applied carefully so that an appropriate balance between vegetative and reproductive (fruit-bearing) growth occurs.

Vines are normally planted in rows and require both training and pruning. Most vineyards today use a physical structure, such as wire, as their training system to provide structure to the vine. Pruning occurs mainly when the vine is dormant, and it helps to control the yield and fruiting.

While flood, furrow, micro-jet, and drip irrigation techniques can and are all used, drip irrigation is the most common.

Pruning can be done mechanically, but often hand work is required after that to tie the vines to the training system and do further cleaning up. This is most commonly done in March when the vines are more flexible. Often during this time, the ploughing between rows is also done. Mechanical pruning is becoming more popular due to its ability to arrange the vine in the best way and increase quality, while decreasing problems with disease.

The tops of vines, shoots, and leaves are often trimmed during the summer to maximize fruit production. Once they begin to ripen, the leaves around the fruit may be removed to allow sunlight to reach the grapes.

A variety of pests pose a threat to vineyards, including insects, mites, worms, animals, and birds. Of all pests, Phylloxera pose the biggest threat as they are completely destructive to a vineyard and move quickly. The only way to prevent their invasion is to use a V. vinifera variety that has been grafted onto an American species rootstock or hybrid, as this species of rootstock is resistant to damage.

Nematodes can eat the roots of vines and cause major problems for growers. It is best to check the land before planting, not to grow after potatoes or carrots, and use nematode-resistant rootstocks to avoid their impact.

Wild animals such as rabbits, deer, and pigs can cause significant damage to a vineyard, even stripping bark and leaves and eating the grapes. Their presence in vineyards poses a threat to consumer safety as demonstrated by one outbreak of tularemia in harvesters after a wood mouse contaminated the mechanical harvester and consequently the must they drank.

Various fungal diseases can impact both the grapes and vine. Most fungi thrive in moist, humid, warm, and shaded conditions. Prevention and treatments for fungal infections include sulfur powder, copper sulfate, Bordeaux mixture, copper, trimming infected parts, and assuring vines and grapes get proper circulation and sunlight.

Vines can also be affected by bacteria and viruses, for which prevention by grafting and disinfecting work tools are key.

Conventional viticulture utilizes machinery, fertilizer, monoculture, pesticides, and herbicides. Monoculture is achieved by ploughing the soil between rows and spraying herbicides. Pesticides and herbicides are applied regularly and frequently—up to 20 times a year.

Wine can also be produced organically and labeled as either “organic wine” or “made with organic grapes” through the U.S. Department of Agriculture. To be labeled as “organic wine,” both the growing of the grapes and processing into wine must be certified. The certification requirements are that all agricultural products used must be certified organic, all non-agricultural products are allowed substances, only non-genetically engineered plants are used, and that sulfites cannot be added to the product. The “made with organic grapes” label has different requirements that include using only certified organic grapes, using only agricultural products that are not on the excluded methods list, and using only non-agricultural products on the allowed substances list. Sulfites can be added to “made with organic grapes” wine.

Harvest

Once ripe, grapes can either be harvested by hand picking or machinery.

In hand picking, the stalk is normally picked with the grape cluster. Pickers normally use small plastic crates to put the picked grapes in and transfer them to the winery. Once off the vine, grapes begin deteriorating quickly, so grapes are normally picked early in the morning and placed into a plastic-line container with carbon dioxide dry ice. They are then chilled as soon as they get to the winery.

Instead of transporting them directly in the small crates, some harvesters dump all the grapes into one large trailer which then transports them to the winery. Wineries focused on quality will then have the grapes go to sorting tables where leaves, snails, or other non-grape materials are removed, but not every winery employs this practice.

The low availability of skilled workers and short timeframe of when the grapes must be harvested has encouraged the development of mechanical harvesting since the 1960s. This method quickly became popular and the amount of wine grapes harvested mechanically increased from 10 to 70 percent in 20 years. Most machines work by shaking the vine until the grapes fall off, which can result in damage to the fruit and leaves it prone to oxidation and microbial attack. To combat these effects, sulfur dioxide may be added to the collection bin to slow the oxidation process until the fruit arrives at the winery.

After they arrive at the winery, the grape stalks are usually removed, and the grapes are lightly crushed. These two processes are usually be done using one machine known as a destemmer-crusher, but they can also be done by two separate machines. After this is complete, the juice and skins remaining are transferred into a fermentation vat or barrel. This mixture is known as the must.

Sulfur dioxide, sucrose, tartaric acid, calcium carbonate, yeast, yeast nutrients, and tannins may be added to the must to prepare it for fermentation.

Fermentation

Once fully prepared, the must is converted to wine through the process of fermentation, or the use of microbial growth and enzymes to convert grape components to the beverage. Fermentation usually produces foods with a reduced risk of bacterial contamination and is viewed as a type of food preservation. For wine, the yeast enzymes convert the sugars into ethyl alcohol and carbon dioxide.

The most commonly utilized microbes for wine fermentation belong to the Saccharomyces genus and they do most sugar conversion. This genus of fungi is not naturally found on grapes and must be added. Common species utilized include S. cerevisiae and S. bayanus. Yeasts that originate in the vineyard are sometimes referred to as “native,” “natural,” “wild,” or “non-Saccharomyces yeasts.” Different yeasts produce different flavors and aromas in the wine, so some wineries will either utilize the natural yeasts, or add specific yeasts with known traits.

This process normally occurs in vats which can be made from concrete lined with glazed tiles, epoxy resin, or cream of tartar. Stainless steel vats have become increasingly popular, as well as wooden vats which are much more difficult to sanitize. Fermentation can also occur in wooden barrels.

Red wines are usually fermented with the grape skins and require mixing to ensure the skins remain in contact with the juice since they normally float to the top. White wines are not fermented with the skins. This mixing can either be done by using a pump which moves juice from the bottom of the vat to the top and sprays it over the skins, or it can be done by hand using wooden paddles to push the layer of skins down.

Final Processing

After fermentation is complete, the juice will be moved from the fermentation vat to another vat, while the skins and grape sediments remain behind. This is called racking. The contents left behind are usually pressed again to obtain more juice.

A critical step of wine production includes the process of blending, where wine from different vats that were harvested and fermented separately are combined to even out any inconsistencies and create the final wine style.

Some wines, usually of higher quality, then undergo an ageing process called maturation. Maturation softens the tannins and reduces harsh flavors. This maturation can take place in stainless steel or concrete vats, or in wooden barrels for 9 to 22 months. Often, the wine going through this process will be transferred several times to other vats to continuously clarify it and remove any sediments.

Before the wine is bottled, it must undergo fining and filtration. Fining involves the use of electrically charged molecules to remove very light particles remaining in the wine that cannot be removed by racking. Most wines are also filtered through a membrane to remove any solid particles remaining. Many filtration methods exist.

Bottling

Although traditionally packaged in a bottle using a cork closure, wine can also be packaged in polyvinyl chloride, aluminum cans, polyethylene terephthalate, bag in a box, screw-on bottle caps, and plastic bottle corks. The traditional packaging method has the longest shelf-life and most benefit to wine flavor for long-term bottle aging.

Western European oak trees are the most commonly used for cork production. Portugal is the largest producer, followed by Spain, France, and Italy. Corks are sterilized by being placed into polyethylene bags which are then filled with sulfur dioxide.

Bottles are sterilized and placed on a conveyer belt where they are flushed with dinitrogen and vacuumed to remove any particles such as dust.

Wine consumption has been increasing since the early 1990s and reached a record high of 2.95 gallons per capita in 2018. This is equivalent to 966 million gallons of wine consumed annually in the U.S. alone. In 2017, wine accounted for 15.23% of the alcohol market, behind beer and spirits, respectively.

People aged 54-72 years old contributed 40% of winery sales in 2018, followed by people aged 38-53 contributing 34%, people aged 22-37 contributing 16%, and people aged 73 and over contributing less than 10%. Males consumed almost three times as much alcohol per capita as females in 2016.

States that have an above average and forecasted increase of wine consumption include Delaware, Idaho, Maine, Massachusetts, Ohio, and South Dakota.

One 5-ounce serving of wine contains approximately 125 calories and 4 grams of carbohydrates. It is not a significant source of vitamins, minerals, or lipids.

Wine, particularly red wine due to its long contact time with the grape skin, contains high amounts of chemical compounds known as polyphenols. These compounds may have antioxidant properties which can protect the body from free radicals that cause cellular, DNA, and protein damage. While the antioxidant properties may not yet be fully established, wine consumption has been found to increase antioxidant levels in the body. These polyphenols also bind to low-density lipoproteins and are thought to decrease the incidence of cardiovascular disease.

A study conducted in 2008 found that even moderate wine consumption convincingly increased the risks of breast, colon, liver, rectum, stomach, and upper aero-digestive tract cancers. The overall risk of cancer was found to increase with high (>5 drinks a day) consumption and was found to have no relationship with moderate (<3 drinks a day) consumption.

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