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New World Wine Maker Blog - Technical Articles

The production of lower alcohol wines

by Charl Theron

During the 1980’s and 1990’s some wine critics propagated dark coloured, full-bodied, heavy red wines. This was exemplified by tannic wines with relatively high alcohol content. The use of phenolic ripeness as criterion for harvesting contributed to this phenomenon. These wines were usually medal winners, but were not necessarily favourites of public consumers. Over the last few years pressure is internationally applied to produce wines with lower alcohol. Traditional Bordeaux and Burgundy wines with alcohol levels between 12.5 to 13.5% have consequently become popular again.

The alcohol content of Californian Napa Cabernet Sauvignon wines increased from an average of 13.2% in 1981 to an average of 15.2% in 2013. A research survey by the Californian wine giant, E&J Gallo, found that persons between 25 to 45 years are interested to experiment with wine and other alcoholic beverages by adding fruit, sparkling water and ice to it in order to develop wine based cocktails.

In 2007 market research by the Californian cellar, Francis Ford Coppola, in the United Kingdom found that 28% of the respondents were concerned about the alcohol content of the wines they buy. The same research found in 2013 that the percentage of concerned respondents increased to 40%. This confirms the international concern about wines with relatively high alcohol content. The most important reasons for the concern are health, social responsibility and the taste of the wine, but countries like the United Kingdom (UK), New Zealand and Scandinavian countries adjusted their tax structures according to the alcohol content of the wines and also restricted the marketing and promotion of high alcohol wines.

The New Zealand government initiated partnerships with 17 wine cellars to research the production of lower alcohol wines without the addition of water or using alcohol reduction technology. The research program will last for 7 years and NZ$ 13 million was budgeted for it. Both viticulture and cellar procedures will be addressed. The challenges in the vineyard will be to produce grapes with lower sugar concentrations, without having natural higher fixed acid concentrations. Sites that naturally produce lower acid grapes must be identified and viticulture practices like lower leaf-grape ratios, irrigation, fertilisation, yield and Botrytis options will be investigated. Water addition prior to alcoholic fermentation or to wine is not permitted in New Zealand and alcohol reduction technology like reverse osmosis and spinning cone are seen as too expensive for low alcohol wines. Cellar practices like the harvest time, pressing, the termination of alcoholic fermentation to ensure balanced wines, yeast selection and temperature control will consequently be investigated. As a result of the cool climate of New Zealand, the production of typical cultivar wines with the necessary balance and an alcohol content of 9% is definitely possible.

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Who’s Your Daddy?: Kerner

The subject of today’s Who’s Your Daddy post is a grape that I’ve never heard of before. As you are probably well aware, there are only really a handful of grape varieties that make up the vast majority of wines that are sold in stores, whereas in reality, there are hundreds of different varieties that have been and currently are made into wines all over the globe.

As a reminder, diversity is important not only for a little variety in your life, but more importantly for the overall health and sustainability of the wine industry as a whole, particularly in this time of climate change. Here is just one example of that diversity:

Without further ado, the focus of this “Who’s Your Daddy?” post is the Kerner grape variety (Vitis vinifera).

Brief History

The origins of Kerner are not too hard to find, considering its creation was relatively well documented compared to many other thousands of wine grapes whose origins are unknown.

Kerner, a white wine grape, was created in the greenhouse in 1929 by August Herold in Lauffen, Württemberg, Germany. The name “Kerner” was assigned to the grape in honor of a German physician and poet named Justinus Kerner. This particular poet was selected due to his works on wine (and if I can ever get my hands on some of this I’ll update this post at that time!).

The plant stayed in the laboratory/greenhouse setting for quite some time, but by 1969 was granted vartietal protection and given approval for commercial production. Finally, in 1993, it was given DOC status by the Italian Demoninazion di Origine Controllata.

Most of the plantings of Kerner are currently all over Germany, with greater concentrations planted in the Pfalz and Rheinhessen regions. The acreage of Kerner is somewhat uncertain; with some sites referencing 8,000 hectares while others referencing only 3,700 hectares. I’m not certain of the date published, but probably the figure I would trust most would be from the Wines of Germany website itself, which states that there are currently about 3,500 hectares of Kerner planted in Germany. In addition to Germany, Kerner is also found in Italy, Austria, Switzerland, England, and Japan …

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Acetaldehyde in wine

by Francois van Jaarsveld and Francois October

Acetaldehyde (ethanal; C2H4O) is a low molecular weight, flavour compound found in a wide variety of aromatic foods and beverages that have, prior to their final stage of production, undergone a degree of fermentation (McCloskey & Mahaney, 1981; Jackowetz et al., 2010). Acetaldehyde has been known to be a product of alcoholic fermentation by yeasts for almost a hundred years, but its presence in wine was not confirmed until 1984 by Dittrich and Barth. It is one of the most important aldehydes (carbonyl compounds) and constitutes more than 90% of the total aldehyde content in wine. Aldehydes, together with a large number of other volatile compounds, are responsible for wine aroma (Liu & Pilone, 2000).

Production

Acetaldehyde is primarily a product of yeast metabolism of sugars during the first stages of alcoholic fermentation. It is the last precursor in yeast fermentation before ethanol is formed, and is produced when pyruvate, the end product of glycolysis, is converted by the enzyme, alcohol dehydrogenase (ADH), to acetaldehyde. Conversely, a secondary source of acetaldehyde production in red wine, which usually occurs after ageing, is oxidation (exposure to air/oxygen) of ethanol, once again facilitated by the enzyme, alcohol dehydrogenase (Jackowetz et al., 2010).

Temperature and acetaldehyde production levels

Controversy still persists regarding the influence of fermentation temperature on acetaldehyde production levels. It was previously reported that acetaldehyde concentration levels, relative to 12, 18 and 24°C, increased significantly at a fermentation temperature of 30°C, which was in direct contrast to reports by Amerine and Ough in 1964 that fermentation temperature does not affect the final aldehyde content. However, it was recently found that cooler fermentation temperatures, in a strictly oxygen-regulated environment, actually led to higher acetaldehyde levels, which could be as a result of a reduced reutilisation of acetaldehyde by the yeasts during the last stages of fermentation (Jackowetz et al., 2010).

Production levels and stage of fermentation

Production levels of acetaldehyde during the early stages of fermentation, differ widely from the final acetaldehyde concentration in wine (Cheraiti et al., 2010) due to reutilisation by the yeast cells (Jackowetz et al., 2010; Li & Mira de Orduña, 2010), as well as degradation by bacteria (Jussier et al., 2006) during the last stages of fermentation …

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2015 Late Season Disease Management

By: Bryan Hed

In many parts of the Eastern United States, 2015 will be remembered as one of the wettest fruit development periods in recent memory. Here at our Penn State research farm in North East PA, rain fell consistently, to the tune of about 2 inches per week, from late May through the middle of July! This level of wetness creates ideal conditions for diseases like downy mildew and black rot, of which there is abundant proof in our unsprayed check plots this year. Even growers of Concord grape, which has limited susceptibility to downy mildew, have been faced with downy mildew pressure they haven’t seen in a long time. Acreage under organic management where synthetic pesticides are prohibited, has, in some cases, suffered heavy losses from black rot. The wet weather also created perfect conditions for the establishment of latent infections of Botrytis during bloom and the early berry development period. These infections lay dormant in clusters until the ripening period (now), when factors related to high humidity, cluster compactness, and berry skin integrity, bring about the activation of these infections and the initiation of bunch rots.

More recently however, we have seen drier conditions prevail (only 2.62” rainfall over the past 7 weeks at our site) that have brought some relief, mainly from downy mildew (the danger of black rot fruit infections was past somewhere around the middle of July). The drier, sunnier conditions are more hostile to the survival of the downy mildew spores and can inactivate much of the sporulation so that an occasional wetting period will probably not amount to much additional leaf infection, at least not in vineyards that have kept this disease under control. Nevertheless, according to DMCast, (the downy mildew infection model developed at Cornell and loaded into the free NEWA website at http://newa.cornell.edu/), occasional wetting events may generate a downy mildew infection period in some locations IF there is active sporulation.  This is why it’s so important to continue scouting leaves for the distinctive white ‘downy’ sporulation of this disease (Figure 1). Growers of susceptible varieties need to keep closely monitoring their vineyards for active sporulation and use that information in combination with the DMCast model on NEWA. If conditions turn wet more consistently, this disease can quickly spiral out of control, strip vines of their leaves and effectively end the season (and the ripening of canes for next year’s crop). So, despite the drier, hotter weather, the solid establishment of this disease across our region in June and July will likely mean that this disease will remain a serious potential threat for the rest of the season! If you find yourself trying to control this disease well into the ripening period, be aware that your list of chemical control options will start to become shorter as we get within 30, then 21, then 14 days of harvest, until in the end you’ll be left with some formulations of captan, copper, and phosphorous acid products.

Figure 1. Late summer downy mildew lesions on a mature leaf of Vitis labrusca ‘Niagara’. Note the absence of the more typical ‘oil spot’ symptoms that are observed on immature leaves in spring. Rather, lesions on mature leaves in mid-late summer take on a blockier appearance but still have the typical white downy sporulation underneath.

Sep_Bryan_Fig 1

The threat of powdery mildew fruit infection (Figure 2) was over weeks ago. But as with downy mildew, leaves are susceptible to powdery mildew all season. However, powdery mildew leaf infection has been building rather slowly from our perspective along Lake Erie, and I see relatively little development of this disease on mature, exporting leaves of Concord and Niagara at our location. In fact the south side of our unsprayed east-west oriented rows are practically mildew free (sunlight is lethal to powdery mildew). Shoot tips, of course, are a different matter; we are seeing the classic distortion of new growth caused by heavy and rapid colonization by powdery mildew. This is nothing unusual, especially for this time of year. After more than 3 months of inoculum buildup in the air, unprotected new growth, which is highly susceptible to infection, is literally thrust into a hornet’s nest of powdery mildew spores and becomes infected as soon as it emerges. In vineyards that have largely controlled this disease to this point, infection of new growth is less severe and less rapid. These infections are also of much less concern (probably of no concern) in juice grape vineyards than in susceptible wine grape vineyards and will have little or no impact on the ripening of juice grape crops in the Lake Erie belt. And, according to work performed by Wayne Wilcox’ program, leaf infections that occur after Labor Day will probably not add to the burden of over-wintering inoculum for primary cycles next year; they likely don’t have time to mature before leaf fall. However, protection of new shoot and leaf tissue may still be important in wine grapes, especially Vitis vinifera. New growth is not only incredibly vulnerable to infection at this time (for the reasons stated above), but collectively serves as the perfect substrate for even more rapid generation of inoculum levels in the air; infected shoot tips represent an important source of late summer inoculum for powdery mildew. Sulfur is often the material of choice for late season control of powdery mildew; it’s relatively inexpensive, it’s effective, and you don’t have to be too concerned about the development of resistance. But too much sulfur on grapes during fermentation can lead to production of hydrogen sulfide which produces off aromas in the wine. When should sulfur applications be terminated before wine grape harvest? Of course, this depends to some extent on rainfall during ripening and sulfur rates. However, recent findings at Cornell (Kwasniewski et al. 2014) have shown that growers of red wines (for fermentation on the skins) should allow at least 5 weeks between that last application of sulfur and harvest (right about end of August for us in the northeast).  With white wines (not fermented on the skins) late sulfur sprays are not thought, generally, to lead to issues with hydrogen sulfide. Other materials that have been used to successfully control this disease on leaves during ripening are things like monopotassium phosphate and formulations of potassium bicarbonates. These materials are not effective on heavy leaf infections but, according to one of my colleagues in Ontario, can work reasonably well if applied often (weekly?) to maintain relatively clean canopies, especially if you’ve exhausted your options of single site synthetic materials (Vivando, Quintec, Torino, Luna, strobies, sterol inhibitors).

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Unique Proteins Identified in Botrytis cinerea-Infected Grapes: Implications for Noble Rot Field Assays

Noble rot, also known as grey mold, is both a bane and a blessing for winemakers. Scientifically known as Botrytis cinerea, it is known to be devastating to many wines, though for select types of wines like Sauternes, Tokaji Aszu, and Spätlese German Rieslings, the presence of this fungus is actually highly desirable.

Botrytis cinerea infections result in withered grapes and can lead to a finished table wine with off-flavors and aromas. Not only does this reduce the desirability and quality of the finished wine, but it ultimately leads to significant economic losses for the winery.  On the other hand, in other wines like the ones mentioned above, the presence of Botrytis cinerea is actually desired, since the infection is partially responsible for the desired flavors and aromas of these finished dessert-style wines.

Another type of wine that relies on withered grapes for its quality is Amarone. Unlike Sauternes, Tokaji Aszu, and the like, Amarone grapes must be withered by drying and not via infection by Botrytis cinerea.

One problem arises is that it is rather difficult to tell the difference between grapes that are withered on their own versus grapes that are withered due to Botrytis cinereainfection. Since Botrytis cinerea is known to alter the chemical composition of Amarone wines, having the ability to distinguish between infected and non-infected grapes would be extremely helpful in producing desirable Amarone wines.

A new study in the journal Food Chemistry has taken a novel approach to distinguishing between infected and non-infected grapes by evaluating the individual proteins in both and comparing them to determine if certain proteins may be used as infection markers for possible use in real-time vineyard or winery assays.

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Best practices in malolactic fermentation (MLF) management

MLF in process.

Malolactic fermentation is an integrated part of winemaking which cannot be ignored. It can however be beneficial or detrimental and it is important that winemakers are well informed about it in order to make the right decisions. The execution of the decisions is also important to ensure that the required results are obtained in the wines.

Three different MLF genera, Oenococcus, Pediococcus and Lactobacillus, can convert the malic acid in wine into lactic acid. Only one Oenococcus species, but different Pediococcusand Lactobacillus species occur. Oenococcus oeni usually dominates because it has a higher resistance against the conditions occurring in wine. It is also the most desirable bacteria for MLF in wine because it can develop pleasant characteristics in wine while other species can cause spoilage like mousiness, sweaty and sauerkraut characters.

The end result of MLF is the decrease of the fixed acid concentration and increase in pH of the wine. The pH can increase with 0.3 or more units. The pH increase can however create favourable conditions for undesirable malolactic bacteria. Desirable MLF is usually acceptable in cool regions with a high fixed acid concentration to create a better balance in wines. Seeing that nutrients in the wine are also utilised during the process, such wines will be more stable against potential spoilage bacteria. It is not only as result of the utilisation of the nutrients, but also possibly due to the formation of toxins by the lactic acid, which can inhibit the growth of the spoilage bacteria. As result of the formation of other compounds during MLF the flavour profile and mouth feel of wines can also change. Diacetyl, which exhibits a buttery character, is an important compound formed during MLF. Its formation is influenced by the bacteria species, inoculation concentration of the MLF pure cultures, duration of the MLF, temperature, oxygen, pH and yeast lees contact. Ester compounds which can influence the wine flavour positively can also be formed during MLF.

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