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New World Wine Maker Blog - Technical Articles

Assessing grape maturity for harvest planning

By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science

If just one adjective was chosen to describe the 2018 growing season to date, many of us might suggest ‘rainy.’ In many Pennsylvania regions, grape growers faced persistent rainfall for the majority of the summer. For example, in central PA, State College has had an accumulation of 29 inches (737 mm) of rainfall for the months of April through August.  Growers really had to be on top of their fungicide spray schedule and canopy management plans to minimize the risk of disease so that fruit will be healthy at harvest time. Recently, Bryan Hed and Jody Timer wrote blog posts that provided recommendations for late-season downy mildew control and insect problems. While the weather forecasted for harvest season is weighing heavily on the minds of many grape growers, a post-veraison task critical for a successful harvest is collecting grape samples to measure the progression of fruit maturity.

This article provides a brief review on what fruit ripeness parameters you should measure and how to collect berry or cluster samples to best assess fruit maturity. While this information could be particularly useful for new grape growers approaching their first vintage, experienced growers should review the information to ensure that they are using the best techniques for collecting representative fruit samples.

Harvest decisions

Grapes are typically harvested when they reach desired fruit quality parameters (e.g., sugar content, pH, flavor, color) which vary depending on the wine type or style the winemaker aims to produce. Grapes should be sampled periodically until harvest to monitor how parameters associated with fruit maturity (e.g., sugar, pH, organic acids, flavors) evolve through the ripening season. However, there are many other factors involved in selecting a harvest date, which may or may not directly relate to optimal fruit maturity. These factors include:

  • Fruit health condition (is the fruit deteriorating due to rot or other disease or insect damage?),
  • disease and insect pressure,
  • short and long-range weather forecasts,
  • available labor,
  • space available at the winery to process the grapes, and
  • type or style of wine that will be made.

What fruit ripeness parameters to measure

The evaluation of the overall fruit ripeness involves quantitative parameters (sugar content, pH, titratable acidity) but also measurements that go beyond analytical techniques(berry sensory analysis).

Quantitative measurements to determine grape ripeness:

The information reported below is adapted and summarized from the factsheet Determining grape maturity and fruit sampling written by Dr. Imed Dami, Ohio State University.

Sugars, organic acids, and pH are the primary indicators of technological or commercial grape maturitywhich is different from physiological maturity that occurs at or soon after veraison when seeds are ready to germinate.

Sugars: Sugars, specifically glucose and fructose, are the main soluble solids in grape juice. Sugar content is typically measured in degree Brix (°Brix); 1 degree Brix corresponds to 1 gram of sugar per 100 grams of grape juice. Desirable levels of sugar content are typically between 18 and 24ᵒBrix, depending on grape variety and wine style.

Sugar level is relatively easy to measure in the vineyard with a handheld refractometer ….

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Understanding Difficult Malolactic Fermentations

By Dr. Molly Kelly, Enology Extension Educator, Department of Food Science. 

As harvest comes to a close we have planned which wines will be going through malolactic fermentation (MLF). This article provides some information to assist you in dealing with a potentially difficult MLF.

Malolactic fermentation (MLF) is a process of chemical change in wine in which L-malic acid is converted to L-lactic acid and carbon dioxide. This process is normally conducted by lactic acid bacteria (LAB) including Oenococcus oeni, Lactobacillus spp. and Pediococcus spp. O.oeni is the organism typically used to conduct MLF due to its tolerance to low pH, high ethanol and SO2. Most commercial strains are designed to produce favorable flavor profiles.

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Although inoculation with a commercial starter is recommended, MLF may occur spontaneously. The lag phase associated with spontaneous MLF may increase the risk of spoilage organisms as well as the production of volatile acidity. Inoculation with a LAB culture can help avoid these problems by providing the cell population needed to successfully conduct MLF (more than 2×106 cells/mL). The compatibility of yeast and LAB should be taken into account since failed MLF may be due to incompatibility between these two organisms.

The key to a successful MLF is to manage the process and to monitor the progress. Although there has been extensive research on the MLF process, it may still be difficult to initiate at times. The possible causes of difficult MLF have been studied less extensively than those of stuck/sluggish alcoholic fermentation. In this article, factors that may influence the start and successful completion of MLF will be discussed.

The main chemical properties that influence MLF are well known: pH, temperature, ethanol and SO2 concentration. A study by Vaillant et al (1995) investigating the effects of 11 physico-chemical parameters, identified ethanol, pH and SO2 as having the greatest inhibitory effect on the growth of LAB in wine.

pH

Generally, LAB prefer increased pH’s and usually, minimal growth occurs at pH 3.0. Under winemaking conditions, pH’s above 3.2 are advised. The pH will determine the dominant species of LAB in the must or wine.  At a low pH (3.2 to 3.4) O. oeni is the most abundant LAB species, while at higher pH (3.5 to 4.0), Lactobacillus and Pediococcus will out-number Oenococcus.

Temperature

MLF is generally inhibited by low temperatures. Research demonstrates that MLF occurs faster at temperatures of 200 C (68˚F) and above versus 150C (59˚F) and below. In the absence of SO2 the optimum temperature range for MLF is 23-250C (73.4˚F-77˚F) with maximum malic acid conversion taking place at 20-250C (68˚F-77˚F). However, with increasing SO2 levels, these temperatures decrease and 200C (68˚F) may be more acceptable.

Ethanol

LAB are ethanol-sensitive with slow or no growth occurring at approximately 13.5%. Commercial O. oeni strains are preferred starter cultures due to tolerance to ethanol.  The fatty acid composition of the cell membrane of LAB can be impacted by ethanol content.

Sulfur dioxide

LAB may be inhibited by the SO2 produced by yeast during alcoholic fermentation. A total SO2 concentration of more than 50 ppm generally limits LAB growth, especially at lower pH where a larger portion of SO2 is in the antimicrobial form. Generally, it is not recommended to add SO2 after alcoholic fermentation if MLF is desired.

Some of the lesser known factors impacting MLF are discussed below.

Fatty Acids

MLF can be inhibited by medium chain fatty acids (octanoic and decanoic acids) produced by yeast. It is difficult to finish MLF when octanoic acid content is over 25 mg/L and/or decanoic acid is over 5 mg/L. Bacterial strains that tolerate high concentrations of octanoic and decanoic acids may be important in successful MLF. It is important to check your supplier regarding strain specifications. Yeast hulls may be added before the bacteria are inoculated (0.2g/L) to bind fatty acids. Yeast hulls may also supply unsaturated fatty acids, amino acids and assist with CO2 release.

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The Effects of Wine Bottle Closure Type on Perceived Wine Quality

By Becca Yeamans of The Academic Wino.

How a winery chooses to close a bottle of wine depends on a variety of factors, from function to consumer perception/marketing. While natural cork closures are the more traditional choice, there has been a lot of technological advancement in the closure industry. There are

many different kinds of synthetic and technological closures on the market, from cork-alternatives to screwcaps, many of which are designed to optimize oxygen ingress into the wine, as well as minimize or eliminate the presence of cork taint.  Despite these technological advances, many wineries still prefer to use natural cork for their closures, as from a marketing perspective, cork is associated with the highest quality according to the average consumer.

Though much is known about the technical differences between wine bottle closures, very few studies in the academic literature have looked at closure type from the consumer perspective, namely consumer associations between closure type and wine quality characteristics. Other non-academic studies have been performed regarding this topic – for example, one year ago, a study by Wine Opinions in conjunction with The Portuguese Cork Association and the Cork Quality Council, found that consumers preferred the natural cork closure as they preferred the tradition and “romance” of pulling of the cork ritual, and that 68% of participants felt wine closed with natural cork was of higher quality.

While there are many of these types of studies out there, there aren’t as many found in the academic literature.  A new study, accepted into the International Journal of Hospitality Management (and currently available online), aimed to add to these relatively small number of studies by examining how wine closure type affects wine quality perceptions by the average consumer.

Brief Methods

This study took place on the campus of Washington State University in 2013 and recruited a total of 310 people (though only 299 were used for statistical analysis). Participants included students, parents, faculty/staff, and other members of the community …

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Grapevine Shoot Chips: A Novel Alternative to Oak Chips in Winemaking

The use of oak barrels in wine fermentation and aging increases wine aromatic complexity and improves overall quality. Despite a higher price tag, this technique is often used for red and some white wine aging. Due to higher costs, and other factors, many have sought alternatives that can produce a very similar style/quality wine at a fraction of the price. Most of you are already familiar with the use of oak chips in wine.  Oak chips are typically made from wood already utilized for wine barrels, and undergo similar toasting treatments to provide the aromas, flavors, and aging characteristics desired. Because of the increased surface area available by the small-sized chips, winemakers don’t need to use very many oak chips compared to the size of the barrel that would be needed to achieve comparable results.

Another way to impart oak flavors into wine, which isn’t as common but has been studied a bit in the literature, is oak extract application on grapes or grape vines. While studies have shown this sort of treatment may produce similar aromatic and sensory characteristics in the finished wine as a wood-aged treatment would, it’s likely just a way to get a “flavor now!” response and not a functional aging ability.

Of course, there are many other oak alternatives utilized in commercial especially home winemaking, but I won’t go into that now.

One new study, currently available online and to be published in print in October 2018 in the journal Food Chemistry, aimed to add one more potential oak alternative to the winemakers’ arsenal that I wasn’t expecting: grapevine shoots. Partially a response to growing demand for oak barrel alternatives, and partially a response to the amount of physical waste generated after the grape harvest, a team of Spanish researchers aimed to evaluate the use of grapevine shoot “chips” (toasted) as an alternative to oak chips in winemaking …

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50 SHADES OF ROSÉ

Oh my…it’s so big….the growth of rosé wine popularity that is.

rosé
ˈrəʊzeɪ/
noun

any light pink wine, coloured by only brief contact with red grape skins.

“a glass of rosé”

Such a simple and one-dimensional definition for a complex, diverse and let’s be honest, sexy product. Pale onion-skin orange to almost purple; still, semi sparkling or sparkling; sweet to bone-dry; this genre of wine is as diverse as the cultivars you can use to make it.

The production numbers at a glance…

  1. global rosé production: approx. 25 million hL
  2. accounts for approx. 10% of still wine production
  3. 80% of production: France, Spain, United States and Italy

Increase in rosé production since 2002:

  1. South Africa: 200%
  2. Chile: 400%
  3. Australia: 450%

The consumption numbers at a glance…

  1. global rosé consumption: approx. 23 million hL
  2. 20% increase in rosé consumption since 2002
  3. France and US: consume approx. half of global rosé production

Increase in rosé consumption since 2002:

  1. United Kingdom: 250%
  2. Sweden: 750%
  3. Canada: 120%
  4. Hong Kong: 250%

Call it what you will…a French rosé, a Spanish rosado, an Italian rosato or a German roséwein…this blush-coloured phenomenon has shaken off the frumpy “sweet and unsophisticated” persona and slipped into something a little bit more comfortable…the new crisp, dry and fruit-driven style of rosé taking the market by storm.

The three major rosé production methods, maceration, saignée and blending, will provide you with different styles and colour of rosé wines.

During the maceration method, the grapes are destined primarily for rosé production and the maceration period can differ significantly according the shade and intensity of rosé being produced. This method is popular for commercial rosé production. The saignée or bleeding method sees you remove some of the juice from the red wine production process to produce rosé and at the same time intensify the colour and tannin concentration of the red wine being produced. This method usually results in darker and more savoury rosé styles. The final method, blending, is less popular and more regulated in certain rosé producing areas like France, where white wines are enriched with coloured musts to produce a rosé wine. A less common method is that of vin gris, where the rosé is produced by the immediate pressing of red grapes without any skin contact. This method is generally practised on lighter coloured varieties like Cinsaut, Gamay noir, Pinot noir and Grenache.

So what makes a good rosé? The style that is gaining in popularity is that of a clean, fruit forward wine with crisp acidity, where freshness and complexity is balanced. To produce this, there are a couple of key factors:

  1. Light touch
  2. Gentle handling of the fruit
  3. Short and light press cycle
  4. Cold settling
  5. Fermenting at cool temperatures to retain aromatic compounds
  6. Use a dedicated yeast and enzyme combination to enhance bright, rich, fruity flavours

The style of rosé’s produced with these different methods, despite coming in a veritable rainbow of pink shades, can vary anywhere from light and mineral-like, to round and floral and rich and savoury. From a visual point of view, you can expect anything from a pale onion-skin hue, interspersed with salmon, rose, coral, watermelon coloured wines, all the way to the cherry and ruby red offerings. Rosé really has an outfit for every occasion…

With so many styles of rosé, differing in colour, sweetness, bubbles and aroma, you are sure to find the one that makes you blush!

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Non-Saccharomyces yeasts, MLF and Chardonnay flavour

by Heinrich du Plessis & Neil Jolly. 

This study follows similar studies done by us on Chenin blanc and Pinotage. The aim of this study was therefore to determine the effect eight different non-Saccharomyces yeast strains had on MLF and Chardonnay flavour.

Introduction

Wine production includes two important fermentation processes, i.e. alcoholic fermentation conducted by yeast, and malolactic fermentation (MLF) conducted by lactic acid bacteria (LAB)1. The yeasts drive alcoholic fermentation by converting sugar to alcohol, carbon dioxide and other secondary compounds that affect the aroma and taste of wine.1,2Malolactic fermentation contributes to further flavour complexity and microbiological stability of the wine, as well as the reduction of total acidity. During MLF, l-malic acid is decarboxylated to l-lactic acid and CO2. White wines do not usually undergo MLF, but it is desired in the production of certain full-bodied white wines.3,4

At the start of alcoholic fermentation, a large number of non-Saccharomyces species may be naturally present in the grape must, but the final stage of fermentation is usually dominated by alcohol-tolerant Saccharomyces cerevisiae strains.1,5 Non-Saccharomyces yeasts have different oenological characteristics to S. cerevisiae and they have been shown to enhance aroma and improve complexity of wines.5,6 During alcoholic fermentation, both Saccharomyces and non-Saccharomyces yeasts deplete the nutrients found in wine. These deficiencies, combined with toxic metabolites produced by the yeasts, can inhibit the growth of LAB.1,7,8 Despite considerable research, MLF remains a difficult process to initiate and control.9 The interaction between non-Saccharomyces yeasts and LAB is another factor that needs investigation.

Materials and methods

Eight non-Saccharomyces yeast strains (one Candida zemplinina, two Lachancea thermotolerans, one Metschnikowia pulcherrima, one Hanseniaspora uvarum and three Torulaspora delbrueckii) were used in mixed fermentations with one S. cerevisiae wine strain. Yeast strains were commercially available cultures or were obtained from the ARC Infruitec-Nietvoorbij microorganism culture collection. Yeast treatments without malolactic fermentation (MLF) and in combination with simultaneous MLF were investigated. A commercial lactic acid bacterium culture was used to induce simultaneous MLF. In total 18 treatments were evaluated in triplicate, and the Chardonnay wines produced with S. cerevisiae with or without MLF, served as the reference treatments. A standardised small-scale winemaking protocol was followed at an ambient temperature of 15°C. After completion of MLF, wines were bottled and subjected to descriptive sensory evaluations four months later.

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