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New World Wine Maker Blog - Technical Articles

The advantages and disadvantages of oxygen prior to bottling

By Charl Theron, Wineland Media.

“Oxygen can make or break a wine.” – Louis Pasteur. Oxygen is an integral part of life and plays an important role in different biological and chemical reactions.

Dissolved oxygen is the free molecular oxygen in solution and is expressed as milligram per litre (mg/L), parts per million (ppm) or percentage saturation (%sat). The extent of oxygen solution into wine during air contact is influenced by temperature, atmospheric pressure and the pH of the wine. Lower temperature and an increased atmospheric pressure favour the solubility of oxygen and higher pH decreases the percentage molecular sulphur dioxide, which limits the influence of oxygen as an anti-oxidant. At standard temperature and atmospheric pressure wine is saturated with oxygen at a dissolved oxygen concentration of 6 mg/L (

The general perception is that oxygen is detrimental for wines, although certain stages of winemaking exist where it can be beneficial, if managed properly. This includes the hyperoxidation of juice, the role of oxygen during the initiation of alcoholic fermentation and the micro-oxygenation of red wines.

The aim of hyperoxidation prior to alcoholic fermentation is to protect the resulting wine against browning or oxidation during the further winemaking processes. It is also stated that it can improve the shelf life of such wines. It comprises the enzymatic oxidation where oxygen reacts with certain phenol groups in the absence of sulphur dioxide to form yellow quinones. The latter compounds react further with oxygen to form brown coloured products, which precipitate and can be removed by racking. Wines made from such juice are consequently protected against further browning. The uncertain potential advantages of such procedure depend on various factors of which the vineyard and cultivar can play a role. Different opinions also exist regarding the influence of such practice on the sensory quality of wine.

Oxygen is essential for the multiplication of yeasts and formation of flavour profiles in the beginning of alcoholic fermentation. Most of the dissolved oxygen results from the crushing of the grapes, pressing of skins and rackings. Depending on the temperature, equipment and the executed processes it can even lead to the saturation level of oxygen at 6 to 9 mg/L oxygen. If insufficient oxygen is present in the juice it can lead to sluggish or stuck fermentations. This is as result of insufficient sterole formation in the yeasts. Sterole formation is essential for yeast propagation and after various generations of yeast propagation a shortage of oxygen may develop for it. Dissolved oxygen levels of 4 to 6 mg/L are required at the beginning of alcoholic fermentation to overcome this problem …


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How Touch Might Influence How A Wine Tastes

By Becca Yeamans-Irwin of The Academic Wino. 

There are a lot of factors that can influence the way wine tastes to someone.  From the lighting in the room, to the music you’re listening to, to what you’re eating, or to how you generally feel that day, there are a lot of outside stimuli that can change your experience with a given wine.

Some more recent research has focused on the sensation of physical touch, and has found that the flavors and overall acceptability of various food and beverages can be influenced by the texture of the packaging itself. For example, one study found that biscuits taken from a bowl with a rough surface tasted crunchier and harder than those taken from a smooth-surfaced bowl. Additionally, for a beverage example, another study found that hot chocolate and coffee tasted from a round cup tasted sweeter and “less intense” than the same drinks tasted from a cup with more angular features.

Dubbed as “sensation transference” in the 1950s, the theory is that someone’s feelings about a particular extrinsic characteristic (i.e. the texture of the packaging) can influence their rating of the actual product itself. In 2011, another study further defined this theory as “affective ventriloquism”, when sensation transference affects someone’s rating of a product (like food or beverages).

Touch itself is known to alter emotional responses in general.  Specifically, one 2013 study looking at blood flow in the brain found that touching fabric samples led to a calming response (decreased activity in the orbitofrontal cortex) compared to touching a sample of metal.

While research on sensation transference and affective ventriloquism is growing, according to a new study just accepted into the International Journal of Gastronomy and Food Science, there isn’t a lot of research done on how these theories impact perception of aromas, and specifically aromas in wine.

The overall goal of this new study was to examine how touch might influence the wine tasting experience, or more specifically, how touch may or may not influence both the taste of the wine as well as the aroma and mouthfeel …


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Brett + bacteria = worse, or better

By Erika Szymanski of The Wineoscope

Microbiology has gotten a lot wrong studying yeast and bacteria. We’ve assumed, until quite recently, that if a microbe doesn’t grow in a dish it’s not there. And that a microbe is either on/live/growing or off/dead. And that we can study microbes in isolation — “pure culture” — away from other species in little sterile dishes and expect them to behave normally. In all fairness, microbiologists have sometimes seen these as a problems, but have mostly just gone on this way, writing books about what we think we know.

DNA detection and sequencing technology is showing just how many bugs don’t grow in dishes — “high throughput” technology can document (theoretically) all of the species in a drop of [insert favorite liquid here]. That’s pretty routine these days. And we’re slowly beginning to study how mixtures of microbes — you know, the way they live in the wild — behave in the lab. Wine was a bit ahead of the curve here: microbial enologists have been studying the goings-on of spontaneous and mixed fermentations since the late 1980’s.*

Usually, mixed-microbe studies are about what grows where together. Occasionally, you can predict something more specific with a bit of logic and some scratch paper. That, plus a little knowledge of yeast and bacteria metabolism, leads to an interesting hypothesis: some malolactic fermentation bacteria should make Brett smell worse.

Brettanomyces bruxellensis (aka “Brett,” aka barnyard-stench spoilage yeast) creates its signature aroma by converting hydroxycinnamic acids (HCAs) naturally present in wine to smelly volatile phenols. This is a two-step process. First, an enzyme (a decarboxylase) converts HCA to a vinylphenol. Second, a different enzyme (a reductase) converts the vinylphenol to the volatile ethylphenol, including the Brett signature 4-EP and 4-EG.

But before that can happen, Brett has to be able to get to the HCAs. Many of the HCAs in wine are chemically bound to tartaric acid. Brett can’t use them if they’re bound. The HCA-tartaric acid bond spontaneously and slowly breaks, giving off free HCAs for Brett to use, but there’s theoretically a much bigger pool of pre-stink molecules that need only lose their acid first.

Some lactic acid bacteria — like the ones that commonly perform the malolactic fermentation (MLF) so important to most reds and a lot of white wines — can enzymatically split HCAs from tartaric acid. In theory, that should mean that some (but not all) MLF bacteria are Brett enablers. Wine + bacteria + Brett = worse smell than wine + Brett alone.

Building on previous research, a team at Oregon State University has made that more than a theory. Their recent paper (currently pre-press in AJEV) shows that some commercially available MLF strains make more HCAs available than others, AND that leads to Brett making more 4-EP and 4-EG,

The team only experimented with one strain of Brettanomyces, and they obviously couldn’t test anywhere near all of the MLF strains on the market, but this (plus the multiple studies that have come before it supporting the effects of lactic acid bacteria on HCAs) is strong evidence indeed that winemakers buying commercial bacteria for MLF may have better and worse choices if they’re worried about Brett.

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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.


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.


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.


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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