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New World Wine Maker Blog

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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A day in the life of a ‘pre-exam’ new world winemaking student

By Geena Whiting.

Going through university we come across many different study techniques, and one of the most recommended ways of indicating your true knowledge of a subject is to try and explain it to someone. I have a massive test coming up and between you and me I am very nervous about writing it, it is on Malolactic fermentation and it is not my strong suit, so please allow me to try and explain it to you so that I can pass my test.

Malolactic fermentation is the breakdown of malic acid to lactic acid by bacteria. There are three metabolic groups that the bacteria fall under: Obligate homofermentitive, Obligate hetereofermentative and Facultatively heterofermentitive. The major bacteria O.oeni we use belongs to the obligate heterofermentative group, they posse the phosphoketlase enzyme and ferment glucose/fructose to lactate, ethanol, acetic acid and CO2.

The other common bacteria is L.plantarum species, these belong to the facultatively heterofermentative groups. It ferments glucose/fructose via the EMP pathway; however glucose represses the enzyme of the phosphoglyconate pathway and therefore doesn’t increase the volatile acidity of the wine.

Enough about the tiny details (That’s a microbiology joke because bacteria are small)

How does malic acid fermentation impact wine sensory attributes?

Aroma: there is an improved fruitiness, butteriness and a reduced vegetative character.

Taste: it’s less acidic than the original, a creamier and fuller palate and more complex flavours are produced.

Mouthfeel: there is better structure and a more balanced wine.

Colour: The impact on a heavy wine is limited but malic acid on cool climate wines or thin skinned grapes will cause a slight colour loss.

The aromas that the MLF produced can be described as buttery, lactic/yoghurt, nutty, yeasty, oaky, vanilla, fruity, caramel and toffee.

Where do the wine aromas come from?

Mainly the degradation of citric acid, citric acid exists in lower concentrations in wine (0.2-0.6g/l), the degradation begins when 2/3 of the malic acid degradation is complete.  Citrate is broken down by citrate lyase to oxaloacetate – this reaction also produced acetate which results in the increase of volatile acidity. Oxaloacetate is degraded to pyruvate and this gives rise to acetate, D-lactate, Diacetyl and 2,3-butandiol.

Diacetyl in low levels gives rise to toasty, nutty and yeasty characteristics, at medium levels you will smell buttery or butterscotch and adds complexity, high levels give you rancid butter and masks the fruity and vegetative aromas. This is what we want to see in a tasty Chardonnay.

2,3 – Butandiol at threshold levels of 600mg/l will give you fruity , buttery and creamy aromas.

Esters something that I don’t really think about in red wine, however MLF is a major process in making red wine… well, drinkable. Ethyl lactate is the most important ester; it provides the fruity, buttery and creamy mouthfeel. Ethyl hexonate gives off the brandy cherry flavour. Those beautiful floral aromas of some white wines are caused by ethyl octanoate. We all know that banana flavour in some pinotages, well that is caused by isoamyl acetate.

There are some downsides to MLF – this is the higher alcohol this can give rise to Isobutanol which gives off solvent and bitterness. Isoamyl alcohol which will give off that malty burnt flavour.
2- phenyl ethanol will bring those beautiful honey, spice, rose and lilac flavours.

The Strains also differ. O.oeni will increase the buttery aroma and will produce some VA. L.plantarum increases the fruitiness.

You also have to take into account when you inoculate: co-inoculation is when you inoculate during fermentation, this is great because the free sulphur and ethanol is low. You can use the temperature from fermentation. It will increase the fruitiness, less diacetyl is produced, the wine is less acidic. Sequential inoculation is when you inoculate after fermentation, this can be a problem with stuck fermentation because of alcohol, N sources are depleted and lysozyme are produced which kill the bacteria. There is no increase in Volatile acidity. It produces more buttery notes and the fermentation is easier to control.

Well thanks for your help, I feel much more confident about my test and I hope you have learnt something too!

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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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Back to the future – exciting and scary innovations in the wine industry

Written by Geena Whiting.

The industry we have committed ourselves to is forever expanding and growing. New ideas and innovations are on every horizon and the horizon is broad. Climb aboard the DeLorean with me and let’s see what the future holds.

Green Wine:

When talking about green wine, the slogan “going green” may cross your mind. While we encourage all sectors of agriculture to move to more sustainable and organic means, I am actually talking about wine that has a green colour.

There are many things associated with the colour green – nature, jealousy, the Grinch who stole Christmas and little green alien guys but wine? Surely that’s where we draw the line – its red, white or rose, the end of the story right? Wrong.  Vinho Verde the famous Portuguese wine, although the name literally means green wine the colour of the wine is actually white. What I am actually referring to is the Cannabis wine, much like the patented rooibos wine we have here in South Africa, the cannabis stalks are cold extracted and used as staves in place of oak during the wine making process. This leaves the wine with a green colour and a slight percentage of THC. Whether you want to legalize it man! Or not, you should defiantly give this wine tincture a try.

Blue Wine:

Everyone remembers those elegant blue creatures who took the world by storm, connected with nature and having a strong familial bond, naturally I’m talking about the Smurfs. Would you drink wine that is the colour of a smurf? Well there are a lot of people who do and this is how it’s made.

A blend of red and white wine is created and a rose colour is formed. Anthocyanin (The red colour pigment in red grape skins) is then added to the blend followed by the addition of indigotine plant dye. Which transforms the colour of the wine to neon blue, non-nutritive sweeteners are added and the wine is best served chilled.

So now when you are feeling sassy or sad there’s a wine to go with your mood!

Kosher wine:

Wine has been part of religious practices since the dawn of time, now there are ranges of wine that is prepared according to the requirements of Jewish Law. Zandwijk in Paarl, has gone above and beyond and become certified by the Cape Beth Din. All of the wines and juices are Kosher and Kosher for Passover. Whilst religiously adhering to the parameters of the Cape Beth Din, the modern and technologically advanced wine cellar allow for the wines to exhibit the terroir of South Africa.

This is untapped territory, will other farms take up the mantle and will we see more religious representation in the wine industry? Only time will tell.

Synthetic wine:

Also known as wine that’s not made from grapes.  A chemical product made in a lab consisting of all the  chemical compounds that make up wine – water, anthocyanins, flavonoids, tannins, fatty acids etc. It’s supposed to mimic expensive wines at a fraction of the cost so that the everyman will get to taste some of the most expensive wines without breaking the bank.

Do you think that this will catch on? Will there be space for both farms and labs on the shelves?

Vegan wine:

The push to become environmentally friendly is a growing trend that we should all get on board for. Vegan wine is becoming bragging rights for some farms and rightfully so. Wine can be made without the use of animal based fining products and still be as delicious and complex as it has ever been.  Basically it will taste the same and last just as long so why not be environmentally friendly too?

Wine in a can:

A recent article I read posed that while the more traditional wine drinkers opposed this idea, millennials love it. Speaking as a millennial, yes, yes we do.  Why shouldn’t wine come in a can, it’s much easier to recycle than these new plastic bottles and is more easy to transport than a big glass bottle. Sometimes we don’t want to have to finish the whole bottle and just sit back with a glass (a can) and drink our favourite drink. Whether this will catch on and become common place for every brand is doubtful, but it definitely has its place in the market and is better than plastic alternatives.

When your great, great, great grandchild has their first sip of wine what do you think the wine will look like?

For me, I hope that our traditional wines stick around like they have since the beginning but that does not mean there isn’t space for new ideas on the wine rack.

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Pruning Competition 2018

A short while ago, a discrete class pruning challenge was presented to us, wherein we each had to prune a row of what seemed like Shiraz vines gone rogue. After many hours (yes, some of us even took a few days) of snipping away at each vine, we finally managed to somewhat restore (or destroy…) the vineyard to a workable condition. These rows were then marked and judged according to skill, and the 6 pruners with the top scores were selected to represent Stellenbosch University at the Felco Pruning Competition in August 2018. Of the 6, the 3 candidates with the highest score were selected for or representing team while the other 6 were trained up – in case someone snipped a finger off, we’d need a backup!

The day of the competition had finally arrived, after weeks of training, our pruners were ready! The crisp morning air filled the lungs of the eager fourth year Stellenbosch students as we made our way down to La Motte’s vineyard. We were eager and ready to cheer on our three selected pruning champions as they prepared to take on the Elsenburg and CPUT students. Stellenbosch, being the underdogs for the last few years, had not lost all hope of winning, despite our formidable opponents.

The competition began with each competitor selecting a row, our three students (Cara Kroep, Anandi Theunissen and Francois Burger) were divided between rows 56 and 57. The supporting crowd (my fellow class mates and I) paced in anticipation, up and down along the outskirts of the two rows as we held on to our hopes for victory. The pruners filled the air with a snipping melody as the workers and students sped through the block, with only an odd ant’s nest or spider here and there to slow them down not much else stood in their way.

Anandi, painting a perfect picture of precision and focus as she made each cut, moved through her row, carefully analysing each and every bearer before making a decision. Francois sped through his row, being the first of the Stellenbosch students to finish his pruning, while making sure that each and every cut was smooth and clean. Cara, only slightly faster than Anandi, was calmly and quietly moving through her vakkies, also carefully looking at each and every point before making a cut. An ants’ nest, quaintly nestled between the two cordon arms, presented no challenge for Anandi, even when our Demi (student lecturer) poked the nest out of curiosity and all the ants came swarming out. She continued to prune despite the ant hoards marching towards her hands as she worked.

The class stood around, eagerly awaiting results; the heat was on, we had to finally show Elsenburg and CPUT that we’re not all about the science (not all the time anyways)! Our impatience grew as we waited for the judge to move through the rows, we had to know the results! After the marking and deliberation, we all sat down and munched on a few boerewors rolls and cold drinks, excitement and suspense buzzing between conversations, while the scores were tallied.

In the previous few years, Stellenbosch has had students place, but we have unfortunately never been able to out-compete the more practical Elsenburg and CPUT students. The pressure was on this year, all of the students came prepared for a challenge. We gathered around the quart yard, all holding thumbs for a win. Third place was called up, row 60, an Elsenburg student. Immediately our little strand of hope seemed to dwindle; second place was called up – row 59, also an Elsenburg student. By this point we had almost lost our hope to finally claim the title of 2018’s student pruning champion, “Row 57”, Jaco called. Nobody came forward, Anandi looked very confused for a moment, before three of the Stellenbosch students practically nudged her forward, excitedly telling her, “It’s you! It’s you!”.



At long last, Stellenbosch University had finally claimed the trophy! Our class all huddled around our three competitors, who all displayed extraordinary skills in the vineyard during the competition, our smiles all beaming. I can confidently say I know exactly who I am calling to come and help me in the vineyard one day! We were all incredibly proud of all 6 team members, who poured a lot of time and effort into preparing for the competition. Elsenburg and CPUT’s students also displayed remarkable technique in the vineyard, I was impressed by the speed and precision executed by all three of the competing institute’s students. Felco definitely gave us an amazing opportunity, allowing us to see students and professional pruners from around the country at work. I look forward to the future of viticulture and winemaking in South Africa, with such talented individuals leading the way.

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Meet Stuart Botha, winemaker at Tokara

Q.  When and where were you born ? 

“I was born in Durban, South Africa in 1985.”

Q.  Where did you study and what qualifications do you have ? 

“I studied winemaking and viticulture at Elsenburg Agricultural College, qualifying with a B.Agric Viticulture and Oenology in 2006.”

Q. Do you consider your approach to winemaking to be different to others ?  

With a smile “That is a really subjective question.  I wouldn’t say that I am wildly different. I do like to experiment though, and that is where new and interesting discoveries are made. I also like to stay on the forefront when it comes to new technology. If I can implement something to make better wines, I’ll do it. “

Q. How involved do you get   in the vineyard ? 

“Getting involved with the vineyard and having a good synergy between viticulture and winemaking are imperative. The two go hand in hand. So many stylistic outcomes in wines rely heavily on practices that take place in the vineyard. That being said, I like to be very involved in the vineyard.”

Q. Do you have any varieties you prefer to work with ? 

“I am a big fan of both Cabernet Sauvignon and Shiraz.”

Q. Have you been influenced by a particular winemaker or by a wine region ? 

“I wouldn’t say by a particular wine maker but I draw inspiration from other winemakers all the time, through general discussions and sharing of ideas.  It’s what makes the industry so great to be part of. I did two harvests in St. Emilion, France and that really did have a huge influence on me.”

Q. What would you consider your greatest achievement as a winemaker ?

“I have many achievements that I am incredibly proud of although winning the Trophy for the Best Shiraz at the International Wine and Spirit with my Eagle’s Nest Shiraz 2009 was a definite highlight.”

Q. What “secrets” have you “developed” that make your wines different to others ?

“I don’t suppose any really. I just do the basics as well as I can. “

Q. How important is modern winemaking equipment in your winemaking ?

“I have quite a modern cellar, and I am always looking for something that will assist me to make even better wines or even something new or different.  I believe that modern equipment and technology definitely play a role in making better wines. In the same breath, however, I am cautious not to take it too far, as it can sometimes lead to generic outcomes. It’s imperative to have a point of difference,”

Q. Anything else you would like to add ? 

“Following my studies, I joined Constantia Glen as an assistant winemaker. During my time there was when I journeyed to St Emilion to take part in two harvests. One at Chateau Bellefort Belclair and the other at Chateau Trianon. Where I obtained valuable experience. My first job as head winemaker was at Eagles Nest, where I was lucky enough to open their brand new winery.  I had an incredible ten harvests there and am proud to   have been part of growing the fledging winery into the incredible brand it is today.  While there I also explored the wine regions in Australia, France, Germany, Spain and Switzerland gaining knowledge and tasting extensively.”

Q. And now ? 

“In September 2017 I joined the winemaking team at Tokara on the Hellshoogte in Stellenbosch which is world renowned for consistently producing some of South Africa’s finest wines, It has been a fantastic start and I am thoroughly enjoy working with the full array of Bordeaux varieties in this ultra-modern winery.

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