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New World Wine Maker Blog

Sensory evaluation of mouthfeel in wine

by Renée Crous, Valeria Panzeri & Hélène Nieuwoudt

Sensory panels often avoid the evaluation of mouthfeel sensations in wine, since it implies (for many non-wine experts) complex, and abstract concepts. However, mouthfeel is an important dimension of wine quality, and it is, therefore, necessary that these properties are also included in routinely sensory tests. In our recently completed Winetech funded research project IWBT W13/02, “Rapid descriptive sensory methods for wine evaluation – special focus on further optimisation of rapid methods and streamlining of workflow”, we have developed two useful protocols for the assessment of mouthfeel in wine that can be used by sensory panels in the industry and research. This article describes the protocol that is based on the classic descriptive analysis (DA) method. In line with the objectives of project IWBT W13/02, we also optimised a rapid sensory method, polarised sensory positioning (PSP) to evaluate mouthfeel in wine. The rapid method does not require a trained DA panel and can be completed in shorter sessions. The protocol for the rapid method is discussed in a subsequent article.

What is meant by mouthfeel?

Mouthfeel refers to the sensory perceptions experienced in the mouth when a wine is consumed. Wine judges often describe wine as “full and round with good concentration, and length”, thereby implying that the product has good mouthfeel properties. While these phrases are commonly used in the popular media, people differ in their understanding of what exactly is meant by them. In scientific publications, several terms are grouped under so-called in-mouth sensations; these include fullness, heat, complexity, balance, length and mouthfeel.

Evaluation of mouthfeel by sensory panels

It is a challenging task to train a sensory panel to evaluate wine mouthfeel sensations. DA is one of our most accurate sensory test methods and provides two important outputs. Firstly, all the sensory properties that are perceived in a set of wines are identified and named by a panel of trained tasters. Secondly, panellists also score the intensity of each property on a line scale (ranging from 0 to 100, for example).

Physical standards are used to train a panel for the first task (identification of sensory properties). For example, a fresh lemon can serve as a standard for the lemon character in wine aroma. It is clear that all the panellists must have agreement on the sensations of the lemon character, as well as the particular word that describes the specific character, before the panel can proceed to assess the wines. With abstract concepts, such as length, complexity, and balance, there are no so-called physical standards, and an alternative plan must be made during training of the panel.

Another major challenge is to calibrate panellists to rate the intensities of the mouthfeel sensations on a line scale. It speaks for itself that the line scale must be used consistently by different panellists and on independent sets of wines; otherwise, comparative studies are not possible.

To illustrate these challenges: in this Winetech project, we wanted to evaluate the mouthfeel sensations of old-vine Chenin blanc wines (produced from vines 40 years and older) with the DA method. It is well known among wine experts that the old-vine Chenins have much more complex mouthfeel properties, compared to some younger vine Chenins. For panellists to use the line scale consistently to showcase these differences, they need to have in-depth experience and knowledge of the entire product category. This is seldom the case. Also in dealing with this challenge, adjustments had to be made to the standard DA protocol …

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MEET RUDGER VAN WYK – WINEMAKER AT STARKE-CONDE WINES

Q. When and where were  you born ? 

“ I was born in 1991 in George in the Southern Cape. Not quite in winemaking territory.”

Q. Where did you study and what qualification have you got ? 

“I studied at the University of Stellenbosch where I achieved a BSc Viticulture and Oenology degree.”

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

“No. I use what I was taught and have learned since then in various cellars. All well tried   good winemaking practices.”

Q. How involved do you get in the Vineyard ? 

“I try to spend as much time as I possibly can in amongst the vines as that is where a great wine begins. “

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

“I have cabernet sauvignon at top of my list but Sauvignon blanc and Chenin blanc are about tie for top with cabernet. However I find all our varieties  a joy to work with , because  each varietal is unique in it’s own way.”

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

“Abrie Beeselaar and Jose Conde , with their out of the box thinking have been a great influence. I found my visit to Burgundy to be a region  so very inspiring just to see the passion and love they have for their wine.”

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

“Inspiring others to follow their passion and work hard in what they love. We as winemakers will always  be in search of making the perfect wine, so when the day arrives (if it arrives) I will re-answer the question !”

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

“No secrets  but follow your gut and always be in sync with Mother Nature.”

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

I’ll  try to utilise it as a tool in the winemaking process to enhance the quality that nature gives us, but I strongly believe in the grape doing it’s natural thing.”

Q. What has been your history to get you to where you are ?

“I started my first harvest at Uitkyk wine estate, as an intern during  my final year of studies at University of Stellenbosch. The year after  I became a Capewinemaker Protégé, where I started at Kanonkop, under the guidance of Abre Beeselaar. I moved to Ntida wine estate in my second year, to learn more about cool climate winemaking.  In that year I was lucky  to do a harvest in Burgundy, where I finally fell in love with wine  and where that passion still drives me to this day. With all this experience I was taken on by Starke Conde where I have been given the opportunity to put it all into practice.  I sincerely believe that life set me up to get to where I am and to be working with the varieties I love.”

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When in Drought

“Rain, rain go away, come again another day”, I remember singing these words as a child, while staring at the drenched playground outside. Thick clouds, the pitter-pattering of rain against the window sill and  misery was all that accompanied those wet days as I looked towards the garden through the water-tinted glass. Fast-forward 15 years, and here I sit, staring out of a sun-dried window, searching the horizon for any sign of those heavy grey clouds.

South Africa is no stranger to drought, we’ve been experiencing these “dry-spells” over the decades, with increasing frequency since 1997. Although it is true that we produce some of our best wines under a little bit of (water) stress, how much can the vines really handle? How much can we handle?

In 2009, 2015 and 2017 South Africa saw some of its best vintages, with wines scoring well into the 90s (Wine Spectator). Stats have also shown that our overall harvest has actually increased by 1.4% from 2016 to 2017 (VinPro), which was not the overall expected outcome following the 2016 dry period. Could water stress be responsible for the slight increase, or are we perhaps still trying to use every last drop of water while it’s still available to us?

Recently, water stress has been emphasised in both our Soil Science and Viticulture courses. Research, evaporation minimalization, efficient irrigation scheduling and the science behind water stress in the vine have especially been highlighted. However, the costs and expenses involved in the implementation of drought control strategies seems to have slipped out of our teaching somewhere.

I only realised this when visiting a well-known rootstock plantation in the Paarl/Wellington region. One of the viticulturalists posed a question to our class: “Wat kan ek doen om waterverbruik te verminder (What can I do to reduce water consumption)”. Having just been taught this in Soil Science 344, many of us were eager to jump at the opportunity to share our new-found knowledge, oblivious to the trap he had set for us. He showed us that it is easy to think of a solution, however the costs implicated in the implementation of the best solution prove to be a difficult hurdle to overcome. This unfortunately leaves many farmers, in the wine industry and other agricultural sectors, with a very limited set of options on what seems like a very long list of solutions.

“How would you advise a farmer on how to manage his crops in such a way as to minimise the effects of drought and evaporation in the vineyard?” – This is a typical example of a test question or class discussion topic that a third-year student would be expected to answer. Answers would run along the lines of the use of mulches (plastic or organic), the installation of micro-drip irrigation systems, the regular measuring of soil water content using a tensiometer, vine water stress monitoring using a pressure bomb, installing irrigation lines beneath plastic, installing a wind break, the use of netting, the use of drought resistant rootstocks…the list goes on. These all seem like logical answers to a student, who has no idea on how to budget.

I took a drive through Stellenbosch recently, and the reality of the situation unfolded before my eyes. Vineyards are being pulled up, left to sprawl out through collapsing trellising systems and farms are being sold and auctioned off. A harsh reality for a youngster like me to face, is that more often than not, farmers are victims of unforeseen circumstances like drought, fire and flooding (wouldn’t that be lovely? – just not during harvest, please!). What can we expect for the 2018 harvest with the conditions ever-worsening and the expenses forever increasing? We can hold on to hope and faith in the mean-time; I hope that our rain will come soon, and I have faith that our beloved vines will cope if it does not.

Dry-spell feels like an appropriate word to use, doesn’t it? The upside of feeling like we are being bewitched by drought, is that any spell can be broken. A beam of light does shine through the current crisis, our yield has not yet seen an overall decline and our wine quality is still improving. Our red wines, in my opinion, have seen few better vintages than our drier years.

Why is this? Well, if water stress is applied at the right stages of ripening, berry metabolites and anthocyanins as well as other crucial wine components begin to accumulate into the berry. The vine goes into, what I like to refer to as an, “Oh shoot, ek gaan vrek” stage, meaning most of the vines reactions are pushed into a survival or reproductive mode. This could very well be a contributor to the deeper colours as well as the more full-bodied texture and mouthfeel of our fruit-packed wines.

Moving forward, I think the South African wine industry is going to experience a major shift in white wine production due to the drier conditions, focusing on a drier yet more tropical fruit driven style with slightly higher alcohol levels. White wines in particular, may need some kind of acid adjustment to reach a desired level of acidity due to the lower natural acid levels in ripe grapes. Red wines however, may become much darker and may require less skin content due to the higher anthocyanin accumulation at phenolic ripeness. More full-bodied, heavier and fruitier (dark berries and red fruit) driven red wines can be expected, adding more character to the wine and its complexity.

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Catch a whiff…

The total acidity in wine consists of two main components; non-volatile acid (including malic acid and tartaric acid) and volatile acid (VA). Volatile acid comprises of a group of volatile, organic, steam distillable acids. Concentrations mostly vary between 500 to 1000 mg/L, with almost 90% of volatile acidity consisting of acetic acid. The rest is mostly propionic- and hexanoic acid, as well as other fatty acids from yeast and bacterial metabolism, as well as ethyl acetate.

The most common VA concentrations in wine are around 0.4 g/L, with a legal limit of 1.2 g/L (see Table 1 for legal limits). The sensory threshold value in red wine is approximately 0.6 -0.9 g/L. whereas low, almost unnoticeable levels add to aroma complexity. With regards to the sensory attributes of VA; it contributes to the taste intensity of non-volatile acids and tannins, while the perception of VA itself is masked by high concentrations of sugars and alcohol. Acetic acid smells of vinegar, while ethyl acetate smells more like bruised apple and Cutex remover.

Volatile acidity production takes place mainly due to the oxidation of ethanol or the metabolism of acids/sugars. Ethanol is the primary energy source for acetic acid bacteria (AAB). Acetic acid bacteria are microscopic, single-cell organisms with enzymes included in their cell walls. The most common AAB present in wine include Acetobacter aceti, Acetobacter pasteurianus and Gluconobacter oxydans. These organisms are aerobic and need oxygen for survival. Acetic acid bacteria have the ability to oxidise alcohol to acetic acid, which in turn will, via esterification with ethanol, be converted to ethyl acetate. Ethyl acetate possesses a lower sensory threshold value compared to acetic acid and both acetic acid and acetaldehyde (a by-product of ethanol oxidation), are toxic to Saccharomyces cerevisiae and can contribute to sluggish- or stuck fermentations.

 

Origin and mechanism of oxidation…

During fermentation, the possibility of VA production is increased through the following practices: high risk must, risky winemaking practices and poor management of cellar conditions. Sources of VA after fermentation include cellar practices with specific focus on barrels: the amount of headspace, barrel age, oxidation and sanitary state of the barrels. Most AAB infections will take place in the cellar itself; mainly due to low acids and sulphur dioxide levels, together with oxygen exposure.

There are various sources that can add to the VA concentration in wine; the most conspicuous being:

  1. wild yeast e.g. Brettanomyces, Kloeckera etc. and as a natural by-product of S. cerevisiae

    Acetic acid is produced as an intermediary product of the pyruvate dehydrogenase metabolic pathway. This metabolic pathway is necessary and responsible for the conversion of pyruvate to acetyl-CoA. Last mentioned is imperative for anaerobic processes like lipid biosynthesis. This reaction is catalysed by alcohol dehydrogenase, whereby acetic acid is formed via the oxidation of acetaldehyde (produced from pyruvate during fermentation).

  2. lactic acid bacteria (LAB) during fermentation

    Heterofermentative LAB possess the ability to metabolise glucose (residual sugar), via the phosphoketolase metabolic pathway, and convert it to CO2, ethanol, acetic acid and lactic acid during malolactic fermentation. The first step in the citric acid metabolism produces acetic acid via citrate lyase activity, during which the conversion of citric acid to oxaloacetate, produces acetic acid.

  3. acetic acid bacteria

    Membrane-bound alcohol dehydrogenase oxidises ethanol to acetaldehyde. This intermediary is then oxidised further to acetic acid via membrane-bound aldehyde dehydrogenase.

  4. non-microbial source

    The chemical hydrolysis of wood hemicellulose, as well as the oxidation of gape phenolic compounds can result in the production of VA.

Factors that influence VA production…

  1. Sugar/osmotic pressure. Higher sugar concentrations result in a longer lag phase, which in turn lead to lower viability and growth potential of the yeast cells. Higher sugar concentrations together with low nitrogen levels lead to increased acetic acid concentrations.
  2. Fermentation temperature. Higher temperatures lead to higher VA concentrations.
  3. Yeast strain selection. The ability to produce VA id dependant on the specific yeast strain.
  4. The production of acetate esters e.g. ethyl acetate. This production is dependent on the yeast strain, the presence of indigenous yeast, fermentation temperature and SO2 concentrations.
  5. High initial acetic acid concentration. Rotten grapes, high sugar concentrations, pH and fermentation temperature at the start of fermentation will lead to increased acetic acid concentrations.
  6. A large bacterial population. High temperatures during storage of the wine (> 15°C), higher pH levels and lower alcohol and free SO2 concentrations, as well as poor cellar hygiene, will favour the survival of a bacterial population. 

Preventative measures…

  1. 1.     before fermentation:
  • monitor sugar and pH in the vineyard
  • do not mechanically harvest grapes that could be a potential risk
  • maintain sanitary conditions in the cellar e.g. equipment
  • use healthy grapes (avoid overripe)
  • do not excessively clarify the must, but a degree of clarification will reduce the indigenous microbial population

 

  1. 2.     during fermentation:
  • do acid adjustments if necessary to maintain low pH
  • maintain protective SO2 concentrations
  • use low VA-producing yeast strain
  • use sufficient nutrients during alcoholic fermentation
  • ensure fermentation is complete (no residual sugar / temperature fluctuations / re-inoculation)
  • reduce exposure to oxygen, but keep in mind that oxygen is necessary for alcoholic fermentation, as well as colour stabilising tannin reactions in red wine, so a degree of oxygen is required

 

  1. 3.     after fermentation:
  • inhibit malolactic fermentation with lysozyme if necessary
  • remove wine from yeast lees
  • adjust free SO2 levels to 40 ppm
  • ensure that wine is being stored in full containers
  • ensure sufficient sanitary state of barrels
  • correct usage of barrels
  • regular top up of barrels
  • bottling practices are important e.g. membrane filtration

 

Conclusions…

As mentioned above, there are a variety of preventative measures, but all these techniques are irrelevant if a winemaker sits with a high final VA concentration in his wine. Correctional options include blends, reverse-osmosis and nano-filtration.

Refrences…

1. How to diffuse a volatile situation. Zoecklein et al. 2005.

2. The origins of acetic acid in wine. M. Lambrechts.

3. Volatile acidity in wine. R. Gawel.

4. Current vineyard and cellar events. Sources of volatile acid formation in wine and potential control measurements. C. Theron.

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Creating Hybrid Wines True to Style

Over the years, I’ve noticed that it’s easy for wineries to fall subject to – what I like to call – the “ice cream syndrome.” In this case, one varietal wine is made for each wine grape variety brought into the cellar. Soon, a wine list in a tasting room can feel a bit like a list of ice cream flavors on an ice cream shop menu:

  1. Chardonnay
  2. Grüner Veltliner
  3. La Crescent
  4. Cayuga
  5. Cayuga Reserve
  6. Moscato
  7. Pinot Noir
  8. Cabernet Sauvignon
  9. Cabernet Franc
  10. Cabernet Franc Reserve
  11. Chambourcin
  12. Noiret
  13. Chancellor
  14. Concord

The list can go on and on.

Listing the variety name on a wine label has its benefits. Many fruit wines, obviously, would benefit from a name that reflects the fruit the wine is made from. Additionally, American consumers tend to identify with many wine grape variety names on a wine bottle. This is especially true when names are well-known like Chardonnay, Cabernet Sauvignon, Moscato, etc.

However, what about French American Hybrid wine grape varieties? In some of my previous travels, I heard local grape growers and winery owners reject the integration of more hybrid wine grapes because they found them difficult to sell to consumers. There is lots of reasons that may contribute to this including

  • Unfamiliarity with the name of the variety grape/varietal wine,
  • Prestige leading to other wine selections,
  • Worry to try new things,
  • Dislike for another winery’s wine with the same varietal wine, or
  • Poor wine production for that wine grape

Nonetheless, hybrid wine grape varieties are often needed in wine regions outside of the primary western wine-producing regions in the U.S. Through my travels, I’ve found consumer acceptance of these varieties varies from state-to-state and region-to-region.

What is Wine Style?

From a wine sensory perception, many hybrid grape varieties produce wines of similar style when they are produced with routine processing techniques. A wine style often describes the wine’s color, mouthfeel and aromatic composition. Most wines can be grouped into a few select wine styles regardless of where the wine is produced. Looking at wine style pulls away from classifications that focus on wine grape variety and provides a broader perspective in looking at your wine portfolio.

For example, in the list above, when grouped by varietal name, there are 14 different wines. When grouped by color, however, there are two groups (the first six are “white” wines and the remaining eight are “red” wines). When we start to look at a wine portfolio, or tasting list, by groupings or classifications, we can better identify where there are redundancies in production. This practice can help improve wine production efficiency, allocate gaps in the portfolio, and contribute to winery branding techniques.

Focusing on hybrid grape varieties, many retain their acidity through processing and are deficient in a tannic mouthfeel compared to their Vitis vinifera(e.g., Chardonnay, Cabernet Franc) cousins. The reds often exude a bright red, sometimes purple hue. Many of the whites often have somewhat neutral aromatics, bursting of lots of fresh citrus flavors. While there are always exceptions, the similarities among the varieties, compounded with unique wine names that are not common among the wine market, can often lead to consumer confusion.

Improving Hybrid Grape Variety Winemaking

Therefore, I’ve been working with a few of my clients in reviewing their hybrid wine programs by tasting through the finished-wine portfolio. The certifications I’ve received in wine education and tasting exercises that many sommeliers use allow me to identify wines that taste similar in texture and aromatics, or a combination of both. Additionally, in working with the winemaking team, I find we can often group three or more wines into the same style.

This practice allows us to isolate where there may be stylistic gaps and re-evaluate the production focus for a given grape variety or group of varieties.

The same is also true if a “new” wine grape variety falls into the winery’s lap. What can you make of that variety (other than the same-old processing techniques and putting a varietal name on it)? I can provide insight on different wine styles appropriate for the variety, or recommend blending options before grapes are made into wine. This can provide insight and direction for processing, which can ultimately improve cellar efficiency and fill in tasting menu gaps.

The benefit of this practice also allows me to work with clients and introduce them to new wine styles for a given wine variety. This is a very useful practice in getting away from varietal names and creating wines with unique labels that may have beneficial marketing advantages.

Truthfully, we can do this with V. vinifera grape varieties, too!

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LOUISE VAN DER WESTHUIZEN – WINEMAKER AT MOUNT VERNON

Q. When and where were you born ? 

With engaging smile “I am just a baby and born a Vaalie ! I was born on 11th June 1991 in Krugersdorp. My folks moved to Cape Town in December 1997, just before I started school. I believe it was one of the best decisions they ever made !”

Q. Where did you study ? 

“I did a BscAgric Viticulture and Oenology at University of Stellenbosch and graduated in 2014.”

Q. what made you do winemaking ?

“My folks had wine with dinner and would allow the kids to have taste. I became intrigued with the way different cultivars differed in taste and was different from region to region. So it was partly curiosity and I had always enjoyed the sciences also Die Burger had a weekly segment on wine which I was reading when I did matric. So it seemed that was what I was going to do”

Q. Do you consider your approach to winemaker different to others ?

A bit bashful in reply “I believe that wine should be an expression of the nature of the grape. Bring out the best in the grapes and you will get amazing quality. You don’t have to force it into a style.”

Q. How involved do you get in the vineyard ?

Now a bit serious “Not as involved as I would like, although I do work very closely with our viticulturist.”

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

“I love working with  Bordeax varieties, but the aromatics, Gewurztraminer and Weisser Riesling, are wonderful and tricky to work with.”

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

Without hesitation “Etienne Louw, of Altydgedacht. He was my first mentor in the wine industry and taught me how to work with a whole lot of different cultivars and how one can make brilliant wine in a primitive cellar !”

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

With a cheeky smile “Ask me again in a few years !”

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

With that cute smile again . “Slow malolactic fermentations may benefit from the use of patio heaters in winter !!”

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

Back to serious mode:  “Modern equipment does simplify things and speeds the process up, but are not essential.”

Q. What about the future ?

“I can’t talk about the future without taking a step back. After school I went to Germany to au pair and that was when the idea of becoming a winemaker really struck. I applied for a university  place and was accepted to start the next year, 2011. While studying I started running and completed my first Comrades Marathon in my final year, while busy with an internship at Altydgedacht in Durbanville.  After the race I actually stayed in Durban for a while to help with marketing before I returned to the Cape in 2015. I was a harvest intern at Rupert and Rothschild which gave me the opportunity to work with  amazing equipment and wines ! After that I was appointed as Cellar and Winemaking administrator at Beyerskloof for almost two years. I started at Mount Vernon in July 2017.

For now I am mostly focusing on the coming harvest , 2018,  and planning of a new cellar which is a great opportunity for me.” After some thought and then with that great smile “I have a few personal goals to reach, including, hopefully completing my fifth Comrades.  My dad finished his 40th this year !!”

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