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New World Wine Maker Blog

Understanding and measuring tannins in red wines

by Jose Luis Aleixandre-Tudo, Mihaela Minhea & Wessel du Toit 

The importance of phenolic compounds on wine quality require methods that accurately measure the tannin content.

Tannins are phenolic compounds that play an important role in the astringency perception of red wines. Tannins also are very complex molecules with different sizes and conformations. The decrease in the astringency intensity during ageing is due to different phenomena, including cleavage reactions (appearance of smaller less astringent molecules), precipitation from solution, due to insolubility situations, conformational arrangements (shape of the tannins molecule) and interactions with other components (such as anthocyanins). Precipitation based methods (BSA and MCP tannins assays) are highly suitable for routine tannin analysis. Both methods positively correlate with each other and also with the astringency intensities measured by a sensory panel.

Introduction

Tannins are phenolic compounds that are involved in red wine mouthfeel attributes. They are also thought to play a very important role in the astringency perception. When drinking red wine, the tannin compounds interact with the salivary proteins, creating a macromolecular complex that precipitates from solution and causes a drying and puckering mouthfeel sensation, also known as astringency.1 The intensity of this feeling depends on many factors. The size and conformation of the molecules, the combination with other wine components and the levels found in wine define the astringency intensity.

It is also known that the wine astringency decreases over the ageing process.2,3 This behaviour that was initially attributed to a decrease in the total tannin content present in the wine, is nowadays ascribed to different phenomena. Starting with the assumptions that tannins polymerise during ageing and that the ability of the tannins to elicit astringency increases with tannin size (i.e. the bigger the molecule, and the higher the number of sites available to interact with the salivary proteins, the higher the ability to combine and precipitate proteins)2 other phenomena that explains the decrease in the astringency intensity needs also to be playing role. First of all, cleavage reactions, which means large tannin molecules break down giving rise to smaller, less astringent tannins, have been proposed by some researchers.4 Moreover, molecular conformational arrangements have also been identified as a possible reason.5 Bigger and larger tannin molecules can also be too bulky (which means that due to the molecular conformation, the active binding sites are not available to interact with the salivary proteins). In this specific scenario larger tannin won’t give rise to an increased astringency perception. It is also well accepted that anthocyanins play an indirect role in wine astringency. The anthocyanin-tannin molecules cause a reduction on the ability of the newly formed polymeric pigment to interact with salivary protein thus reducing astringency (phenomenon that could also be related to the abovementioned conformation rearrangement scenario).6 The later phenomena together with the precipitation of tannins from solution, due to insolubility conditions, may explain why the wine astringency softens during ageing.

Tannin measurement by acid hydrolysis

The quantification of tannins has been challenging researchers over the past years as these compounds are of a very diverse nature, a fact that makes it difficult to estimate their concentrations. However, a number of methodologies are currently available for the measurement of the wine tannin levels. A method that has been commonly used for a long time exploits the ability of the tannin molecules to break down in a heated acid environment (acid hydrolysis method).7 The individual molecules show a red coloration after the heating process and can then be measured by quantifying the intensity of the red tonality using a conventional spectrophotometer. This method that is used worldwide presents a number of limitations. It does not take into account the structure of the tannin pool and it also does not consider other components (anthocyanins) that can interfere in the reaction and measurement. Due to this, the tannin concentration in wine is often overestimated and it is common to observe an increase in the wine total tannin content during ageing. Nevertheless, the method also has some advantages as the ease of implementation and reliability.

Tannin measurement by precipitation

Once understood that the astringency perception is caused by the precipitation of the salivary proteins after the interaction with the tannin molecules, the following question comes into our minds: Why not using the same principle that occurs naturally in our mouth to measure tannins? Based on this reasoning two new methods for tannin analysis were recently developed. The first one relies on the interaction of tannins with an animal protein. This method uses bovine protein and is known as the bovine serum albumin protein or BSA method.8,9 The first step of the method consists of the precipitation of the tannin compounds after interaction with the BSA protein. However, a further step is required as the protein shows similar spectral properties than the tannin compounds and cannot therefore be quantified at the maximum absorption band of the tannin molecules. The reaction of the tannin complex with ferric chloride, that gives rise to blue coloured compounds, is thus measured …

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Parings for seasonal parties

The holiday times and merry seasons are filled with good food and great wine. One wine and food paring can either make or break the party that you have been planning for the last two months. To help prevent these regrettable situations, here are a few tips to help you on your way to a delicious holiday season.

Let’s first tackle the way the food interacts with the wine:

Sweetness and Umami in food both can increase the perception of bitterness, astringency, acidity and the warming effect of alcohol in wine. It can decrease the perception of body, sweetness and fruitiness in wine.

Acidity in food can decrease the perception of body, sweetness and fruitiness in wine. It increases the perception of acidity in wine – have you ever eaten a lemon with a crisp sauvignon blanc?

Salt in food can increase the perception of body in the wine and decrease the perception of bitterness, astringency and the acidity in wine. It can also enhance fruitiness and soften the tannins of the wine.

Bitterness in food will obviously enhance the perception of bitterness in wine (no dark chocolate with fresh out of the barrel Shiraz)

If you live more on the wild side and are preparing a chilli dish it’s important to note that chilli heat in food increases the perception of bitterness, astringency, acidity and the effect of alcohol in wine and it can decrease the perception of body, richness, sweetness and fruitiness in wine.

There are some high risk foods that need to be paired with specific wine styles in order to ensure that the combination is palatable.

Dishes high in sugar should be paired with a wine that has at least as much sugar as the dish.

Umami in the food will emphasise the astringency and bitterness of the tannins and thus the wine needs to have the necessary components, such as concentrated fruit flavours to be able to cope with the change in the wine. High levels of umami in the wine can be balanced by the addition of acid or salt providing this keeps with the character of the dish.

Dishes high in bitterness will emphasise the bitterness in the wine.  White wines or low-tannin reds should be considered.

Dishes with high concentration of chilli heat should be paired with white wines or low-tannin reds, each with low levels or alcohol. A wines fruitiness and sweetness can also be reduced by chilli heat so consider wines with higher levels of fruitiness and sweetness to make the effect less severe.

 

If you haven’t gotten around to designing a menu for that holiday party coming up soon here are some good ideas for meals and wine pairings. Please note that the pairing is based on wine styles rather than a specific brand. It’s very important to work from light style wines and progress to the heavier reds and finish off with a desert wine.

Starter:  An impressive, easy to make and relatively pocket friendly idea is Parma ham and melon cube skewers.

Parma ham is relatively high in fat and thus an acidic white wine would be recommended, preferably a fruit driven Sauvignon blanc or Chenin blanc should be paired with this meal in order to cut through the richness of the fat and have the tropical fruit compliment the sweet melon.

Main: A classic and all around crowd pleaser is pot roast beef prepared with an assortment of roasted vegetables.

Most recipes already contain a dry red wine; a good pairing would also be a dry red wine with a lower acid that has smooth tannins and a lower astringency.  If you are partial to a Shiraz, Cabernet sauvignon or a red blend an older vintage is recommend as the tannins would have mellowed out and the wine would have an overall smoother mouth feel as well as a beautiful spiciness that will pair well with the roast. A more pocket friendly idea would be a Merlot or a Pinotage that has been grown in a warmer region providing subtle winter spices with a beautiful fruitiness and smokiness that will pair well with the roast.

Desert: A traditional trifle containing jelly, custard, Swiss roll slices, a drizzle of brandy/sherry/fruit juice, peach slices, whipped cream on top with granadilla drizzled over for aesthetic appeal.

The trifle can be served with a natural sweet, late harvest or even noble late harvest.  It is important not to oversaturate the trifle with brandy or sherry to ensure that the fruit flavours pair well with the wine, in my opinion if a pairing is conducted, tropical fruit juice should be used instead. A honey and stone fruit driven style is recommended.

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A South African abroad

Or rather 11 South African wine students plundering through the European wine scene …

It all started in February. We received the enthusiastic whatsapp in the midst of harvest. All of us 5kgs lighter, exhausted and covered in bruises we all dreamt of a summer holiday. Pairing cheese fondues and chocolate with Chasselas in Switzerland and then progressing onto Sangrias in San Sebastian, Mojiňos in Madrid with a few wine tastings sprinkled in-between.  What more could one want?

Four months later, and after 18 hours of flying, the class arrived in Geneva for our Summer School adventure. We arrived – tired, hungry and cold ready for a European summer only to be greeted with rain. But very quickly the situation was rectified by the consumption of Chasselas. Chasselas – the Justin Bieber of Swiss wine. You either hate it or you love it. Or you hated it until it started releasing bomb singles like “Love yourself” (or in wine terms – the 1992 vintage).

And so began the daily assault on our bodies. Each day we were exposed to a plethora of Chasselas and other early ripening cultivar wines – from cheeky Gamays to sophisticated Pinot noirs. Pickled with the high acidity wines of the northern hemisphere we were then satiated with bread, cheese and cold meats to soak up the alcohol so we were ready for more tastings, cellar tours, industry-related trips and technical knowledge lectures.

The Swiss wine industry was a total game-changer – with its 1% total export it’s like the quiet kid in the class who keeps to themselves but once they open up you realise the dynamic (or biodymanic) personality inside which totally shocks everyone with their Dungeons and Dragons skills (which again, like Chasselas, you either get it or you really, really don’t).

In frenzy of drinking our way through the Swiss countryside we took a day to drive to France – to Burgundy in particular. Where we enjoyed (or didn’t enjoy…) the oxidised white  wine style of Jura, explored the underground Disney villain-esque cellars of Burgundy, and ended the day with a visit to Clos Vougeout, a massive 50,4 ha single vineyard of Pinot noir.

Our time in Switzerland came to end and we said au revoir to the green landscape, Mount Blanc and Chasselas and shouted Hola to Espaňa!

Starting at the north of Spain we experienced our first taste of true Spanish wines. From the old-world cellar which, to put it delicately did not know what cellar hygiene was, to the clean-shaven, oxidation-phobic bodega we could not have picked two more contrasting wineries to visit. The petri-dish cellar, overgrown with penicilium and other fungi even David Attenborough wouldn’t talk about, produced some distinct metallic wines (possibly as a result of the flour/blood combo still used to treat the fermentation barrels) while the Taylor Swift (young, trendy, expensive and high maintenance) cellar produced full-bodied, fruity Tempranillos which suited the South African palate like a brandy and coke on night out.

In the middle of Spain we experienced the Spanish culture, starting with tapas and sightseeing and ending (like any self-professed Stellenbosch student would) with the debauchery of the Spanish nightlife where even the chaperones Despacito-ed the night away.

Further south we started to hit the top shelf of the liquor cabinet. While some still can’t drink brandy without the bitter memories of first year’s bad decisions  the rest enjoyed learning about the similarities between the South African and Spanish brandy-making methods (with a discrete scoff and “Nah, South African’s better hey” when out of earshot of the winemaker). The sherry tasting was more successful, with a flick of his wrist and a long silver taster (which personally I think was a wand because you’ve got to be magical to pour sherry like that without spilling) the winemaker poured barrel testers for us into glasses 1m below.

We ended the trip with an excursion to the eastern coast of Spain. And what better way to end off a trip of a life-time than to be supplied with bubbly in Barcelona? The tour through the 6 storey riddling and aging cellar for one of the Cava producers rivalled the 4 storey night club in Madrid.

Finally we returned, with impressive technical knowledge, damaged livers, a higher tolerance for alcohol, international connections, a close knit group of friends and an eagerness to blow up the wine industry with our dreams of installing cranes in cellars, oxidising white wines and planting Chasselas.

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ANTON SWARTS: SENIOR WINEMAKER AT SPIER AND CAPE WINE MASTER

Q. When and where were you born ? 

Reply with generous smile “I was bred and born in the picturesque town of Paarl during the 1975 vintage on 30th January.” Then adds “The same day that Ernö Rubik applied for his patent of his “Magic Cube” which later became known as Rubik’s Cube.”

Q. Where did you study ? 

“Not a straight answer !  I studied at Elsenberg College with the Cape Technikon doing the National diploma in Agriculture focussing on Viticulture, Vegetable production and Pomology.” Then adds with a smile “I am more qualified as a viticulturist than a winemaker.  To be honest , winemaking wise I am more or less self taught with 18 years of industry experience. In 1999, I started as a general harvest hand under the watchful  eye of Chris Roux at the old Wamakersvallei Winery now Wellington Wines. Then an opportunity presented itself and moved me to their bottling and cellar facility in Epping  as the supervisor. At that stage  I knew the very basics  about winemaking and could kick myself for not paying more attention in Class ! I was immediately caught up in the whole fascination of the wine world and just wanted to know more. This led me to the Cape Wine Academy (that you started) where I began the prelim course to educate myself more about this “nectar of the Gods”. I eventually became 100th Cape Wine Master in 2017.” Then added “I must say it was the opportunities that my employers, Spier Wines, that gave me the capability of education  and the belief in me for promoting me through the years without which I could never have got to where I am today.”

Q. How long have you been with Spier ?

“18 years and counting…..I started in June 1999 as a cellar Supervisor in the bottling facility known as Cape Central  Packaging. We bottling for various customers . This became Ashwood Wines and  Winepack and was bought by Wine Corp now known as Spier. “

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

“My job requires me to source wines and blend different tiers  at different price points  so I don’t actually make wine !”

Q. So describe what you do ?

“I am one of the senior winemakers at Spier and form part of a winemaking team that functions in the Secondary Winemaking Department. I help with the procurement of wines from our outside, contracted cellars who make wines for our specific requirements and our  different labels. I relook the various components that we have sourced and begin to finalise the blends and plan to bring the bulk wines in for blending and bottling. This is a year long process and covers the whole range of wines  including specialty wines  such as Woolworths low kilojoule wines and others.”

Q. Do you have a preference for any particular variety ? 

“I couldn’t chose one variety over another ! However I do have a fancy for such diverse varieties like Pinot Noir and Shiraz that have totally different origins. I also love South African Pinotage.  I also love chenin blanc and believe it is to South Africa what Riesling is to Germany. Of course, it also makes some of our best brandies.” After some thought “I am also fascinated by Sangiovese, Nebbiolo, Touriga Nacional and Tempranillo.

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

“Not really although  Germany, Burgundy, the Mosel in particular and the Rhone .”

Q. How involved do you get in the vineyard ?

“Not much. We have a team of viticulturists who spend 24/7 looking after our precious vines.”

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

“Winning awards for your wines  is always a great achievement but what I really love about  my job is to produce wines  that people enjoy. To see the satisfaction on the faces of people enjoying our wine is the most simplistic way of understanding a great achievement.” Then adds “On top of that I guess becoming a Cape Wine Master is right up there. Being selected for Team South Africa to compete in blind tastings overseas two years in a row is also very special.”

Q. Have you developed any secrets in your winemaking ? 

“If I tell you I would have to kill you !!  However, seriously, I always try to over deliver in quality and the wine  must have body, aroma and flavour. I like my  wines to be mouth-watering.

Q. What do you consider your keys in the cellar ? 

”Patience, Accuracy and Attention to detail “

Q. How important  is modern winemaking equipment to you ? 

“At Spier moder winemaking equipment is essential. It helps us get the perfect berry into the cellar so that we can make it into perfect wine !”

Q. What advice do you have to wine drinkers ?

“To enjoy your glass of wine and not to analyse it.  Enjoyment is what wine is all about.”

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The Wonderful World of Lees

Have you ever wondered if there is any value in the lees that you accumulate during the early portions of harvest and wine processing? Have you questioned the various uses associated with wine lees?

Then you’re in luck! Consulting subscribers now have access to my recent article, Wine Lees: A Powerful Tool for Winemakers in the Learning Center that discusses the advantages and disadvantages associated with the use of wine lees during wine production. If you’re looking for a way to make your wine lees work for you, then this Article may help.

If you’re missing out on Denise Gardner Winemaking’s Learning Center, the information at the bottom of this blog post can help you get started!

Lees, or the settled portion of yeast after primary fermentation, offers several opportunities for its continued use through wine production. During good vintage years, clean lees can provide molecular components, such as nitrogen-containing compounds or polysaccharides that naturally alter the wine’s mouthfeel over time. Depending on lees contact time, the mechanism of contact, and the degree of yeast autolysis, lees can also contribute aromas or flavors to the wine that may offer changes in complexity.

Many winemakers opt to keep lees in barrels with the wines intended for longer-term aging, and if they are needed, remove the lees from those wines. A more traditional practice, bâtonnage, is a form of lees contact in which white [Chardonnay] Burgundy wines stored in barrel include routine stirring of the lees. Another great stylistic benchmark region associated with bâtonnage and lees contact is Muscadet produced from the Loire Valley (France). On Muscadet wine bottles, an additional term “sur lie” can be found to indicate this process.

 


The selection of active dry yeast for primary fermentation can have an effect on your wine lees’ chemistry post-primary fermentation. Read the The Wonderful World of Lees article to find out how! Photo of active dry yeast by: Denise M. Gardner

 

Many sparkling wine styles produced by the traditional method (i.e., Méthode Traditionelle or Méthode Champenoise) also sit on lees through a portion of its production. After the second fermentation in bottle, the lees settle to the bottom of the bottle, and remain in contact with the wine over a defined period of time. When it is time to remove the lees from the bottle, each bottle is riddled. Over time, the riddling process drops the lees into the neck of the bottle where it is disgorged and re-capped. The contact with lees through the bottle’s maturation time alters mouthfeel and sensory characteristics associated with sparkling wine.

Finally, lees can also be used as a problem-solving tool in the winery, especially for wines that have specific flaws. For example, lees additions can aid in the removal or reduction of off-odors. Their addition has been shown to help reduce hydrogen sulfide and, occasionally, volatile phenols in addition to other residual contaminants.

Keeping wine in contact with lees should not be taken lightly, as several problems can emerge if the wines are not monitored or treated properly. To find out more about lees, the ways that you can use it in the winery, and potential risks associated with lees contact time, visit the complete article, Wine Lees: A Powerful Tool for Winemakers in the Learning Center.

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Grape juice: a Microbial battle field

A sip of context: In one of our Oenology modules we are learning about the biochemical makeup of grape juice and how the yeast is built to combat the difficult environment it’s placed in and still manages to produce the glorious product of wine.

Jerry, an unsuspecting Saccharomyces cerevisiae yeast, was produced the normal way, along with all his 1×106 brothers was frozen and stored. A happy life, he was content to sit and wait until his strain was chosen to go to the cellar. Some called the cellar the Promised land, others called it the battle field. Either way Jerry knew his life would never be the same, he was no longer allowed to sit idly by; he would have to live up to his potential.

The protective bag he had once called home was cut open; a giant scoop bore down on him and a sample of his kin. They were then placed in a warm liquid, all the while enjoying the change in temperature. A strange powder was pored over them, suddenly the cells were filled with energy, Jerry thought to himself ‘this must be that energetic yeast nutrient we’ve heard about’. A larger yeast cell made his presence known: “Attention cells! You are no longer in your small protective bags anymore! You are now part of a population, we are expected to expand and grow for the next 10 days, but first a test. You will be exposed to the harshest environment you could ever imagine; Sauvignon Blanc. We are talking a pH of 2.9 and an acidity of 10.11 g/l. There will be sulphur, there will be other microbes that want to take our supplies and through all of this, if we succeed we will die anyway. This is your chance to shine, this is your purpose, are you ready!?”

Jerry was tentative, however the yeast nutrient made him feel strong; he could feel his cell membrane expanding and his size increasing. He was ready.

The first wave of Sauvignon Blanc was on its way.  Still exposed to the heat, Jerry could feel his energy increasing, he watched the skies as the Sauvignon blanc rained down on them. A couple of his brothers fell as soon as the juice touched them. Others wavered a little; however the majority of them, including Jerry, remained strong. The bigger cell was right, the conditions were harsher than imaginable, but in same environment there was plenty of nitrogen and sugar for Jerry to use.

Glucose, a beautiful six carbon chain emerged in front of Jerry, he actively transported it into his system, hoping it would form something none toxic. That was the catch 22, he had to consume it to survive, but what it produced all depended on his internal environment.  On the horizon he spotted an amino acid, it wasn’t proline so he knew he could consume it. He couldn’t believe his luck, amino acids were in high demand now that the population had expanded to a little over 1×107 and showed few signs of slowing down. Actively he consumed the amino acid; fortunately it was a branch chain amino acid; meaning it would go through transamination and oxidation to form a fatty acid, from there it would react with ethanol and become something beautiful: an ethyl ester.

Thinking about the lovely smell surrounding him, he was grateful that some of the ethanol was consumed to make it. The ethanol had been increasing at an alarming rate, so much so that the microbes he once considered competition had already died off.

A day later the population had already reached 1×108 cells. Nitrogen was in very short supply and the sugar reserves were depleting. The environment had become harsher, the sugar that once sustained them had been converted into alcohol, and the only way to get some nitrogen was to scavenge from the husk of what was once a yeast cell. Everywhere Jerry turned he saw one of his kin, trying to absorb as much sugar as possible, with the hope it would turn into a flavour compound and not something toxic.

Jerry began feeling weak; he could no longer oxidize fatty acids to expand his membrane and walls. The acid levels were high and the sugar levels were low. Glycerol made movement difficult and the ethanol levels started to get to him.

All though the environment was harsh, it smelt nice, sort of like cut grass on a summer’s day mixed with dashes of stone fruit and citrus. This is what that big cell must have been talking about, what Jerry and his clan have been working for, for all this time. Jerry started to sink to the bottom and settled in a layer of husks, although this was the end he was satisfied that he had achieved his purpose: he created a fantastic wine, and his legacy would last for months or even years to come.

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