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New World Wine Maker Blog

Social microbes and Schizosaccharomyces pombe

By Erika Szymanski of  The Winoscope

If there’s been a theme to the wine microbiology research of the past few years, it’s been microbial communities. Don’t just study one yeast or bacteria at once; look at an environment’s microbial population. And if there’s been a supporting theme, it’s been non-Saccharomyces yeast. Don’t just look at Saccharomyces cerevisiae; pay attention to at least some of the other, marginalized members of the microbial community, and ask what they can do for you.

Those two themes are obviously related. Studying microbial communities means noticing all of the auxiliary players in the environment. Noticing those players usually leads to asking what they’re doing and then to asking how you can exploit them. In another way, though, those two themes don’t overlap half often enough. Plenty of studies of non-Saccharomyces organisms keep on plodding on in the old microbiology tradition of poking and prodding at one or a few species as though they’ll work alone outside the lab.

Very forgivable in one sense. When we don’t know much about an organism in the first place, sussing out its individual characteristics before querying how it behaves in mixed company doesn’t seem unreasonable. It’s also fair to say that plenty of winemaking involves making an effort to kill all existing microbes before inoculating one selected S. cerevisiae strain that’s supposed to work alone. Then again, single-microbe studies remind me of studies of individual primates held in solitary captivity, which are not only deeply unethical but not very useful. What primate, humans included, is going to behave normally when held in solitary confinement? I’m not claiming that solitary microbe studies are unethical, or that they do harm to the microbes involved, but we have plenty of evidence that microbes are social.* Data from solitary confinement studies is limited.

So a new study on Schizosaccharomyces pombe is heading in an interesting direction, but yields data with some limitations for winemaking.

Is S. pombe a spoilage organism? That’s like asking whether dandelions are weeds: yes, in the lawns of a golf course; no, when you’re growing them for salad greens. S. pombe produces unpleasant quantities of acetic acid. It also efficiently (and even completely) metabolizes malic acid. Scott Labs sells S. pombe“teabags” that can be dropped into overly acidic tanks or barrels and then fished back out again, after malic acid has been degraded but before volatile acidity gets out of hand. New research (open-access article) has considered whether some S. pombe strains, carefully selected for low acetic acid production, might be suitable as primary fermentation organisms to be used instead of S. cerevisiae rather than afterwards. The team was able to find several low acetic-producers, able to ferment a must to dryness (albeit they tested final alcohol concentrations in the 12-12.5% range), and still able to simultaneously metabolize malic acid. Their perfunctory sensory testing, however, pretty much only judged for major faults: acidity, reduction, acceptable aroma. So when the researchers conclude that these strains might be a good option for high-acidity musts instead of malolactic fermentation, they’ve yet to account for whether that solution produces a delicious product or merely an acceptable one. Still, these strains might be incredibly useful in combination, or when a vat of something undrinkably acidic needs to be made inoffensive enough to be blended away into something else. But how do these microbes behave in company, when asked to cooperate on the job of making a drinkable wine?

I hope that this project steps forward in two directions. One: better sensory analysis. Two: what happens when S. pombe and S. cerevisiae (and perhaps some other bugs) are asked to play together.

*The Foster Lab at Oxford is up to interesting research on cooperation between microbes and other species. Here’s another (albeit dated; 2007) excellent resource on microbial sociability, from Annual Reviews in Ecology, Evolution, and Systematics. Unfortunately, it’s also behind an academic publisher’s paywall.

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Meet Carsten Miglarina – owner and winemaker of Miglarina Wines

Q. Where were you born ?

“Windhoek, Namibia in 1972.”

Q. Where did you study ?

“ I am self taught. Learning by doing!”  He continues “Although born in Namibia I grew up in South Africa and probably my interest in all things wine began at the tender age of 14 when I attempted to ferment table grapes and make wine ! I then pursued my passion for wine by entering the catering industry and was soon working as a Sommelier at restaurants that included  Le Pont La Tour in London and the Grand Roche in Paarl and then earned my winemaking stripes  as a contract winemaker in South Africa, Germany and Romania and, of course, making my own wine. My most recent winemaking adventure took me to China where I participated in the Nningxia Wine challenge.”

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

“I have developed my own style, which at times could be considered different to others and no formal training. I am different to the norm.”

Q. How involved do you get in the vineyard ? 

“I am trying to get more involved in the vineyard but as I source all my grapes and don’t own any vineyard that is not all that easy. The farms I work with are becoming more used to me and, I think, appreciate me taking an interest in the vineyard.” “Having said that all the fruit I use is hand-picked and sorted on sorting tables before crushing.”

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

“I started out with shiraz and sauvignon blanc. I still enjoy shiraz but have added Riesling, chenin blanc, chardonnay and Grenache.”

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

“Mike Dobrovic was a great influence and, of course, travelling and working in various regions, particularly Germany with their fresh, clean white wines has definitely been an influence.”

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

“Starting my own brand and growing it over the past fourteen years. To me that is really an achievement to be proud of. I started very small with a sauvignon blanc and a shiraz from Franschhoek. My first shiraz I matured in the garage of a friend ! I now have five varietal wines and export to Namibia, Reunion, Europe, Australia, USA and China and sell locally as well.”

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

With a wry smile “It would no longer be secret if I told you! However my focus is on clean, fresh fruit driven wines and I try to employ various methods to achieve this. “

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

“Even though I generally utilise the usual machinery and equipment, some modern winemaking equipment allows for interesting experimentation.” Then continues “I keep it as simple as I can in the cellar with minimum intervention and this is my basis for ensuring that my wines are fruit driven and elegant.”

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Going Ape for the Non-sulphur Grape

It’s in everything, from jam to fruit juice. Sulphur, as a simple molecule, is seriously abundant. Some people even refer to humans as sulphur-DNA based life, owing to the glue-like role it plays in keeping our DNA wound up. Its role is not arbitrary. Its highly powerful, life-giving chemical properties are also what give it it’s extreme antimicrobial abilities. It’s nuclear for yeast and bacteria; the gestapo of must, showing little mercy or discrimination.

As much as you might not want to accept it, we primates are pretty similar to fungus. We’ve both got proton pumps, ATP pumps and supercoiled DNA coding. We both love sugar, and yes, believe it or not, alcohol is toxic to us both. And so is sulphur. The same biological pathways that sulphur devastates in yeast are damaged in us too when we ingest this controversial substance. Unsurprisingly, many would agree it’s a repulsive compound, and for those of you blessed enough to have come close to the pure form – it’s certainly not a fresh ocean breeze that caresses your inner nostrils. It’s more like sandpaper spinning on the end of a drill-bit forced up your nose.

It’s no surprise people go ‘ape’ for anything lacking it. Biodynamic wines fly off the shelves locally and internationally; people hate the stuff so much they’ve convinced themselves it’s an “allergen”. Actually it’s just quite nasty.

The problem is, it’s not easy to make a non-sulphured wine. Sulphur dioxide is as ubiquitous in winemaking as the wooden barrel; more so, in fact. It serves a plethora of purposes in protecting the wine against microbes, oxygen and flavour degradation etc. Since these risks appear daily in a winery, it’s necessary to have the ultimate prevention. It’s a bit like seat belts in your car, if your car happens to be driving the Dakar Rally.

It’s not impossible though. An esteemed winemaker, or two, has said “good grapes, good winemaking”. To clarify: good grapes are healthy, non-rotten grapes – preferably with a nice low pH (a nifty natural wine protectant); and good winemaking includes cellar floors, surfaces, pumps and pipes that are clean enough to perform surgery on. After that, if it survives the first week in bottle it’ll go all the way … or so I’ve been told. And there’s plenty of examples to show.

It’s generally a bit of a dicey argument to suggest zero sulphur content in your wines. A great many wineries work hard to protect their wine and simply add the utter minimal, which acts as a failsafe more than anything to prevent flavour loss from oxygen contact. This seems to work, resulting in a severely reduced sulphur content compared to the norm. Of course, this becomes incredibly difficult when working with large quantities of wine, and not everyone has the luxury of working with healthy grapes.

It’s all, however, an unseen hypocrisy; a perversion of ‘the ignorance is bliss’ scenario. Sure, don’t spray chemicals on my lettuce, chia seeds and paleo diet. Fine, don’t ruin my weight loss, low blood pressure and increased self-esteem with sulphur. Wine has a fraction of a percentage of sulphur, please get rid of that, it’s harmful for me and my unborn baby. But…you can leave that toxic 13% alcohol in there – no problem there!

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Reviewing YAN and Hydrogen Sulfide: Part 2

By: Denise M. Gardner

In a previous post, we discussed ways in which nutrient management during primary fermentation can affect hydrogen sulfide formation and the overall “health” of the wine.  This week, we’re going to explore how to mediate hydrogen sulfide aromas and flavors in a finished wine.

Sulfur-Containing Off Aromas

In general, many wine sensory scientists and wine experts will agree that is relatively a bad habit to use the term “sulfur” to describe off-odors associated with hydrogen sulfide or “stinky” aromas that are usually described by the term “reduced.”  One of the main arguments for avoiding “sulfur” as a description term for an aroma is due to the fact that there are actually several forms of aromatic sulfur-containing compounds found in wine, and they can have very different aromas (smells, odors) associated with that one compound.  The most common groups of aromatic sulfur-containing compounds in wine are:

  • Sulfur dioxide (SO2)
  • Hydrogen sulfide (H2S)
  • Mercaptans or Thiols
  • Disulfides

Additionally, many sensory experts will advise further to avoid using the chemical names as descriptors for describing an aroma found in wine (e.g., using the term “hydrogen sulfide” to describe the hard-boiled or rotten egg aroma).  It is typically recommended to use an actual descriptor when describing an aroma (e.g., using the term “rotten eggs” when that smell exists in wine).

Sulfur Dioxide (SO2)

Sulfur dioxide is an antioxidant and antimicrobial preservative frequently used in wine production.  However, it is also produced by yeast during primary fermentation, which is why wines (and other fermented products) cannot be sulfur dioxide-free (commonly referred to as “sulfite free” in the mass media).  The aromatic descriptor commonly associated with a high concentration of sulfur dioxide is termed “burned match,” but a high concentration of sulfur dioxide can also cause a nasal irritation that many will describe as nasal burning.

Hydrogen Sulfide (H2S)

Hydrogen sulfide is an aromatic compound that is commonly described as having a “rotten egg” or “hard-boiled egg” aroma.  Like many sulfur-containing compounds, hydrogen sulfide has a low sensory threshold (<1 – 1 part per billion, ppb), indicating that about 50% of the population could sense this compound at that concentration without being able to identify it, specifically, as hydrogen sulfide.

As we saw in our previous post, hydrogen sulfide development can result as a component of poor nutrient management during primary fermentation.  Residual elemental sulfur from pesticide sprays has also been linked to latent development of hydrogen sulfide in wines.  In a 2016 edition of Appellation Cornell, Dr. Gavin Saks’ lab provided a detailed and practical report on how hydrogen sulfide can be a problem for winemakers post-bottling and the potential links to hydrogen sulfide development as a function of residual sulfur from the vineyard (Jastrzembski and Saks, 2016).

Occasionally, winemakers may also experience hydrogen sulfide formation during a sur lie aging period; a time in which the finished wine remains on the lees when lees are stirred in the wine.  It is also common for sparkling wines, produced in the traditional method, to exhibit a small perception of hydrogen sulfide when the bottle is first opened.

Mercaptans/Thiols and Disulfides

Finally, mercaptans or thiols, sulfur-containing compounds that contain the functional group –SH, and disulfides, sulfur-containing compounds that contain a S-S bond, can also be problematic for winemakers when found at high concentrations.

The presence of sulfur-containing volatile compounds is not always considered detrimental to wine quality.  For some wine grape varieties (e.g., Sauvignon Blanc), these classes of compounds can make up their varietal aroma.  In very small concentrations, sulfur-containing compounds can also be aroma enhancers, indicating that their presence can actually make the wine smell fruitier than if they were not present in the wine.  However, when at substantial concentrations, volatile sulfur-containing compounds can also produce various “stink” aromas that mask a wine’s fruitiness, freshness, and make the wine generally unappealing.  This is phenomena is dependent on the concentration of the sulfur-containing compound and the chemical makeup of the solution (i.e., wine) it is in.

Mercaptans or thiols and disulfides have a variety of descriptors associated with them, and their perception is largely based on concentration.  When we’re discussing the negatively-associated descriptors, common terms include: garlic, onion, canned asparagus, canned corn, cooked cabbage, putrefaction, burnt rubber, natural gas, and molasses amongst others.

Are There Sulfur-Containing Off-Aromas in Your Wine?

To identify if hydrogen sulfide, mercaptans/thiols, or disulfide-based off-odors exist in your wine, it may be best to use a copper screen as a bench trial.  While analytical identification of these compounds is possible, it is often expensive and leaves the winemaker guessing on what to do next.

For a quick assessment of a wine’s aroma, winemakers can drop 1-2 pre-1985 copper pennies into a glass of wine to see if the aroma freshens.  The freshening aroma is due to the fact that the copper from the penny is reacting with the sulfur-containing compounds in the wine and making them aromatically inactive.

The "penny test" is often used to quickly determine if a wine is suffering from reduction, the presence of several types sulfur-containing off-odors. Photo by: Denise M. Gardner

The “penny test” is often used to quickly determine if a wine is suffering from reduction, the presence of several types sulfur-containing off-odors. Photo by: Denise M. Gardner

A technical copper screen takes a bit more work and should be conducted in a quiet and aromatically-neutral environment.  It is recommended to do this outside of the cellar.

Copper addition, in the form of copper sulfate, is often used to remediate aromas/flavors associated with hydrogen sulfide. One-percent and 10% copper sulfate solutions can be purchased through your local wine supplier.  The basic protocol associated with a copper screen is as follows:

  1. Add 50 milliliters of wine to two glasses.
  2. Label one glass “control” and the other “copper addition” (see image below).
  3. Add 1 mL of 1% copper sulfate to the “copper addition” glass.
  4. Cap both glasses for 15 minutes.  Sniff the aroma of each wine.

Setting up a copper screen can help determine if a wine is suffering from aromas caused by sulfur-containing compounds. Photo by: Denise M. Gardner

Setting up a copper screen can help determine if a wine is suffering from aromas caused by sulfur-containing compounds. Photo by: Denise M. Gardner

Sniff (smell only!) both glasses. Most people start with the “control” and smell the treated wine (wine containing copper sulfate) second.  If the aroma/flavor of the “copper addition” glass has improved, or the hydrogen sulfide aroma has subsided, then a copper addition trial should follow to determine the exact concentration of hydrogen sulfide needed to clean up the wine in question.  Remember that the legal limit for copper allowed in a finished wine is 0.5 ppm.

Treatment of Sulfur-Containing Compound Off-Aromas

Sulfur-containing compounds are quite reactive, which can make dealing with them fairly difficult.  Many educators agree that the best way to treat sulfur-containing compounds, especially those that stink, is to prevent their existence as best as possible.

In the Appellation Cornell newsletter that focused on sulfur pesticide residues, Jastrzembski and Saks (2016) recommended that sulfur residue concentrations should not exceed 1 mg/kg at harvest in order to avoid latent hydrogen sulfide or sulfur-containing off-aromas later in processing and storage.  Additionally, many experts recommend appropriately treating fermenting musts with nutrient management strategies based on the starting YAN concentration to minimize the incidence of hydrogen sulfide formation during primary fermentation.

As described above, winemakers may also opt to treat the wine with copper sulfate to try to reduce the perception of hydrogen sulfide or other sulfur-containing aromas.  It should be noted that aromas caused by disulfides cannot be mediated with a copper sulfate addition.

There has been more conversation in the academic community regarding the reemergence of hydrogen sulfide or sulfur-containing off-aromas after a wine has been treated with copper and post-bottling.   The theory around this appears to circulate around residual copper initiating reactions in the wine that lead to more sulfur-containing off-odors.  This continues to be an ongoing discussion amongst researchers and will likely be a hot topic within with the wine industry.  For now, it is important for winemakers to understand that there may be a risk of off-odors reemerging post-copper treatment and post-bottling.  This topic will also be discussed to some degree at the 2017 PA Wine Marketing and Research Board Symposium on March 29, 2017 in State College, PA, and winemakers are encouraged to attend.

Some hydrogen sulfide or sulfur-containing off-odors can sometimes be mediated with use of fresh lees stirred in the wine or the addition yeast lees-like products.  Winemaking products like Lallemand’s Reduless, yeast hulls, or some cellulose-based products can help reduce or eliminate the intensity of these off-odors.  As with any other product additions, it is recommended that wineries always do bench trials first and before adding to the entire volume of wine.  Additionally, Enartis USA (Vinquiry) has previously distributed a fact sheet to help winemakers troubleshoot reduced wines and determine how to best treat a problem wine.

The incidence of reduction, sulfur-containing off-odors, or hydrogen sulfide can be a frustrating circumstance for winemakers.  However, adequate vineyard care and proper nutrient management during primary fermentation can help minimize the incidence rate of sulfur-containing off-odors from occurring in their wines.  Of course, problems with wines do occur, and we hope that the recommendations above will help winemakers solve wine problems pertaining to sulfur-containing off-odors.

 

Resources

Jastrzembski, J. and G. Sacks. 2016. Sulfur Residues and Post-Bottling Formation of Hydrogen Sulfide. Appellation Cornell, 3a.

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CHRISTO LE RICHE – WINEMAKER AT LE RICHE WINES

Q. Where and when were you born ?

“I was born in Belleville on 31st July 1984.”

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

“I studied at University of Stellenbosch where I achieved a BSc Agric Viticulture and Oenology followed by BSc Agric Hons Cum Laude Viticulture.”

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

“Not particularly. Winemaking is an art-form, but for me that skill lies in your ability to anticipate the quality of a vineyard, know when to pick for a specific style and how your blends will react together. Every vintage is unique and requires a unique response. This is something that comes with experience as well as knowledge and is intuitive part of winemaking that is unique to every winemaker. In terms of the production method I don’t think it is necessary to reinvent the wheel. Most of the time your “unique” technique is simply a copy of a winemaker you have no knowledge of. Winemaking is simple, but having the correct gut feel is more difficult.”

Q. How involved do you get in the vineyard ? 

A prompt reply. “As much as possible. I am the consultant to all my producers and I try and get to the vineyards at least once every two weeks during the important months of October, November, January and February. Obviously I visit the vineyards more regularly during harvest to establish the harvest date.”

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

“There is no doubt that Cabernet Sauvignon is my first love.”

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

“Andy Ericson, the Terroir Capital consultant winemaker, and Carl  Schultz stand out to me. My father (Etienne Le Riche) has also played  a major role in my development. In terms of regions I look to Napa and Bordeaux for quality inspiration, but viticulturally I look much wider. I am not a fan of one dimensional viticultural approach.”

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

“I am still way too young for the question !!  It was great to receive  a Platter 5  Star for  my 2011 Reserve Cabernet Sauvignon, but I think some of my other wines have been better. I value the friendships and connections I have made much higher than the awards.”

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

“Intuition. My “optimal ripeness” window is unique to my experience based on my travels and the vineyards I work with. That and the use of manual open top fermentation techniques.”

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

“Not very important. The equipment changes every couple of years  with a newer and better model. Once you have the equipment that works, stick to it, but be aware of what is on the market in case you need a change ! Take berry sorting equipment for example. It has been refined to optical jet selection, but I have lately been moving away from berry sorting because I believe it reduces the quality of my wines.”

Please give me a brief personal history and a look into the future.

“I was raised on Rustenberg estate on the Simonsberg, where my Dad was the winemaker and it was there my love for wine and vineyards was kindled. Working with my father  provided me with a basis to understand the industry and know what a career in winemaking  would demand from me.  After my studies I travelled  to Napa and Bordeaux to learn about Cabernet Sauvignon production, but also to enlarge my wine knowledge and life experience. I also worked for a few South African wineries which provided me with a strong base to join the family business from. After my travels I started working full time for Le Riche while furthering my studies with an Honours degree in Viticulture.

My hobbies include surfing, spearfishing, trail running  and training my dog for wing shooting. On most weekends you will find me outside in nature. The future, for me , includes finding new and better Stellenbosch vineyards to work with. It would also be great to find a few small vineyards of outstanding quality to own. I will keep perusing the Le Riche vision of producing top Stellenbosch Cabernets and striving toward finding the best expression of our vineyards.”

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Supermarket Saves

Have you ever experienced that immensely overwhelming feeling of exponential confusion when standing in the wine aisle at your local supermarket? Yeah, me too. The kaleidoscope of labels, hieroglyphic cellar and estate names, endless cultivars and blends and price ranges as wide as the Amazon River can easily have you flat on your back with TMI (too much information). To tell you the truth, there is no easy way of choosing a “good” wine from such a great variety. However, here are some of the nifty tips and tricks that I use when I’m facing the wine aisle gauntlet.

The first one is a no-brainer: specials. That is one of the best perks of buying at a supermarket. Stores regularly have specials and promotions and many times the prices can compete with those that you might find at the cellar-door. And yes, sometimes you might buy six bottles of wine where you only needed one, but its wine so who’s even counting?

Secondly, there is the all-important factor of price. For most people this is probably the variable that carries the most weight when deciding which wine to buy. And this is also very dependent on personal preference. For instance, I myself am very comfortable with drinking wines that are in the price range of R50 – R70 and I will even splurge a bit more when it is for a special occasion. I generally prefer to stay under the R100 mark when buying from a supermarket- but that’s just me.

Then of course there is the ever-confusing label. I personally do not care much for reading back labels. It has happened too many times that the back of a wine label has been completely misleading. Instead, I look for back labels that DON’T give much information on the specific bottled wine. Labels that have a story of the history of the farm or estate or even the block of vineyards the wine is made from are much more intriguing to me and does not fill my mind with expectations that are most likely not going to be met. Also, a bottle of wine with a creative front label has rarely disappointed me before. If they put as much effort into making the wine as they have into designing the label, you must be in for a treat (fingers crossed).

My next point is quite a controversial one: cork versus screw cap. This one is 100% completely up to personal preference. There is no right or wrong and the jury is still out on which one is better for the wine- if there even is a slight advantage for either. I tend to choose a screw cap when I am buying wine that I am going to take to a braai or a party at some else’s place and I choose corked red wines when I am cooking red meat for my family and close friends at home- there is nothing like the sound of a cork popping to start a wonderful evening of merriment and chatter. Whereas screw caps work better for picnics and braais (no searching for a bottle opener or a cork stopper to close the bottle back up again).

If you do have a bit of wine knowledge it will definitely count in your favour. Especially when it comes to familiar or “trustworthy” wine cellars. Most people have a favourite winery and if you particularly like one of their wines, the chances are quite good that you will like some of their other wines as well.

Another simple solution when choosing a wine: phone a friend! I have relied on wine recommendations from my friends countless times. And we all have that one friend with whom you share the exact same taste in wine. So next time you know you are heading to the wine aisle, pick their brain a little. Nobody knows your taste in wine better than your friends.

And if all else fails, do what I do- experiment. Every time I go into a supermarket to buy wine, I buy a different bottle. I make sure to try different wineries, wine styles and cultivars or blends. I see the immense variety of wines we find in supermarkets as a great privilege, instead of a daunting mass of information. In South Africa we are absolutely spoilt for choice when it comes to wines and now we don’t even have to drive to the estates to buy exclusive wines at cellar-door prices- your nearest supermarket has done the job for you.

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