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New World Wine Maker Blog - yeast

Acid Trip Mea Culpa

Acid_Trip_by_Sergeant_Keroro-copy

The 2013 harvest is coming up in in a few weeks. Every year I start planning the next vintage as soon as the previous one is done, but as the harvest draws near the thought process gets particularly fraught. About now I make a dispassionate, unstinting assessment of what worked and what didn’t, and what I’m going to do differently this year.

Back in April I released out 2010 Estate Pinot Noir. Let me say at the outset — I LOVE this wine. It is complex, fruity, mineral, has great concentration,and is generally representative of our vineyard site and my winemaking goals. I believe that this wine has the potential for at least 20 years of positive development.

And I also believe it could have been better.

I’m absolutely certain that it is my fault that it is not.

This Pinot exhibits two characteristics that are the direct result of things I did or didn’t do in the winery, things that I made a conscious choice about. 1) The wine exhibits ethyl acetate — a very fruity, estery, slightly chemical solvent smell. We used to say “it smells like airplane dope” because model dope is mostly ethyl acetate. But almost nobody builds those kind of planes any more. Anyway, the wine has a pronounced whiff of ethyl acetate. And 2) the wine is VERY acidic.

Both of these things are there because of choices I made in the winery. The ethyl acetate is there because I chose to not inoculate the Pinot Noir with a commercial strain of Saccharomyces yeast. For years I have been allowing the Pinot fermentations to take off on indigenous yeast — the yeast present on the grapes and winery equipment. One of these indigenous yeast is Kloeckera — a fairly robust fermenter that produces ethyl acetate as a by-product of fermentation.

In past vintages, I have allowed the Kloeckera to conduct part of the ferment, and then inoculated with Saccharomyces both to ensure that all the sugar is used up in the ferment (Saccharomyces is more alcohol-tolerant than Kloeckera, and so will complete the fermentation of high-sugar musts that would challenge most Kloeckera strains) but more importantly: for the Saccharomyces to take up and metabolize the ethyl acetate produced by the indigenous Kloeckera.

The 2010 Pinot fruit came in at lower than average sugar — 23.9° Brix. The ferments blasted through, such that Kloeckera pretty much completed the fermentation before the Saccharomyces could take over—much less dominate—the yeast population in the tanks. The ethyl acetate was there, and there it stayed. I actually like it a little, but it doesn’t need to be there. And a part of me still associates ethyl acetate with some nasty-ass “natural” wines I tried back in the 70s and 80s. Lesson for 2013: Don’t allow the strain of Kloeckera I have floating around the winery to dominate the ferments.

But I have a bigger issue with the high acid level in this wine. I have posted before about the 2010 vintage. The vintage presented a number of winemaking challenges arising from the relative coolness of the season. The juices had normal to slightly above normal levels of acidity, more malic relative to tartaric than usual, unusually LOW levels of potassium, and relatively high pH. Trial tartaric adds did not drop the pH significantly, and so I made little or no acid addition to the various lots.

What surprised me with the 2010 Pinot was that very little of the total acidity fell out of solution as tartrates. The resulting wine was tart post-malolactic. And this is where I did something I have sometimes chastised consulting clients for: I let a philosophy trump practicality.

The philosophy was “hey let’s be more natural and true to the site and the vintage, and keep the number of additions to a minimum.” The practicality is that this wine probably would have tasted better if I had added a little carbonate (to precipitate some of the acidity). I never even did the trial. But here’s the reality — with all due respect to Alice Feiring, Raj Parr, Jon Bonné, Dan Berger and all the other writers and sommeliers (and winemakers) touting a lower alcohol, higher acid style of wine:

High acid wines are just not as enjoyable to drink as wines with moderate, balanced acidity.

I’m no fan of what I call “cocktail” wines: the high alcohol, high pH, high extract, high oak, high point score grape-based beverages that have dominated the attention of the wine world for the last decade. I am all for moderate alcohols, by which I mean under 15%—preferably closer to 14%. I have tasted some varieties of North Coast wines that are balanced at even lower alcohol. But I’ve been doing this long enough to remember when this pendulum swung before. I recall that the North Coast produced some really insipid wines in the late 70s and early 80s when last the industry felt it necessary to produce a more “European” style. I don’t want to go back there.

So here’s the lesson learned: Spend some time and money doing acid add forecasting. Don’t hesitate to go to the bag, for tartaric or for carbonate, as needed to get a “balanced” wine — by my definition of balance. Don’t let some dubious “philosophy” dictate what I do in the winery.

 

John Kelly is the owner and winemaker of Westwood Wines, Sonoma California. This blog was originally published on his blog: “notes from the winemaker” on the 19 August 2013

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Armageddon… don’t let it happen in your cellar! (Part 2)

Pressure

During a recent overseas trip, a colleague of mine once again lamented the joys of travelling. This trip kicked off with a baggage issue that ruined her dinner. Other jolly events included fishing her phone out of a toilet, missing a train, almost being run over by an expressionless Parisian, being kicked by a drunken teenager in Lille and finally a screaming taxi driver in Montpellier. Friendly people… the French. But the inside of a fermenting tank can also be a chaotic and even deadly place for yeast.

Modern winemaking can be very stressful and winemakers are putting increasing pressure on their minuscule friends. No, I’m serous! Pressure can indeed be a limiting factor; especially where low pH and high ethanol is concerned. Trapped carbon dioxide gas not only creates turbulence in a tank, but also contributes to a gradual increase in pressure. Pressures upward of 600 kPa (6 atm) typically stop yeast growth (think secondary fermentation of sparkling wine), but not necessarily alcoholic fermentation. In the book “Wine Science: Principles and Applications” by R.S. Jackson, it is stated that a pressure of 3000 kPa (30 atm) and upwards will completely inhibit alcoholic fermentation! What hardy fellows they are, these yeasts!

The use of pressure to control or stop yeast growth is not uncommon in German wineries, but high pressures can cause other problems. Spoilage organisms such as Lactobacillus, Torulopsis and Kloeckera are less sensitive to pressure and can cause a myriad of problems. The latter micro-organism is particularly pesky, as it is quite sulphur dioxide resistant, ferments at temperatures as low as 10°C and can produce high levels of ethyl acetate and amyl acetate.

Some beer brewers postulate that higher pressures have a positive aromatic effect on their ferments, but clear guidelines during vinification have not been established. At least there are many other ways to boost aroma, so don’t be depressed.

 

Bernard Mocke is a technical consultant for Oenobrands

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Armageddon… don’t let it happen in your cellar! (Part 1)

armageddonOn 15 February 2013, asteroid 2012 DA14 missed earth by a mere 27,700 kilometers. This ancient 130,000 ton asteroid, spanning 45 meters in diameter, would have released the same amount of energy as a detonating 2.5 megaton atomic bomb, had it collided with the earth. It looks like 15 February 2013 was global meteor day, as a 9 ton behemoth caused widespread panic and injuries as it seared through the sky above Chebarkul, a town in central Russia. Not really cataclysmic, these events, but certainly significant enough to put the thought of mass extinction into our minds.

Not only humans (and don’t forget the dinosaurs) are subject to mass extinction. Micro-organisms are intimately sensitive to changes in their environment. Take a tank of fermenting must. The savvy winemaker will manipulate this very complex environment to suit his and the fermenting yeast’s specific needs, but under certain conditions the yeast population can very quickly become extinct.

The eventual fate of the wine yeast is death. After churning out ethanol, flavour compounds and a myriad of other chemical compounds during its usually short life, the yeast unceremoniously dies. But still their job is not done. These dead cells (lees) also have a very important role, but for now the focus will be on some of the causes of death of fermenting wine yeasts.

Temperature, ethanol concentration, osmotic stress, pH, toxins, pressure, sulphur dioxide and volatile acidity can separately or in combination make your little buddies extinct. So best you follow this multi-part blog, as the next installments will focus on the specific factors listed above.

You might not be able to dodge projectiles from outer space, but you can do a lot to keep your little fermenting soldiers happy and alive right until the end.

 

Bernard Mocke is a technical consultant for Oenobrands

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Diversity

“There is a place I love in Africa, that they call the rainbow land…Chris de Burgh”

I could not help over the past few weeks to realize the challenges that entities may face as a result of diversity…diversity in just about everything, all starting with changes in  DNA. I started thinking about similarities between South African ethnic groups and what lives on grapes (forgive me, but I am pretty parochial as wine is not only my job, but also my hobby…)

South Africa as a multi-ethnic nation has diverse cultures, languages and religions. Eleven official languages are recognized in the constitution. English and Afrikaans are of European origin. Afrikaans originated mainly from Dutch ancestry and is spoken by the majority of white and Coloured South Africans. Though English is commonly used in public and commercial life, it apparently is only the fifth most-spoken home language. All ethnic and language groups have political representation in the constitutional democracy. About 80% of the South African population is of black African ancestry, divided among a variety of ethnic groups speaking different native languages, nine of which have official status. South Africa also contains the largest communities of European, Asian, and racially mixed ancestry in Africa…I bet you did not know this about our Rainbow nation.

Now I will not elaborate any further on political issues or leadership challenges, as this blog is mostly about the diversity that occurs on the republic of grapes. As winemakers, we are required not only to have a winemaking persona, but also to have personas that reflect our knowledge of chemistry, engineering, consumer behaviour, finance and many others. We are also required to know something about microbes, as they not only occur naturally on and in grapes and wine, but also direct our product in what may be acceptable for the consumer, or not. They may be friends or foes, and their diversity makes it challenging to manage, particularly if you do not know the basic elements that govern their existence…am I starting to sound like a politician?

Anyway, managing complexities efficiently probably start with understanding the magnitude of the challenge. I was utterly amazed when I took the book “Biology of Microorganisms on Grapes, in Must and in Wine”, and started counting what actually occurs on grapes and in wines. Now I am not a microbiologist, and I do not wish to quarrel about physiological differences between Leuconostoc oenos and Oenococcus oenos, but I do think even if some of these are anamorphs of each other, or genetically closely related and the differences insignificant, the diversity is quite darn amazing! The following is a table of “bugs” that occurs naturally on grapes and in fermenting wines and musts (and I did not count the sub-species…:

Bug

Genus

Species

How many species?
Lactic   acid  bacteria Lactobacillus brevis

16

buchneri
casei
fermentum
curvatus
delbrueckii
diolivorans
fructivorans
hilgardii
jensenii
kunkeei
mali
nagelli
paracasei
plantarum
vini
Leuconostoc mesenteroides

1

Oenococcus oeni

1

Pediococcus damnosus

4

inopinatus
parvulus
pentosaceus
Weissellas paramesenteroides

1

Acetic   acid- bacteria Acetobacter aceti

9

pasteurianus
peroxydans
orleaniensis
lovaniensis
estuniensis
malorum
cerevisiae
oeni
Gluconacetobacter liquefaciens

8

xylinus
hansenii
europaeus
oboediens
intermedius
entanii
johannae
Gluconobacter oxydans

1

Yeasts Hanseniaspora  

22

Metschnikowia  
Candida  
Cryptococcus  
Rhodotorula  
Aureobasidium  
Rhodosporidium  
Auriculibuller  
Brettanomyces  
Bulleromyces  
Debaromyces  
Issatchenka  
Kluyveromyces  
Lipomyces  
Pichia  
Sporidiobolus  
Sporobolomyces  
Torulaspora  
Yarrowia  
Zygoascus  
Zygosaccaharomyces  
Botrytis  
Saccharomyces cerevisiae

4

  bayanus
pastorianus
kudreavzevii
Bacteriophages

 

Isn’t this amazing? Not counting strains and sub-species, Lactobacillus has more than 22 genera and species, acetic acid bacteria more than 18, and yeasts more than 26!

And the most important thing to remember, I suppose, is to either educate yourself as a manager that guides this immense diversity (“winemaker”) in the oenological principles, or surround yourself with people who can.

Wish some leaders could learn from this…

Bertus Fourie is a winemaker, turned Enology lecturer and creator of the Barista coffee Pinotage.

 

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The (Colloidal) Matrix Part III

The Architect: You played a very dangerous game.

The Oracle: Change always is.

I was fortunate enough to visit Chateau Quinalt in St.Emilion a few years ago. Now the essence of this blog is to look at alternative ways to manage lees, and not to gossip about how and why this Chateau became a “Parker Darling”, but the truth is that their Parker ratings became quite significant. And I must say, I love everything I have tasted. I was also fortunate enough to spend a bit of time in the cellar.

This is where I saw the technique of taking healthy lees and keeping it in suspension at above 350C for a substantial amount of time with a slow mixer, and using this autolyzed broth to top up the barrels…or at least this is what they have told me! The red lights started flickering, and I immediately thought to myself: “Lees, autolysis, food for bacteria, VA and finally- spoiled wine”. So I was extremely happy to meet Michael Paetzold in the early 2000’s and the technique which they refer to as Thermoflash®. This is a heat treatment process for musts and wines, based on the principles of flash pasteurization, by subjecting the product to a specific temperature for a set period of time. The treatment is ideal for the preventive or curative management of the microbes in wines. It can be applied during different stages of the winemaking process and even on different types of wines. The difference between pasteurization and flash pasteurization is heating the wine to 60-70°C for 1 to 2 minutes, vs. heating the wine to 71.5 to 74°C for 15 to 30 seconds. This shorter period, slightly more intense treatment of the wine is effective in destroying acetic acid bacteria and lactic acid bacteria, as well as Brettanomyces, while maintaining the organoleptic qualities of the product.

The nett result? Wines that can mature healthy in contact with lees until the, let’s say “mouth feel readiness” has been achieved. I have worked with this technique the past few years with excellent results. This however is not going without saying that SO2 management remains a critical aspect in maturation management, but merely a tool with a lot of potential, in order to reach a stylistic goal.

The process of autolysis may be enhanced by the addition of glucanase enzymes. These enzymes are industrially prepared from Trichoderma fungus cultures and preferably added after fermentation. Its action takes from 7 to 10 days and must occur at a temperature equal to or greater than 10◦C. Higher doses are required in red winemaking simply because phenolic compounds partially inhibit the activity of the enzyme.

Practical advances (and significantly simpler) in the management of lees include barrel racks with wheels that facilitate rolling of barrels in order to get the lees into the suspension without opening the bung hole and having to stir the lees with a putter (battonage). The Oxo trademark is the “designer’s folly” as to how to achieve this, but exactly the same can be achieved by rolling the barrels on the parallel floor stands (if of course it’s not stacked).

Different strokes for different blokes I suppose…the essence of the blog is to say that to roll or not to roll, to flush or not to flush, changing your ways to adopt some sound lees management practices will benefit your wines.

Bertus Fourie is a winemaker, turned Enology lecturer and creator of the Barista coffee Pinotage.

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The (Colloidal) Matrix part II

Trinity: Dodge this…

Unfortunately, like most things in life I suppose, too much of a good thing can be bad…and sometimes even dangerous. Although there is a significant upside to the use of healthy, “light” lees, there can be a very destructive downside! And this of course, is what every winemaker wants to dodge…

Some of the solid particles and flakes which form part of lees may be the origin of vegetal aromas and flavors, sometimes up to a point where it almost smells a bit reduced. I have heard the term “sauerkrauty” which is actually a very good descriptor for this phenomena, as it refers to both the elements of vegetal and reductiveness. Another potential risk is the fact that our “friend” the bisulfite ion, which, to a certain degree has an anti-microbial function (although not as significant as molecular SO2), as well as some free SO2, are also bound by these solid particles. Of course in the bound form, SO2 lose most of its antimicrobial function and probably all of its anti-oxidative properties.

This of course is a time bomb, simply because we are now managing all the good microbes in parallel with the high risk ones from which we are normally “protected” as a result of the effects of SO2: Brettanomyces, Pediococcus, Lactobacillus. And – the higher the pH, the higher the risks.

Another risk related to lees contact is the development of reductive odors and metallic tastes. The release of these sulfur compounds may be the result of light lees that is very tightly compacted during wine maturation. This phenomenon is potentially even more hazardous in situations where reductive odors appeared during primary fermentation.

The release of “bitter” substances in wines, combined with reductive and “Brett like odors” is another risk associated with lees contact and is related to contamination by living yeasts such as Brettanomyces and Pichia, as well as lactic acid bacteria like Pediococcus. We are well aware of exactly where they come from: insufficiently disinfected cellar equipment, lack of optimal SO2 management, high pH’s and the release of nutrients into the wine as a result of autolysis.

And speaking of release of nutrients…living lactic acid bacteria may have the ability to metabolize different amino acids with the production of biogenic amines. Hence the importance of hygiene and optimal SO2 management!

What do I propose?

To keep it simple. Manage hygiene. Manage SO2 and pH optimally. Taste frequently. And great will be your reward.

Bertus Fourie is a winemaker, turned Enology lecturer and creator of the Barista coffee Pinotage.

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