Editor's Note: Glucose + yeast = alcohol + carbon dioxide – a simple formula that many people learn as early as middle school, and it's one of the most common reactions in our daily lives – it feeds us, such as bread, and also provides us with moments of pleasure, such as wine. The hero behind it: yeast, in the eyes of Liu Lin MW, is not just an invisible microorganism.
As the name suggests, yeast is the mother of ferments. She is a species of fungus, along with bacteria, degrading organic matter day and night for nature's balance, year after year. In an anaerobic state, the yeast eats sugar, squeezes out alcohol, and in the process gives the world a little calorie, and when it is full, it burps (carbon dioxide). When the oxygen is constantly flowing, people are not idle, and what is squeezed out is no longer alcohol, but water.
The wonder of nature's creation, while giving melon fructose, also allows them to bring their own yeast. Figs, which are high in sugar, are fermented on the tree if they are picked late. Free-range chickens in the French countryside, which roam around during the summer fig ripening season, often become "drunken chickens" in the cold.
Like all foods that are easy to ferment, grapes are rich in sugar. And the yeast on the grape skin is in the layer of gray ash. Its appearance is not pretty, and it often makes people think that it is dirty. There are many kinds of yeast that come with it, and not all of them are popular with winemakers. In the vast majority of cases, the yeast that winemakers want to be able to take power is the cerevisiae species of Saccharomyces (Latin for "sugarthirsty"). If other yeasts or bacteria are seized of power, the fermented liquor is at great risk of living like it hates.
If the normal fermentation process of wine is followed, some yeast species will die due to low alcohol tolerance, such as Hansenula sp. At 4% alcohol, it will die down, and Candida sp. can carry 6-9%. And S. S. who drank a lot of alcohol and was expected by all. Cerevisiae, which can tolerate 23%, is not surprising and always has the last laugh.
The S. of the Mother World cerevisiae
Image credit: LALLEMAND PLANT CARE
Another good drinker is Brettanomyces, or Brett for short. Brett may have come from vineyards or cellars themselves, and some studies suggest that oak barrels may also be one of Brett's sources. It's a very controversial yeast that tasters have mixed reviews of.
For most academics, Brett is a textbook wine fault, and it's not uncommon for Brett to be classified as "terroir" by some. Of course, the world is always more complicated than you might think: I've also heard legends in Australia and Argentina of super-famous porcoons deliberately luring Brett into the room to add to the complexity of their aromatic expression. Whether treated or not, Brett is tenacious and once in the cellar, it is extremely difficult to eradicate.
Brett's dark culinary temperament
From the three complexes she produced,
Each has a different aroma expression
...
4 – ethyphenol (4EP,4-ethylphenol):
Farm, stables, Band-Aids
4 – ethyguaiacol (4EG,4-ethyl guaiacol):
Bacon, spices, smoky taste
Isovaleric acid (isovaleric acid):
Cheese, the taste of the Wu dialect area
(i.e. hala taste, the taste of rancidity after oxidation of oils)
Smelly feet smell
The taste of 4-EG is generally considered pleasant and acceptable, while the other two are disliked by most people. Brett's threshold also varies from person to person, with different literature mentioning that tasters can detect brett's presence when concentrations of 150 μg/liter, 300 μg/liter, and 425 μg/liter. The same taster's tasting threshold for Brett in different wines will also change, which is related to other structural elements of the wine.
Château de Beaucastel in Châteauneuf-Dux-du-Pape is Brett's classic case. Jamie Goode's book Wine Science mentions a past from American wine collector Charles Collins. Charles Collins took a sample of each of the two acclaimed vintages, 1989 and 1990, hid the name of the wine, and went to the laboratory to verify the 4EP content. As a result, the 4EP content of the 1989 vintage was 897 μg/L, and in 1990 it reached 3330 μg/L, which is many times higher than the tasting tolerance mentioned above. But that didn't stop Château de Beaucastel from existing greatly.
Castle of Beaucastel
Image source: Internet
If you don't want the sword to go astray, most winemakers will intervene. A particularly effective technique is to add sulfur dioxide as soon as possible in the early stage of fermentation, when the princes cut the glue, and immediately KO a large number of poorly tolerated yeasts and bacteria to ensure that the roots are red S. Cerevisiae made a strong appearance, multiplied rapidly, and unified the rivers and lakes.
Winemakers can also choose to use commercial yeast. Although the grapes themselves have a fairly rich reserve of native yeast, winemakers still have many reasons to favor commercial cultured yeast during the winemaking process, which is equivalent to a miracle to crush other yeasts and bacteria in numbers.
Please note
Don't call native yeast "natural yeast."
Because, all yeast is natural.
Fast, accurate and stable
Commercial Yeast = Perfect?
The benefits of using commercial yeast can be summed up as: fast, accurate and stable.
When I visited the Gallo factory in the United States, I knew what "big" was. Gallo's largest white wine fermentation tank, which can store 600,000 gallons (US); The largest red wine fermentation tank can store 600 tons (Made in the United States).
Gallo's factory in Monesto, if not intuitive enough,
For example, the black strip in the middle is actually two freight trains.
Image source: Google Maps
For highly industrialized wineries, the use of commercial yeast is a must.
First, the amount of involvement is large, and the fault tolerance rate is low;
The second is the quick turnover, each brewing cycle must end quickly, freeing up space for the next pot;
Third, the taste needs to maintain the consistency of the product.
Small-scale wineries, although there is no time limit, are also likely to be stable and accurate, inclined to commercial yeast.
As for what kind of commercial yeast to choose, there are also many exquisite. Some wineries will choose yeast with low foam, so that the fermentation container can be filled with wine liquid to the greatest extent, reduce the risk of overflow during fermentation, increase the efficiency of container use, reduce unnecessary manual operation, and of course, reduce the potential loss of wine loss.
On the contrary, there are, of course, yeasts used to make "sparkling" wine
Some wineries deliberately create a certain style, using specially cultivated "terroir" yeast, such as "Meursault" style yeast, and so on. People who are struggling for blind taste need not be said to be true. Behind every "typical" is a little-known story.
For example, the banana flavor of the coco dioxide impregnation method that was once misunderstood by many people was actually a ghost of 71B yeast that was used on a large scale by some Beaujolais Nouveau manufacturers; now with the change of trend, big manufacturers have begun to use yeast that emphasizes red fruit. Another "typical" example is Anchor's Vin 7 yeast, which induces a lot of "kiwifruit" aromas for Sauvignon Blanc .
George Duboeuf winery, which is very important to the Bo Ruolai trend
Image credit: George Duboeuf
Other wineries tend to use "neutral" yeast without inducing overly exaggerated aroma structures, such as many Champagne and Riesling manufacturers. Yu is not one by one. In recent years, low alcohol conversion rates have also been known as the subject of research in the yeast community.
Although the advantages of commercial yeast are numerous, the disadvantages are also very obvious. The biggest sin is the lack of complexity in aroma and taste. I once asked a researcher at a yeast company how many strains each product typically has in the commercial yeast for wine sold on the market. The answer is: Whether it is S or not. Cerevisiae, usually a product is a strain, there may also be 2-3 mixed together, play a different effect. He had heard of a maximum of 7 STRAINs, but this was very rare.
Click on for a clear and larger view
Image source: Screenshot from the official website of yeast company Lallemand
If you see that everyone here is not clear, let's change the angle. Dr. Matthew Goddard, a professor at Lincoln University, once did a test in which he isolated 88 S. from 4 oak barrels. Cerevisiae strain. Another study (2015) by him and colleague Sarah Knight successfully isolated 3,900 S. s. from nature (forests, vineyards, and spontaneously fermented S. Blanc in Six Major New Zealand appellations). cerevisiae yeast (six major appellations Hawke's Bay, Martinborough, Nelson, Wairau Valley, Awatere Valley and Central Otago).
Dr. Matthew Goddard
Image source: researchgate.net
If you make your own bread, you will know that the self-kept yeast sold in those historic bakeries is really heavenly in terms of flavor complexity compared to the commercial yeast in the supermarket.
So, in order to defend the uniqueness and complexity of the flavor, there are many brewers who choose native yeast. In order to ensure the smooth progress of fermentation, they may also use sulfur dioxide to clear obstacles, or make a "primer" on a small scale in advance, called pied de cuve in the French, with a small number of grapes to start fermentation first, and then wait for the large army to gather, and then directly join the advance team.
Gaja, an Italian barbaresco that uses native yeast
Image credit: Gaja
Generally speaking, the winemaking containers and workshops of the old wine cellar are full of microorganisms accumulated over the years, including yeast, so experienced winemakers only need to make slight adjustments according to the specific conditions of the year, and there is not much risk.
Of course, particularly rigorous and more serious scientists will also remind you to pay attention: if his grandparents and fathers use commercial yeast, and they claim to use native yeast, then which mother is born of this offspring?
Text | Liu Lin MW
| Liang Tongzheng
The image comes from the Internet