Showing posts with label Saccharomyces cerevisiae. Show all posts
Showing posts with label Saccharomyces cerevisiae. Show all posts

Monday, January 31, 2022

No Jab? No Cab.

Yes, you heard it here first! I have officially released my 2020 Tapteil Vineyard Cabernet Sauvignon. But if you haven’t got the jab, you aren’t getting the cab. 

2020 Tapteil Vineyard Cab Sauv

2020 was the first, but unfortunately not the last, pandemic vintage. When I wrote my blog post on Pandemic Winemaking last August, harvest was impending even as the delta variant of the coronavirus raged on.

Since then, the rate of virus mutation has outpaced the speed to inject vaccines into people’s arms. There is a lot misinformation about natural immunity being more effective than vaccination. Such sentiments continue despite the rising COVID death rate among the unvaccinated, the general consensus of the medical community, and a robust history of inoculation that dates back to the 1790s.

Inoculation, as a phenomenon, is not just a human experience. In fact, virtually all commercially made and many homemade wine are inoculated and oftentimes twice if it is a red.

Inoculation in the Wine World

Yeast is what turns grape juice into wine. In winemaking, crushed or pressed grapes (known as must) are typically inoculated with a wine yeast called Saccharomyces cerevisiae or S. cerevisiae to kick start the alcoholic fermentation.

In the last few years, the “natural” wine fad has grown in popularity. The perception is that wine made with wild yeasts in the air is superior to the one made by inoculating cultured yeasts. After all, according to the argument, spontaneous fermentation of grapes was how wine was discovered in the “old days.”

Commercial S. cerevisiae 

I remembered taking a Wine History class where we had to taste a series of wines made in the “old ways.” They didn’t taste very good. In fact, Ancient Greeks mixed their wine with sea water in the ratio of four parts sea water to one part wine. In a similar fashion, the Romans diluted their wine for libation. That makes you wonder how the wine must taste back then.

If Inoculated Fermentation is Like Vaccination

S. cerevisiae is the commercially available yeast used in winemaking. The most conservative approach after harvest is to add sulfite to the must to kill off any wild yeasts and bacteria. After a couple of days when the sulfite is no longer active, the winemaker will then inoculate the must with S. cerevisiae. It is the most reliable yeast specie to complete alcoholic fermentation, which is important on two counts.

Acclimating yeast starter to must

First, virtually no sugar is left when alcoholic fermentation is complete. Sugar attracts microbial activities, which cause wine to turn into vinegar. The lack of sugar limits the potential for spoilage. Second, alcohol inhibits bacterial growth. Complete fermentation usually results in 12-14% alcohol content, which provides additional protection to the wine.

Although believed to have originated from grape skin, naturally occurring S. cerevisiae make up a minuscule fraction (0.00005% to 0.1%) of the fungal community in ripe grapes. Relying on ambient S. cerevisiae to kick off fermentation is unpredictable. So what about the other naturally occurring yeasts in the vineyard?

Then Spontaneous Fermentation is Like Natural Immunity

To count on naturally occurring yeasts in the vineyard for fermentation means that you are at the mercy of having a critical mass of the right yeast species to kick off a spontaneous fermentation. In the best case scenario, spontaneous fermentation takes off. Now you hope that whatever the wild yeast species involved in the fermentation do not give out undesirable aromas or off-flavors to the wine.

Ripening grapes

By far the biggest challenge with using naturally occurring yeasts is stuck fermentation. Most wild yeast species do not tolerate more than 6% alcohol content. This means that the yeasts die off before all the sugar is converted to alcohol. The end result is a high sugar and low alcohol wine that becomes a magnet for microbial activities and is prone to vinegarizing.

Theoretically, it is possible to start spontaneous fermentation with wild yeasts and then inoculate with S. cerevisiae to ensure the fermentation is complete to dryness (or no sugar). This requires a skilled winemaker and a well-established vineyard fungal community. In the best of both worlds, the wine gets its unique character from the wild yeasts and the longevity from the inoculated yeasts. But if you have to pick only one fermentation approach, inoculated fermentation is definitely the way to go.

Cabernet Sauvignon grapes from Tapteil

My Verdict: For me, relying solely on spontaneous fermentation to make wine is like counting only on natural immunity (or immunity by infection) for protection during the pandemic. It may work, but it sure is chancy. I’d rather take the sure bet of an inoculated fermentation to make a good quality wine and vaccines to be my best defense during the pandemic.

My Tasting Notes: No Jab? No Cab has a fruit forward bouquet of tart cherry, fig, plum jam, and brined olive. On the palate, it is jammy with concentrated tart cherry and a slight cocoa aftertaste. The wine is full-bodied with high acidity and a tiny explosion of very fine tannins. The finish lingers and is tart at the back of the mouth.

Sunday, November 26, 2017

Feeding the Beast

I am fascinated by yeast, especially the species known as Saccharomyces cerevisiae. S. cerevisiae is responsible for alcoholic fermentation and baking. These single-celled microorganisms convert carbohydrates into alcohol and carbon dioxide. The happy outcome of the process is wine or beer or a delicious slice of sourdough.

Wine yeast
Experienced and skilled winemakers in established wine countries often use native yeasts for alcoholic fermentation because the right type of yeasts have been cultivated over centuries and thrive in the environment. Hobby winemakers, like myself, who purchase grapes from fairly young vineyards, are better off using commercially produced wine yeast. This is sold dry in packets the same way you get bread yeast or in bricks for larger quantities.

But before we add wine yeast to crushed grapes (also known as the must), we have to first kill off any existing wild yeasts and microorganisms by adding sulfite. If not, these can contribute to off flavors and spoilage during the fermentation process. Two days after adding sulfite, wine yeast is then introduced to the must.

A key job of the winemaker then is to nourish the yeast so that it can complete alcoholic fermentation. Here are two things I've learned in making the 2017 vintage.

Yeast Gets Hungry  

Very much like baking sourdough, you first make a starter by activating the dry yeast in warm water that is supplemented with some nutrients. (I used Go-Ferm.) Then you feed it with sugar; in this case, a 1:1 ratio of must and water. Temperature control is important as the yeast is quite thermosensitive.
Activating yeast
Several hours later, the yeast would feast on the sugar and start to multiply. A healthy starter expands in size and bubbles happily. However, if the yeast is starving, it tells you in the most dramatic pitiful way, which was what happened to me.

Healthy starter
Starving yeast
Thankfully the fix was simple enough. I just had to add more juice to the starter, and within a half-hour, the starter came back to life. But just in case, it is good to have spare yeast and nutrients around.  

Slowly acclimatize the starter by putting the bowl on the must in the primary fermentor for a few hours before pouring it in. Soon, the primary fermentor should feel really warm, and the must should be bubbling away. If you are really quiet, you could almost hear your yeast having a blast with all the sugars in the juice. 

Sugar Alone Ain't Enough

While sugar may be delicious, it alone can't keep the yeast healthy. Other nutrients are also needed, and an important one is nitrogen. Unfortunately, Washington grapes are notorious for having a very low nitrogen level, which could inhibit yeast activity and cause a stuck fermentation. 

We did an additional measurement on the must this year, known as the Yeast Assimilable Nitrogen (YAN). True enough, our YAN reading was at 33.7 mg N/l, a far cry from the targeted 250 mg N/l. Under the guidance of more experienced winemakers, I measured the amount of nutrients that I needed to add to the must. 

Hydrometer records 0 Brix
I went with Fermaid K, which consists of a complex formulation of nitrogen, vitamins, and minerals. In addition, I threw in a small dose of diammonium phosphate (DAP) for extra nitrogen. The nutrients and supplements gave the yeast such a nice boost in the fermentation process that I reduced the second dose and didn't even bother with a third dose.

By the tenth day after harvest, the juice was fermented to dryness. Alcoholic fermentation was completed. The must was no more, and I officially had wine. 

The next step was to start malolactic fermentation on the wine, and then it was time to press. More to come on that!