Talk Fermentation Like a Wine Pro

A few weekends ago, my girlfriends and I went wine tasting in a touristy town outside of Seattle. As I was going over the tech sheet, the description of a wine piqued my interest. According to the write-up, this wine was fermented with two different yeast strains. Curious, I asked the tasting room manager for more information.

Wine tasting

“Well, I am not a winemaker,” he prefaced and then proceeded to describe what essentially was a case of stuck fermentation.

If you get the sense that the term “stuck fermentation” sounds more dire than what is presented in the tech sheet, you are right! For this month’s post, we will go over some wine fermentation terms so that you can talk like a wine pro in a tasting room.

Alcoholic Fermentation

All wines go through alcoholic fermentation. This is often referred to as primary fermentation. Wine grapes are typically harvested at a sugar level of 20-25 Brix. During alcoholic fermentation, yeast converts the sugar into alcohol and carbon dioxide. To make a dry (as opposed to a sweet) wine, the fermentation will typically go for 2-3 weeks till the sugar level drops to 0 Brix. At which point, the yeast will run out of sugar to consume and become dormant. With a starting Brix of 20-25, the resulting wine will be at 11.5-15% of alcohol by volume (ABV).

Spontaneous vs. Inoculated Fermentation

Spontaneous fermentation is how wine and other fermented goodness were discovered. It refers to the fermentation caused by ambient or natural yeasts. However, not all yeast strains are capable of fermenting to dryness. Nor do they always produce the flavors you want in a wine. Except for very established wine regions where the natural yeast strains have proven success in fermenting and making good wine, one would be relying on chance to make wine using spontaneous fermentation.

Pitching yeast in inoculated fermentation

With modern winemaking, yeast strains have been commercially cultivated to reliably ferment and to produce certain characteristics in wine. In inoculated fermentation, wineries will first treat the must (fancy term for crushed grapes or juice to be fermented) with sulfite to prevent spoilage from wild yeasts and bacteria. After a couple of days, the selected yeast strain will then be pitched into the must to start the fermentation process. 

Stuck Fermentation

Sometimes alcoholic fermentation gets sluggish over time. A fermentation is considered stuck when Brix is stagnant for over 48 hours. Stuck fermentation is a symptom of stressed yeast and is a winemaker’s nightmare. Some of the stressors include:

• Inadequate yeast nutrition - Beside sugar, yeast needs nutrients to properly propagate and complete the fermentation process. There are established nutrition protocols for different yeast strains to ensure successful fermentation.
• Hostile must temperature - If the must is too cool, the yeast will become dormant, and fermentation will halt. On the converse, an excessively hot must may kill the yeast. Keeping the must at 75-85 degrees Fahrenheit is a safe guardrail.
• High alcohol must - This is often the result of fermenting grapes with a high starting Brix. The must then reaches an alcohol level that is toxic to the yeast before all the sugars are fermented. Hence, the Brix level stays stagnant and does not fall to 0.

Measuring Brix using a hydrometer

The fix for stuck fermentation is to restart it. This can be tricky and often requires a different yeast strain that can tolerate the specific must environment presented by the stuck fermentation. The resulting wine is often of a lower quality or exhibits less desirable characteristics than intended.

Primary vs. Second vs. Secondary Fermentation

This is a surprisingly confusing topic, and I have seen the terms used differently. But this is how I understand the difference:

• Primary fermentation refers to fermentation prior to racking. Racking is the process of transferring wine from one vessel to another to remove sediments and dead yeasts. Some winemakers rack in the middle of alcoholic fermentation while others do it after.

• Second fermentation refers to a new alcoholic fermentation due to the presence of sugar. This may be accidental if there is sugar left from a prior fermentation. Or it may be intentional where more yeast and sugar are added to a still wine to trigger a second fermentation and subsequent carbonation. That is how a sparkling wine is made.

• Secondary fermentation refers to fermentation after racking. If racking occurs in the middle of alcoholic fermentation, then secondary fermentation is the continuation of that. If racking occurs after alcoholic fermentation is complete, then secondary fermentation may refer to malolactic fermentation if used.

Racking from barrel to carboy

Malolactic Fermentation

Often known as malo or MLF, malolactic fermentation is the process of converting tart malic acid (think green apple) in wine to creamy lactic acid (think milk) using a bacteria called Oenococcus oeni. MLF is common in making red wine to create a velvety round texture. It is rarely used in making white wine except to create a buttery Chardonnay. MLF is sometimes known as secondary fermentation.

That concludes the primer on fermentation terms. Go forth into that tasting room and talk fermentation like a pro. Or at least spot a marketing spin. Now you know.

Winemaking Spooky Moments

Pumpkins and corn, grapes and vines. The final days of harvest are upon us!

Is it any surprise that Halloween and winemaking happen around the same time of the year? This Halloween, it seems apt that I should share three spooky moments of winemaking and the tricks to get out of them.

Halloween and winemaking

Spooky Moment #1: Starving Yeast

Two years ago, I was working on my second vintage. While my first vintage was part of a class, this was the first time I made wine with the training wheels off. I was in charge of the yeast, nutrients, and chemicals to ensure good sanitation and health for the fermentation process.

Healthy starter

It had been a year since I had prepared a yeast starter. (The downside of a once-a-year hobby.) I activated the yeast with warm water and nutrients, paying close attention to temperature control. To the hydrated yeast, I then added crushed grapes (known as the "must" in winemaker speak) diluted with an equal amount of water. The idea was to whet the appetite of the activated yeast several hours before introducing it to the eventual feast of grape-y sugary goodness.

While I thought I had kept good notes from my first vintage, it became clear that I missed some details. Important details. Like how how much must mixture I should add to the starter.

Starving yeast

I returned home from my day job to find the sad state that was my yeast starter. Instead of being round and full with tiny air bubbles, the starter was straggly and almost lifeless. Clearly I did not add enough must mixture. The yeast did not get enough sugar and was starving.

The Trick: Thankfully, it was early in the fermentation process, literally two days after harvest and crush, and this was highly recoverable. As long as there were some bubbles going on in the starter, adding more must mixture should revive the yeast in less than an hour. That was what I did and it worked. Failing which, I would have to get a new yeast starter. I added to my notes: 1 cup of must and 1 cup of water per 5 grams of yeast.

Spooky Moment #2: Rotten Eggs

Why does my must smell like rotten eggs?

H2S compound

You learn about this in class, and you are told not to panic. Still you pray it doesn't happen to you. But if you have been making wine for a while, it is inevitable.

What contributes to the rotten eggs smell is the compound hydrogen sulfide (H2S). By the time you can smell it, it typically means the yeast is stressed. The cause could be inadequate nitrogen, excessive sulfur, and/or lack of oxygen. And I believe we might have hit the jackpot on the trifecta.

• Nitrogen - Washington grapes are infamous for having a low nitrogen level. This year's particular crop had less than a third of the healthy amount of Yeast Assimilable Nitrogen (150 mg/L) for fermentation.

• Sulfur - While I had treated the must with the same amount of sulfur every year to inoculate the grapes from wild yeasts. It is possible that the vineyard had also added sulfur to preserve the fruit for the four-hour ride back to Seattle, resulting in a double dose.

• Oxygen - With the two factors above, weak air circulation and low oxygen contact with the yeast could just seal the deal for H2S production.

The Trick: First, we increased aeration with more rigorous and frequent punchdowns. We even removed the lid on the primary fermenter for several hours to improve circulation and let excess sulfur dissipate. Finally, we moved up the nutrients schedule by a day and beefed up the yeast with diammonium phosphate (DAP) to compensate for the low nitrogen level. That seemed to get the yeast going. By the next day, the rotten eggs smell was gone. Phew!

Spooky Moment #3: Sluggish Fermentation

While we fixed the H2S problem and kept fermentation going for the next few days, the drop in Brix started to slow down again at 11 degrees. (Our goal is to get to -1 or -2, which indicates that fermentation has completed.) Brix measures the sugar content in the must. Yeast coverts sugar into alcohol during fermentation. The slowdown indicates that the yeast might be experiencing stress again and might not be able to complete fermentation.

Hyrdometer to measure Brix

Sluggish or stuck fermentation is problematic. The unfermented sugar could attract bacteria. Additionally, there would not be enough carbon dioxide, a byproduct of fermentation, to provide a protective layer against oxidation. In both cases, the wine would be prone to spoilage.

The Trick: Depending on where you are in your fermentation process (high Brix or low Brix) and your winemaking skills, there are different ways to fix a sluggish or stuck fermentation. Given that we were nine days into primary fermentation and had only reached midpoint in the Brix, our best bet was to re-pitch with another yeast strain, Premier Cuvee, that is known for a fast and clean fermentation. (We normally use Premier Rouge for primary fermentation of red wine.) That was what we did, and we did manage to get the fermentation going through dryness in the next four days.

An added bonus of this second pitch of yeast is that we happened to catch the yeast starter on video, which was pretty neat!

 

My Verdict: While this is my fourth vintage, I find that I am constantly facing new challenges in winemaking and learning new things. Sure, these are spooky moments. But once you learn the tricks to overcome each challenge, you get a deeper appreciation of the process and you are rewarded with the ultimate treat! So move aside, Halloween, with your trick or treat. This is Hallowine time!