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.

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!

The Mighty Midnight Crushers

It was dark, but thankfully the rain had stopped. Over a dozen hobby winemakers were waiting in the cold for the grapes. This year, it was particularly late because of a shortage of pickers, and we were several hours behind schedule.

Around 8pm, the truck rolled into the processing site. We cheered! Let the crush begin.

The Crush

The gang got to work immediately, trying to make up for lost time. We unloaded the grapes and carefully allocated about 4,000 lbs of Cabernet Sauvignon and Cabernet Franc into 50-lb totes. Organizing the allotment of grapes was challenging as lighting was inadequate and patience ran thin.

Then we ran into our first glitch - 150 lbs of Cab Sauv were missing.

Stephanie shoveling grapes

Chaos ensued. Not being able to account for the missing Cab Sauv, we decided that we could make up for the difference if we each gave up 4% of our grapes. Crisis averted. No one was going home without grapes.

An hour later, 100 lbs of grapes were found in a dark corner. A few of us tasted the grapes - definitely Cab Franc. How? Too tired to solve the mystery, we decided to re-distribute the grapes to those who were previously "taxed" 4% of the Cab Sauv. All's well that ends well.

Next, the second glitch at around 10pm - power outage.

With both crusher-destemmers running simultaneously, we must have tripped the circuit. We were crushing at a storage facility and had no access to the circuit breaker during these late hours. Our options were not looking good, and they probably included fighting raccoons over the grapes.

Thankfully, one of the winemakers lived close enough and was able to drag out his generator. Within an hour, we were back in business, crushing and de-stemming with all our might. The team remained in good spirits and were grateful that we were able to overcome each challenge. By the time we were done with the crush and clean-up, it was close to midnight.

Now, let me introduce you to our little co-op: The Mighty Midnight Crushers

The Genesis

We started planning in February. Four new hobby winemakers decided to join me to make our 2017 vintage. With only one vintage under my belt, I am hardly experienced. But thankfully, we have resources in the form of books, classes, more experienced winemakers, and access to really good grapes in Washington. More importantly, we are a group with the best attitude and eagerness to work together.

Grapes on staked vines

A month later, we placed an order for Red Mountain Cab Sauv from Artz Vineyards.

The Grapes

The first vintage I made was Yakima Valley Syrah, a forgiving varietal that is lovely even without oak. The Syrah was transformed with minimal intervention into a tasty fruit-forward wine within a year.

Cab Sauv however is a very different variety. Known for its small berry size and thick skin, Cab Sauv is favored for its tannins, which will need to be softened with oak. So I bought the smallest new French oak barrel I could find.



By end of August, the vineyards started sending out reports on the grapes. Forecasted harvest dates for different grape varieties were provided with varying degrees of accuracy, starting with white grapes followed by black and finishing with Cab Sauv and Cab Franc. The forecasted date for our Cab Sauv then was September 21.

The following month, the vineyards started running sugar (Brix) and acidity (pH and TA) tests on grape samples to determine ripeness. Still it was impossible to predict and plan our lives around the harvest date. September came and left, and Mother Nature continued to keep us guessing.

The Harvest

Our harvest date was finally set on Oct 17. We had less than a week to get ready. Two of our Mighty Midnight Crushers, Frank and Cindie, volunteered to drive to the Red Mountain AVA to collect our grapes as well as those ordered by other hobby winemakers.

Red Mountain AVA

How long the harvest may take typically depends on the weather and the availability of the pickers. Although the weather was lovely, there was a shortage of migrant workers this year. The vineyards owner herself joined her four workers to pick about 4,000 lbs of grapes that day.

It was late in the afternoon when the grapes were finally loaded onto the truck. Frank and Cindie had already been at the vineyards since that morning. They were glad to be on their way back to Western Washington. It was getting dark, and the winds were picking up. With a heavy load behind them, the drive navigating through the pass would take over three hours. They knew that they would be welcomed by over a dozen grateful winemakers waiting for the grapes in the cold. It would be dark, but hopefully the rain would have stopped.

First Crush

It was a breathtaking drive from Seattle to Snoqualmie that sun-soaked September afternoon. I was exhausted and a bit cranky, having to juggle work and taking care of a sick husband and an injured dog.

However, mother nature had chosen the harvest date, and then we were given but a few days notice to get ready for the crush. I left my invalid family members in the good hands of our house guest, packed the primary fermenter, towels, and rubber boots into the Forester, and headed out to the crush facility. My excitement grew as I approached the facility - my first crush!

Crush Day

Our Syrah grapes were picked earlier that day from Chandler Reach Vineyards, technically considered to be in the Yakima Valley, but within close proximity of the Red Mountain AVA. My partner-in-wine, Alisa, and I decided to share 100 lbs of grapes between us, which would make us about two cases of wine.

At the crush facility, the winemaking class instructor, Steve, showed us how to set up the crusher and de-stemmer. All equipment were rinsed appropriately before we proceeded. Working in a group, we gently dropped bunches of grapes into the machine, which quite efficiently removed the stems and lightly crushed the grapes into the primary fermenter. But just in case, there were two of us who manually picked out stems that were missed by the machine.

There was a certain rhythm to crushing grapes that relaxed me. It was almost therapeutic! This was the first crush for most of us, and we were eager to learn and to help. As we got the hang of it, we moved faster through the bins of grapes. Our sticky grape stains were evidence of our achievement that day.

Gently dropping grapes in

Crushed and de-stemmed

More stems manually removed

Must in primary fermenter

The freshly crushed grapes, also known as must, smelled terrific. Sulfite was added to remove any wild yeast and bacteria from the must. After crushing nearly a ton of grapes (literally) and cleaning up all the equipment, it was time to take some measurements before we took the must home.

• Brix, which measures the sugar content of the must, was at 26 degrees. It was higher than the desired range of 22-25. A higher than desired Brix might lead to high alcohol content before fermentation could complete. This could result in a stuck fermentation.
• pH, which measures acidity, was at 3.53 and was within the desired range of 3.5 and 3.8.
• Titratable acidity (TA), which measures the amount of all the combined acids in the must, was at 7.125g/L and was slightly higher than the desired 4-6g/L.

The adjustment to the must needed was thankfully simple enough. To correct the Brix without adversely impacting the pH and TA, we diluted the must with water with precise measurements that Steve provided.

Alisa, my partner-in-wine, and I with our must

Primary Fermentation

A full day after the crush, we introduced re-hydrated yeast into the must and proceeded with the twice to thrice-daily punch downs. Punching down is a process to keep the juice and the crushed grapes, particularly the skins, in contact during primary fermentation. As must ferments, the crushed grapes tend to rise to the top forming what is known as the cap. Pushing the cap down into the juice allows for flavor extraction and also prevents unwanted bacterial activities.

A pack of nutrients were added to the must two days later to feed the yeast, and a second pack was added after another two days. The must was bubbling happily and got hot (around 75 to 80 deg F) with yeast activities. Unfortunately, I never got to the desired temperature range of 80 to 90 deg F. But the house smelled like a winery during primary fermentation so I took that as a good sign!

Yeast hydrated in must and warm water

Must bubbling during fermentation

In less than a week after the crush, the Brix had dropped to 6 degrees. Twice-daily punch downs continued, and four days later, the Brix measured at -1 degree. The must was then inoculated with malolactic (ML) bacteria as we prepared for the press the next day. The ML fermentation process allowed for a controlled conversion of the tart-tasting malic acids to softer lactic acids, which would hopefully enhance the body and flavor of the wine.

Press Day

To prepare for the press, all equipment needed to be sanitized. It was not the most interesting part of winemaking but very necessary to ensure that no wild strains of yeast or bacteria would enter the juice. ML bacteria was added a day before the press so that it could benefit from being evenly distributed in the juice during the pressing process.

Sanitizing 

There were three batches of must at Steve's house that day, ready to be pressed. Steve pulled out his beautiful press from the turn of the 20th century. It belonged to his grandfather and was quite the treat!

Our must had been in primary fermentation for about ten days at that time. We poured the must into the wine press and let the juice flow into a container at the bottom of the press. This is what is known as the free run. Following that, we placed heavy blocks of wood onto the crushed grapes and exerted pressure to press the remaining juice out. The unfinished wine went into the sanitized carboys and gallon jugs, that were then air-locked.

Beautiful wine press and free run

Pouring pressed wine into carboy

The day ended with a quick sampling of the three different juices. Within only ten days, you could already taste the difference among them. Some of us (not me) had clearly done a better job with punch downs and keeping the temperature at the higher and more desired range. Those juices showed a bit more tannins and structure. My juice, which was fermented cooler and with less intervention, was more fruit-forward. I can't wait to see how our wines will continue to evolve.

My Verdict: I was a skeptic when it came to winemaking. Given the abundance of great wines available, there is hardly any need to make my own wine. However, I've been having great fun so far. I've also learned a lot about what goes on in a wine. Stay tuned for my post on secondary fermentation and bulk aging.