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Red Wine Fermentation: Cap Management

Cap management is a hot topic among winemakers, and if you know a winemaker, they

probably have a strong opinion about, well, everything. How a winemaker chooses to manage this critical part of the process depends on many factors including variety, wine style, labor availability, volume, capital, and how the winery is setup. There are relatively few methods that are commonly employed. While there have been some technologies that have come and gone over the years, this post will cover the three most common: Punchdown, Pumpover, and Pneumatage.

Cap Management has a few purposes that are equally important; to homogenize the tank, dissipate heat, wet the top of the cap to minimize unwanted microbial growth, inject oxygen, and improve extraction. Once fermentation starts, the sugar is consumed by yeast, carbon dioxide is produced, and the skins are pushed to the surface and float there.

Yeast produces not only alcohol and carbon dioxide but also heat. If the cap isn’t folded back into the fermenting liquid, the cap can act as an insulation blanket and trap so much heat that the yeast starts to die and the fermentation stops. This is known as a “stuck” fermentation and sadly, is still quite common. The hottest spot in the fermentation is at the center of the vessel, right under the cap.


Saccharomyces cerevisiae, the most common type of yeast used in the production of wine, cider, and beer, is known as a facultative anaerobe. This means that they can grow with or without oxygen, and produce energy in both aerobic and anaerobic conditions. They prefer plenty of oxygen, as it generates more ATP than fermentation does. Hence, it is important to make sure that yeast has access to the oxygen they need to build strong cell walls, increase their biomass, and conduct a healthy fermentation. Introducing air into the fermentation also helps drive polymerization reactions which help to stabilize color, build mouthfeel, and basically make all the things yummy in wine.


As the fermentation progresses, alcohol increases in concentration. Alcohol is the second most important solvent, behind water. So as fermentation progresses, the extractive rate increases. More alcohol = more extraction. So, it is vitally important to mix the skins back into the liquid so that the alcohol can help extract color and tannins. Again, all the things yummy.

The frequency that a cap is turned depends on a host of factors, such as rate/stage of fermentation, temperature, wine style, labor availability, and even the winemaker's philosophy. Over the years, I’ve noticed that winemakers range from extremely deliberate and thoughtful about things like cap management, to “eh let’s do 3 punchdowns because that’s what they do in ______ (fill in your favorite region).”


Punchdown:

In French, this is known as “Pigeage (pronounced peej-AHJE), and is the most common technique used by smaller wineries. Essentially, a person stands next to or on top of the fermentation vessel and uses a “punchdown tool” to push the skins back down into the liquid. In the past (remember that winemaking has been going on since we came out of the caves), there have been many accounts where winemakers have placed a board or plank on top of a fermenting tank, and when they punch down, have been overcome by the CO2, passed out and drowned in the tank. That’s a hangover that just won’t quit. Today, most people use smaller bins to do the fermentation, so this is less common.


After a good long day of punchdowns, there’s no need to go to the gym for a core and shoulder workout. Maybe the sweat that drips into the bin adds that elusive “salinity” that some sommeliers so laud.


There are even semi and fully automatic systems. An example of a semi-automatic system would be a heavy cart that straddles the macrobin and has an articulating pneumatic ram that pushes the skins down. Some wineries have the desire and huge budget to do this on a larger scale. They will have open-top fermenters, usually stainless steel, and a huge hydraulic ram with a large plate on the bottom; this is mounted above the tanks on a trolley system and controlled via PLC’s and sensors. While REALLY cool, also REALLY expensive.


Some winemakers like punchdowns because they are “gentle” and prevent the breakage of the skins, and give them more control over tannin extraction. While this may be true, you might get them to admit their desire for a more automated system after punching down all day in the middle of harvest.


The concern I have with punchdowns (other than the labor aspect) is oxygen integration. If you’ve ever put your nose down near an active fermentation, it’ll knock you back with CO2. I’m not convinced of the efficacy punchdowns have for adequately entraining oxygen into the fermentation.


Pumpover:

Known as “remontage” in French, this process draws liquid out from the racking valve, into some kind of pump and then up and over to the top of cap. Traditionalists often turn up their noses at pumpovers, but they might be surprised if they knew how many Uber-high-end wines are made this way.


Not all pumpover systems are created equal; the devils in the details in my opinion. Let me elaborate.


First: to screen or not to screen? Basically, this means whether or not to screen out the skins before they get to the pump. Usually, seeds don’t make their way through anyway due to their weight.


In more manual, labor-intensive cellars, the pumpover setup is shared between multiple tanks. The winemaker sets up a rolling cart outfitted with a screen, then using an elbow attached to the racking valve, allows the fermenting must to hit the screen, where the skins are separated and the wine can be sucked out of the bottom of the sump. This requires a person to stand there with a shovel and scrape the screen clean so that the skins don’t pile up and create a huge mess when the wine spills over the top of the sump. Then, once the pumpover is done, they have to lug the skins back up to the top of the tank to toss it in.


In recent years, winemakers have installed dedicated pumpover pumps on each red fermentor. Initially, many of them did not have screens installed internally in the tanks, so anything and everything would be sent through the pump. This includes skins and perhaps seeds, but also other… things. Many winemakers, if they have the option when buying tanks, are predisposing them to accept a large surface area stainless screen inside the tank. This helps mitigate the unwanted release of tannins and prevents damage to grape particles, thus reducing solids generation (less “lees”); and helps mimic the characteristics of a punchdown--- insofar as being “gentle.”


Second: mobile or dedicated pumpover system? As mentioned above, some wineries move their pumpover setup from tank to tank, mostly due to budgetary constraints. Dedicated systems are expensive.


While mobile systems might be easier on the capital expenditure front, they carry costs that are harder to quantify. For one, it takes a lot of time to move the systems to a new tank over and over again. This not only costs the winery money, but more importantly (in my opinion), limits the winemaker in being able to pumpover when they want, or NEED to. With a limited amount of time and pumpover setups, the winemaker is forced into a division of resources. There’s only so much time in a day, and the likelihood of fermentation not getting the attention it needs, when it needs it, is higher with mobile systems.


Another very important aspect I feel is often neglected, is cleanliness. When you must share a limited amount of pumpover setups, it’s inevitable that you will share something between tanks you might rather not. Cellar Transmitted Diseases, anyone? Let’s say for example, that Tank “A” had fruit in it that had a rough life… maybe a bit of rot in the vineyard, for example. Tank “B” on the other hand, has literally the best fruit on earth, blessed by Dionysus, cared for by magical vineyard elves who sang sweetly to the grapes every morning at the first crack of delicious sun. Tank “A” will likely have a higher quantity of spoilage microbes, things like Acetobacter and Brettanomyces. If you pump that tank over first and don’t do a great job cleaning the pumpover setup (or not clean at all), now our magical Tank “B” is going to have a little bit of “A” in it. The elves weep.


Third: the pump. This is an entire blog post in of itself. You can use air pumps, positive displacement pumps, flexible impeller pumps, centrifugal pumps, sinusoidal pumps, helicoidal pumps, progressive cavity pumps, piston pumps, peristaltic pumps, you name it. To avoid going down a rabbit hole that will surely interest about 1 in 4 million people, I’ll just say that they aren’t all created equal. Devils in the details.


Fourth: Oxygen, how do you get it in there? In the aforementioned case of a pumpover sump with a screen, the idea is that while that poor cellar worker is scraping skins with a shovel, air is entrained in the liquid while it’s in the sump. Problem is, the wine is off-gassing large amounts of CO2. As in the bin punchdown above, one would have a hard time breathing if they put their nose down by the pumpover sump. Many winemakers believe that little to no oxygen is getting IN.


Enter the mighty venturi. Strong, like a bull. Basically a venturi is placed inline at the top of the tank before the wine goes into the tank and distributed by the pumpover device (hopefully there is one). A venturi works by creating suction from pressure changes in the product flow and pulls in outside air. Boom. Air is entrained in the wine. No doubt about it. Years ago I spent weeks with an engineering firm, testing different pumpover setups and venturis, measuring dissolved oxygen increases, looking at spray pattern, pumping efficiency, etc. Bottom line? Venturis work. Since then, the pumpover system that was developed through this testing has been deployed all up and down the west coast.


Fifth: firehose or pumpover device? I’m not proud of it, but I’ve done the firehose method. Everyone has to an extent. If you’ve ever washed a car with a water hose, you are now qualified to pumpover a red wine fermentation via the firehose method. In practice, this looks like a cellar worker at the top of a tank riding the hose like an angry bull and spraying the top of the cap with the liquid. This technique really hasn’t evolved much over the years. It reached its peak at about the same time that the TV was invented.


One of the most important theories to understand in winemaking is the relationship between surface area and reactivity. I typically describe it by talking about iced tea. If you were to sweeten a glass of tea, which would work better: a cube of sugar or granulated? Granulated is the correct answer, not a trick question. Basically, the smaller a thing is, the more reactive it is. In the case of pumpovers, we are talking about extraction. A smaller droplet of wine, distributed evenly across the cap, will be more effective in extracting the yummy stuff from the skins. The firehose method is the cube of sugar.


Pumpover devices come in four basic types:

a rotating arm setup where the velocity of the wine hits a splashplate, causing the arm to spin and creating a “fan” of wine

a static splash plate with holes drilled in it, perhaps with some fins to help sling the wine to various parts of the tank

the “TOAD” which was invented by a guy on the central coast which uses a variable pitch 4 armed spinning centrifugal design

the “LOTUS” which is a spinning cone with a variable pitch and curved slots in the cone

Each device has various levels of efficacy and a couple of them really don’t work well at all.


Luke Holcombe

Partner, Director of Winemaking

IG: @fermforge @beardedwinewizard

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