Several types of valves are used to control cooling in the fermentation stage of industrial winemaking. The wine cooling process itself is fairly straightforward, but it may highlight how valves can function as surprisingly important ingredients in improving a variety of cooling applications. Consider a typical “wine cooler” process and learn about suggested tradeoffs and advantages involved in optimum valve selection.
The Winemaking Process on an Industrial Scale
Production in most industrial-scale wineries follows a similar pattern. Productive seasons vary according to the climate of the winemaking region involved. Let’s consider a successful winery in northern California. After the long, quiet growing season comes the crush, or processing period. In September or October, crews pick the grapes via mechanical harvester. Plucking them off the vine, this device deposits the grape into tubs on semi-trailer trucks. When full, a truck is driven onto the crush pad, where its contents are tipped into a crusher/destemmer. This perforated, rotating drum holds back the stems but allows skins and juice to gush out for transfer to the fermentation tanks, where they will have a long, productive rest.
For red wines, the inner grape material, or must, stays in the tanks with the skins. This allows the resulting wine to retain more of the skins’ color and character. (It is pressed off at the end of the fermentation period.) By contrast, the makings of white wine are separated from the skins immediately, so the wine assumes a lighter color and flavor.
Wine typically ferments for 30 to 45 days, finally transferring into barrels for aging in October or November. Wines may age for a range of time span, from 1 month to 5 years or more, depending on intended quality. Red wines especially benefit from longer stays in the barrel. Finally, the wine is bottled and shipped, for our appreciation and the winemaker’s profit.
Fermentation may only be a single step in this process, but it is a critical and chemically complex one. In the fermentation tanks, naturally occurring or added yeasts transform sugars in the grape juice into alcohol as well as into carbon dioxide, which dissipates into the air. This chemical reaction also produces a fair amount of heat, which can have a negative effect on the end product. In fact, both the speed of this process and the taste of the wine itself are significantly affected by temperature, a most important variable.
So, constant, reliable control of fermentation temperature is the critical mission of a winery’s process cooling equipment. Using the proper valve helps ensure optimum temperature control.
Cooling the Stainless Steel Tanks During Fermentation
Like winemakers everywhere, the managers at the northern California vineyard need to keep the wine at a given temperature so that fermentation proceeds as the winemaker wishes. Industry-wide, the required range typically is 71 to 77°F (22 to 25°C) for reds and 59 to 64°F (15 to 18°C) for whites.
When planning their process (the current fermentation processing equipment was installed in 2013), the winemaker chose a fairly standard design. Each of 52 stainless steel tanks has a capacity of 30,000 gallons (113,562 liters) of fermenting wine. Each tank is wrapped in a dimpled, stainless steel thermal jacket. Liquid media — propylene glycol, favored because it is nontoxic and because of its well-known heat transfer properties — flows through the jacket, cooling the tank and its contents. The glycol is then piped above the tank where it runs through a gas-powered chiller. The heat transfer fluid then flows back through the jacket again, in a repeating cycle.
A resistance temperature detector (RTD) probe on the front of each tank reports the temperature to a programmable logic controller (PLC). This opens or closes a valve to allow or prevent the flow of glycol around the jacket, thus increasing or decreasing the tank’s internal temperature.
Some wineries that desire ultimate control — those producing more expensive vintages or in larger volumes — may go further. They employ double jackets on each tank and add gas-powered heaters. This allows them to cool and heat the wine to their exact specifications.
Valves Used for Temperature Control During Wine Making
The industry has several choices of valve type for thermal regulation of fermentation.
Diaphragm Valve. The northern California winery chose a product favored by the industry for decades: a solenoid diaphragm valve. This type of valve is well known for providing reliable performance. Features of this type of valve include low electrical consumption. They are by far the most common solution found in wineries.
One possible drawback, common to every model of this valve type, is bleed-hole plugging, which is due to two factors. First, by design, a diaphragm valve’s bleed hole must be about four times smaller than its pilot hole. Second, when glycol’s temperature falls to around 32°F (0°C), it starts to solidify. The small hole and the solidifying glycol lead to bleed-hole plugging. When this occurs, a maintenance person must go out, shut down the cooling line and tap the valve with a hammer to clear the plug. In some cases, a stubborn plug necessitates dismounting and disassembling the valve and clearing the opening before reassembly and restart are possible.
Ball Valves. Some wineries, particularly the highest-volume enterprises maintaining the tank volumes of 50,000 gallons (189,270 liters) or more, have opted for ball valves rather than diaphragm valves. Ball valves are air operated, so they do not have bleed holes to open or close; thus, they eliminate the glycol plugging problem.
One drawback may be that depending upon the configuration of the ball valves, they are more expensive than typical fermentation cooler diaphragm valves. The design of a ball valve also includes integral seals. This means users must schedule maintenance approximately every 50,000 cycles to repack the seals.
Angle-Body Piston Valves. About a decade ago, valve manufacturers developed a third solution for winemaking fermentation cooling applications. Angle-body piston valves are air-operated, and allow tight shutoff in both directions. Unlike diaphragm valves, they are direct-acting, with no bleed holes to clog. Angle-body piston valves generally are more expensive than diaphragm valves by less than ball valves.
Direct-Acting Temperature Control Valves. As an alternative, one valve manufacturer developed an application-specific valve for temperature regulation systems in wine production. The solenoid temperature control valve was conceived in France in conjunction with some well-known vineyards and has subsequently been applied in North American wineries. Like ball valves and angle-body piston valves, the solenoid temperature control valve is air operated and direct acting.
The valve has proven particularly useful in wineries that employ double jackets using both coolers and heaters to achieve precise temperature control. The solenoid temperature control valve comprises two valves in one body with six ports to allow both feed and return of media. Due to its design, the same valve can control both hot and cold glycol flows.
Traditionally, vineyards have controlled double jackets using arrays of up to four diaphragm valves. However, to prevent backpressure from opening the diaphragm valves, this arrangement requires putting four check valves in front of the diaphragm valves. It also requires extensive wiring and installation work by a mechanical contractor.
By contrast, each solenoid temperature control valve can replace up to four diaphragm valves and four check valves each. It runs on a single air line. It also eliminates the familiar glycol plugging problem. As used in those vineyards requiring precise control, the solenoid temperature control valve narrows the deadband, or range wherein heating or cooling control inputs produce no effect. Thus, the winemaker can manage fermentation temperature to a fine degree, hoping to get a faster fermentation or to produce a better quality of wine.
The solenoid temperature control valve also is suitable for other cooling applications where the process requirements are less straightforward than usual. For instance, in the winery, it also can be used to control micro-oxygenation of fermenting room vats to aid stabilization, maturation and molecular mixing. This helps ensure that each batch achieves high quality and optimal taste.
Outside the winemaking industry, the solenoid temperature control valve is used for habitat cooling in the poultry industry, keeping chicken in the most comfortable temperature range to encourage maximum egg production. In fact, this specialized mixing valve might be considered in any industrial situation that demands maintenance of thermal media at two different temperatures for supply to one location.
Looking Ahead for Wine Makers
Given the motivations that underlie consumption of their product, there’s a saying in the wine industry: “When everybody else’s business is good, the wine business is good. When everybody else’s business is bad, the wine business is even better.”
The northern California winery has had excellent results from the cooling system now running its 52 fermentation vessels. Its managers are currently scheduling an expansion to add 52 more tanks. When it comes to valves for fermentation temperature control, they plan to consider their selections carefully.
Whether for winemaking or other process applications, features to seek in any valve include installation ease, decreased downtime, reduced maintenance costs and total cost of ownership, long service life and precise, reliable control.