Refrigeration is one of the alcohol industry’s unsung heroes. Though rarely discussed, it plays such a vital role in breweries, cideries, distilleries, and wineries alike.
What's the Need
When storing bottle wine for any extended period of time, it's common knowledge that it must be kept under proper conditions. Typically this is somewhere around 13° C (55° F) and 70% humidity. It makes sense that temperature is important during wine production too, so much so that conservative estimates attribute over 30% of an average winery’s electrical expense to refrigeration.
Just like winemakers, winery refrigeration systems experience their greatest workload during the vintage period.
- Fruit arrives for processing at ambient temperatures, which can range up to 35° C (95° F). It's common to want to get this juice cooled immediately to 2-10° C (35-50° F). Juice/must may be cooled prior to pressing, after pressing, or both depending on various factors: grape variety, cold settling vs. flotation vs. centrifuge, cold soaking or immediate ferment, etc.
- Fermenting juice/must is constantly producing heat during alcoholic fermentation. Fermentation temperatures for whites are typically 7-20° C (45-68° F), while reds will ferment between 20-27° C (68-80° F).
- In many wineries, the high level of activity increases the cellar's ambient temperature. Anything from equipment running overtime to simply doors being opened and closed frequently can make a big difference.
With more temperature variation depending on the stage of maturation, temperature control is still very important outside of vintage. It will require plenty of refrigeration but may also require heating.
- Wines undergoing malolactic fermentation are typically held at 20-24° C (68-75° F).
- Barrel storage rooms require constant temperatures around 13-16° C (55-60° F).
- Clarification processes such as fining, centrifuging, filtering, and clarifying may need temperatures anywhere from 0-25° C (32-77 F).
- Sparkling wine, particularly those produced using the Charmat process, requires temperatures below 12° C (54° F) to promote carbonation.
- Bottling temperature is typically kept around 15° C (60° F), helping limit dissolved oxygen while allowing accurate fill heights.
Considerations for other Alcohol Producers
Differences in production requirements create variables that must be considered when choosing refrigeration equipment. Wineries and breweries would be on opposite ends of the spectrum with cideries and distilleries somewhere in between.
Breweries operate on a shorter, more regulated cycle than wineries. The time frame from brewing to bottle is typically a month or less, and the turnover creates a continuous demand for cooling. On the other hand, breweries operate in a broader temperature range than wineries due to the process flow:
- Boiled wort must be rapidly cooled after brewing from 100° C (230° F) to 7-20 °C (45-68° F) for fermentation.
- Conditioning and bright beer tanks will generally be maintained around 5° C (40° F).
- Bottling operations will often be completed close to 0° C (32° F).
Most people consider refrigeration the process of making things cold. Since heat is a form of energy and cannot be destroyed, refrigeration is really the transfer of heat from one place to another.
Commercial refrigeration units, air conditioners, and home refrigerators are all types of mechanical refrigeration systems, which can be simplified into 4 basic components: evaporator, condenser, compressor, and metering device (also known as expansion valve). A refrigerant is cycled through, transferring heat by changing states between liquid and gas:
- The compressor receives refrigerant gas at a low pressure and temperature, then discharges it to the condenser at a high temperature and pressure.
- The condenser converts this gas into a high pressure liquid, transferring heat from the refrigerant to the outside air.
- The metering device releases this liquid from the condenser at a decreased pressure into the evaporator.
- The evaporator uses the now cool refrigerant liquid to transfer more heat back into the cycle by converting it back to a gas state.
- The gas returns from the evaporator to the compressor, and the cycle continues anew.
A typical home refrigerator keeps food cold by using this cycle to transfer heat out of air, which is returned into the refrigerator cabinet to create a cooling effect. Winery refrigeration systems typically use a coolant liquid created using propylene glycol.
Propylene glycol (PG) is considered a food-grade antifreeze. Under normal conditions, it is a colorless, nearly odorless, viscous liquid. Propylene glycol is also used to produce polyurethane and plastics, and interestingly is a common additive in food, beverage, and medicinal products (remember the Fireball Whiskey controversy?). While I’ve never put PG in a product, it’s definitely the first choice for refrigeration needs in the alcohol industry.
Most wineries use a 30-40% glycol mixture for their coolant liquid as it provides several benefits over just normal water:
- Lower freezing point between -15° and -20° C (5 and -4° F) allows for lower operating temperatures without risk of system freeze over and damage to the refrigeration unit.
- Better temperature holding minimizes heat pickup on delivery and return, particularly important for larger facilities with more extensive piping.
- Less stress on pumps due to lubricating properties.
Refrigeration unit – Unsurprisingly, this is the system’s heart and soul. It must be of sufficient size to keep up with highest load required (more on this later).
Glycol storage vessel – A well-insulated stainless steel tank is ideal as it will minimize heat gain. Logistically, the storage vessel should be in the coolest area possible while remaining near the refrigeration unit, which cycles glycol between itself and the tank. Heat is transferred out of the glycol storage vessel to maintain its set temperature.
Distribution system – This consists primarily of glycol piping and a pump, or pumps depending on demand. The pump pulls glycol from the storage vessel and cycles it through all equipment to be temperature controlled before returning it back to the storage vessel. This process transfers heat back into the glycol storage vessel. The pump(s) should have a manifold with a non-return valve that stops any flow when the pump is not operating. The piping should also be fitted with shut-off valves throughout for regulating glycol flow to specific equipment and for ease of servicing.
Jacketed tanks – Beverage storage vessels specifically designed to control contents' temperature. Glycol circulates through an external cavity, creating heat exchange through the tank wall. Stainless steel tanks are the most common in the alcohol industry. There are several categories of jacketed tanks that effect efficiency, including partially or fully jacketed tanks, which affects the amount of surface allowing heat exchange.
Heat exchanger – A broad term that refers to any equipment that transfers heat between two fluids or gases, these are very useful, if not necessary, for several processes in alcohol production.
- The most common types are tube-in-tube or plate heat exchangers, which allow cooling of product without contact to the coolant. Choosing the right heat exchanger will depend on specific facility needs. Wineries cooling red grape must for cold soaking, cideries maintaining cold temperatures for bottling, and breweries cooling boiled wort for fermentation will all use a type of heat exchanger.
- Controlling interior atmospheric temperature is essential for barrel storage, but also increases efficiency for other refrigeration processes by removing excess heat available in the facility. In lieu of a separate air conditioning system, most wineries will use an air-glycol heat exchanger built into the refrigeration system.
Electronics – Electronics are present throughout the system, but these are a bit more complicated.
- The pump(s) need to be fitted with pressure switches and a basic control box. Together, these will start and stop the pump(s) in response to the pressure inside the delivery piping. Pipe pressure is determined by the current demand of the system, or what equipment is opened to allow glycol circulation. For example, if all equipment (tanks, heat exchangers, etc.) are closed or shut off, the pressure in the piping will rise and the pump(s) will switch off.
- Automating tank temperature control requires the use of solenoid valves and temperature regulators. The regulator reads the content temperature using a probe inside the tank, and the operator sets the regulator to the desired temperature. When temperature increases, the regulator automatically opens the solenoid valve to allow glycol flow. Once temperature reaches the set temperature, the solenoid will close.
There are a lot of variables to take into consideration when planning winery refrigeration, but the most important is ensuring the system can sufficiently provide cooling for all processes. Determining exactly what you need can be tricky since no 2 facilities are the same. Consulting a refrigeration specialist is highly recommended before purchasing any equipment.
Check back soon to read the second installment, Winery Refrigeration - Installation and Maintenance.