Many food and beverage manufacturing processes require a product to be stored in a holding tank for a few hours, days, or weeks. The purpose may be temporary storage before packaging, or longer-term storage where a reaction, such as fermenting, needs to occur before processing continues.
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While storage is an important step in food and beverage manufacturing, it can be prone to spoilage unless plant managers take precautions. Without protection, air that harbors bacteria, dust, pollen, water, oil aerosols, and vapors can enter the tank and spoil or contaminate a product.
There are three commonplace methods for avoiding product spoilage and contamination in holding tanks:
- Tank blanketing;
- Sterile air box systems; and
- Sterile air tank venting.
The costs and advantages of these solutions vary widely, so it’s important to use them in appropriate circumstances. Let’s compare their relative benefits and costs.
The most familiar solution is tank blanketing, sometimes called “padding” or “buffering.” In this method, an inert gas such as nitrogen is used to fill the empty volume of a tank, covering the product with a protective layer.
Tank blanketing is most appropriate in applications where exposure to oxygen can trigger chemical reactions that spoil products or turn them stale. A gas blanket between the product and tank ceiling maintains a stable chemical balance. Tank blanketing is often useful with combustible foods, protecting the product from oxygen, the element responsible for both spoilage and combustion reactions.
This is the most costly solution for storage protection. Producing nitrogen onsite requires a generation system—or the purchase and delivery of bottled nitrogen to your facility. In many cases, nitrogen flowing into a holding tank must also be filtered to ensure it’s pure and dry, adding costs for a filtration system, housings, and elements.
The total cost for nitrogen blanketing can be tens of thousands of dollars. While it’s a reliable option, it may not be warranted where simpler filtration is appropriate.
Sterile Air Box System
The second most common method for protecting food and beverage products in a tank is the sterile air box. This option works well in applications that require clean, bacteria-free air in and around their processes. It’s also appropriate for processors of dairy, sour, brine, or alcoholic products because it filters out contaminants while preserving the aseptic conditions favorable to aerobic fermentation.
The sterile air box does not use a separate compressor or gas cylinder, as in tank blanketing. Instead, a low-pressure blower produces enough positive pressure to keep unfiltered air out of the tank. Sterile air boxes are a full air purification solution that come equipped with blowers, pre-filtration, and a sterile air final filter. They’re available in both stationary and mobile models, which make plant modifications easier.
While less costly than most tank blanket systems, sterile air boxes are still a considerable investment. Depending on size of the application, the systems cost upwards of $20,000.
Sterile Air Tank Vent
For many applications, the most cost-efficient solution for protecting storage tanks is the sterile air tank vent. Placed at the top of the tank, this vent allows air to flow in and out, compensating for changes in volume. Inside the housing is a sterile-grade hydrophobic filter element to screen out particulates and bacteria from inflowing air.
Why not just maintain a tightly sealed tank? Because tank pressure fluctuates when products are added or emptied, or when temperatures change. It’s possible for the tank to bulge or collapse under these pressures. But if equalizing pressure is your main concern, a gas blanket or sterile air box may be overkill. A sterile air tank vent is a good alternative in plants where oxidation or fermentation are not concerns. Sterile air tank vents are especially effective where there is a high variability of inflow and outflow sterile air.
The initial purchase of a sterile air tank vent requires only the tank vent housing and a sterile-grade air filter. Costs vary depending on requirements, but the investment starts at approximately $1,000. Most sterile air tank vents are clean-in-place compatible.
If you’re a fiscally minded manager in food processing, it pays to know the spoilage risks in your holding tanks and choose storage protection scaled to those risks. The range of options includes solutions that are appropriate for your needs and budget.
Marcks is lead development engineer in Donaldson Co.’s Process Filtration Division and an actively involved member of 3-A SSI and CAGI. Reach him at firstname.lastname@example.org.