Air Sterilizer Liquid Ingredient Tank
It still seems to surprise me the number of companies in the US that have liquid sweetener tanks that do not have air sterilizer equipment in place, or perform little to no maintenance on the ones they do have. Hopefully this article will enlighten you as to their importance.
To draw down liquid from an ingredient tank, it needs to be vented. The tank must breath or a vacuum would be created and collapse the tank when drawing out the ingredient. The tank is therefore exposed to airborne contaminants, which include yeast, molds, bacteria, dirt, pollens and insects to name a few. Normally the solids levels of most sweeteners are not prone to fermentation, except in the head space of the tanks. Because most sweetener tanks are heated, condensation builds up on the top and sidewalls, diluting the solids, making it susceptible to inoculation. Mold especially loves this type of environment. Liquid sucrose, normally kept at ambient temperature, and having lower solids level, is the most prone to fermentation.
This problem of inoculation was recognized years ago. The first step was to install lamp wells in the top of the tank containing germicidal lamps. These work fine, as long as the tank level stays within 3 ft. of the lamps. Given the opportunity to look inside the tank, evidence of inoculation can be seen on the sidewalls below this level. Blowers with filters were installed to reduce contamination and condensation in the headspace. Air exhaust vents with filters were used to prevent insects from entering the tank environment and dirty air from windy days. Many of these systems are still in operation.
THE PROBLEM – The filters on this equipment are inadequate to prevent micro-organisms from entering the tank. Blower motor contaminants go freely into the liquid. The exit vents trap the moisture behind the filter and mold grows freely. Changing out the lamps exposes the tank environment to every contaminant in the air as well as potential lamp breakage, gasket material coming off the lamp well, nuts & bolts holding down the fixture, tools used to change out the fixture can fall in and anything else in the shirt pocket of the maintenance man. These inherent problems caused many concerned companies to go to the next level of sterilization.
Approximately 40 years ago the external tank sterilizer came to fruition. This unit has a electrostatic filter, a blower motor to draw air through the filter, pushing air across the germicidal lamps and then into the tank. Exhaust vents with electrostatic filters are now in place. These first air sterilizer units were made of soft metal, and were prone to rusting over time. Later, stainless steel was introduced to eliminate this additional form of contamination. These units are easier to maintain and eliminate some of the potential problems created from lamp wells.
THE PROBLEM – These units are still not efficient enough to prevent micro-organisms from entering the tanks and actually add some of their own contaminants. For germicidal lamps to be effective, they must have complete, unobstructed exposure to the air stream. Ultraviolet is only surface treatment and cannot penetrate even the smallest particles of dirt or dust. Micro-organisms can take a free ride past the U.V. exposure if riding on the back of particulate contaminants. The light chambers of these external air sterilizers contain wiring and ballast that block out some of that air flow from ultraviolet exposure. Not to mention that the wiring insulation inside the light chamber degrades under this ultraviolet and can blow into the tank. T he ballast in this chamber will rust and this contaminant will also blow into the tank. If particular care is not taken to protect the inlet to the tank during the changing of the U.V. lamps, broken glass is still a potential hazard. Filtration is a major concern, as accumulated dirt and dust build up easily in the light chamber.
The next generation of the external air sterilizer introduced the HEPA filter. At 99.97% efficiency and capturing down to .3 microns, these filters improved the capture ability substantially. Providing, of course, that the unit is properly sealed so that air flow cannot bypass the HEPA.
THE PROBLEM – In most, but not all, the HEPA is placed before the blower motor. Motor contaminants are not filtered, the lamp chamber still has the wiring and ballast, and the lack of adequate seals, will allow air to bypass the filters as they start to load up with contaminants. Dirt and dust are still evident in the lamp chamber.
The Solution – A properly designed and maintained air sterilizer will protect and keep the integrity of your primary ingredient. Changing lamps and filters are not always a solution to the problem of reducing contamination, but close inspection of the air sterilizer seals to prevent air bypass is essential. Without upgrading to the latest design in air sterilizers, little can be done with these units to catch motor contaminants, ballast rust and wire degradation. As part of the normal maintenance, replace the wiring as evidence of degradation starts to appear and wipe down the ballast and light chamber thoroughly during service. Those units with the HEPA downstream of the air flow, will capture much of this material, however the light chamber had lost much of its effectiveness due to dirt and dust accumulation. Making sure the HEPA is tightly secured to prevent bypass will increase the efficiency of the sterilizer.
The venting of the air on most of these systems is still a problem. Outside of the newest vent design, most vent filters trap moisture laden air behind them. Molds build up on the filter and vent housing, and can drip back into the tank. Changing out the filter and drying out the housing more frequently will assist in minimizing this condition. Given the pros and cons of the air sterilizer, the question comes to mind, do they create more problems than they resolve? The answer is yes to some and no to others, depending on the equipment and how well it is maintained. Poorly designed and un-maintained will create more problems with contamination than a system without. A passive system with filtered vents will only draw in the amount of air necessary to allow the tank to draw down and push the air out as it is being filled. This minimizes the amount of micro-organism entry but once they are introduced, it becomes a major issue. Condensation remains a problem as the primary breeding ground. Only the latest design in air sterilization addresses all of these issues.
To get maximum benefit from your air sterilizer, proper inspection and maintenance is essential. As a recap:
- Inspect the unit for air filtration bypass
- Replace gasket material as necessary, or install where needed
- Clean the lamp chamber of all dirt and ballast rust
- Replace U.V. Lamps every 9 months
- Replace vent filter with any sign of mold growth and clean vent housing. Check monthly
- Replace pre-filters every 6 months
- Replace HEPA annually
With the majority of systems in use, the best that can be accomplished is to minimize the problem. Wash the tank once a year and servicing the air sterilizer will help maintain the integrity of your liquid ingredient.
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