The one-gallon plastic milk jug. If you live in the U.S. and are under 45, you have known this package your entire life. Starting in the late 60’s/early 70’s, it was the replacement to heavy, breakable, and returnable glass bottles. It is a an artifact of the dawning of the plastic age. Original plastic jugs weighed in at 120 grams or more, but technological advancements coupled with the rising price of high-density polyethylene (HDPE) resin have pushed the bottle weights down to as little as 53 grams. Any lighter and, if filled with Helium, it would float away.
Seems harmless enough, right? It’s a proven, consumer-accepted, recyclable package. All good.
But if you are filling it with a contact level filler – the incumbent technology for this container type – it could be costing your business thousands each month in giveaway.
First, a little background…
Level fillers were first designed for rigid containers like glass. Stout, heavy, and unyielding, bottles could be consistently filled to precise levels. The first plastic bottles, too, were robust enough for a person to stand on and could be filled to an exacting final weight. The seal between the valve and bottle was a flat disc, and displaced air from the bottle vented directly up a tube into the product hopper, tank, or bowl above. Once the liquid reached and blocked the vent port, the level was set. The fill level remained unchanged as the valve closed and the vent tube was withdrawn. (Actually, the level decreases a minute amount as the vent tube tip is withdrawn from the product.)
However, as bottle weights decreased, so did their structural rigidity. If you have ever seen a filling valve for a half-gallon or gallon HDPE jug, surely you have noticed a small dynamic seal that collapses and expands as the bottle engages and disengages with the fill valve. Development of this diaphragm – commonly called an expandable sealing rubber – was directly motivated as plastic jugs became lighter and less rigid. It replaced the flat sealing rubber from the glass bottle days.
Why was the expandable sealing rubber needed?
The simple mechanical principle of the level valve requires that the bottle or jug be subject to head pressure from the supply tank or filling bowl. Rigid bottles were unyielding and could withstand these internal forces with little or no deformation. However, plastic bottles behaved more like balloons, and they would expand under this pressure. If suddenly released from the valve, the bottle, relieved from about a half of pound (psi) internal pressure, would contract and product would eject from the spout. Thus, the expandable sealing rubber was developed. Its purpose was to receive and contain this displaced amount. The next bottle to contact the valve would compress the expandable, and the expandable’s contents would dispense into the fresh, empty bottle.
While the expandable sealing rubber has long been in use and is approved for use by regulators and sanitarians, it does bring with it a host of issues. For one, it requires regular replacement to work properly. At normal usage rates, within three months the expandable will have been exercised nearly 300,000 times. Structural rigidity and performance will be compromised as fatigue sets in, so replacement is suggested. Another matter is that the expandable does not lend itself to cleaning in place. It must be removed and manually cleaned in a tank or some other means. Because of this, the expandable must be reinstalled after cleaning and this exercise can be an arduous, frustrating, and time-consuming task which also can lead to contamination as the piece is handled.
Additionally, the internal walls of the expandable sealing rubber are nearly the most complex contour in the product contact path. If not adequately cleaned, contamination can become rampant from bottle to bottle or, even worse, from the bottle to the entire supply tank. Thus, affecting all bottles filled until the next cleaning cycle.
So, why is filling this bottle with a level filler costing business so much?
Well, the number of variables to accurately fill lightweight HDPE jugs are many. The time the bottle is exposed to filling bowl head pressure, level control of product in the bowl, age and condition of valve components, entrained air in the product, consistency of blown bottles, the age of the bottles, and the weight and bottle wall thickness are some of the factors influencing final weight. It is not uncommon to see a standard deviation on a lot of filled bottles exceeding 10 grams.
For example, let's assume that 10-gram standard deviation. If a producer wishes to ensure their customers (and the NIST’s Weights and Measures Division) that the volume printed on the label matches, at minimum, the volume in the jug, the producer should target a final fill weight at least 30 grams over the labeled volume. (I know we are bouncing between volume and mass units of measurement here, but it’s common in the industry to do this when the fluid density is known, with one gallon of fluid milk weighing approximately 3900 grams). Based on today's milk costs, the value of product going into the jug is somewhere near 2¢ per 30 grams. Now, 2¢ per 30 grams might not sound like much, but what if your line's production output is 10M bottles per year? Suddenly, that small-sounding amount becomes an annual loss of $200,000 per year!
Not small change anymore, is it?
Exacerbating things further is that many filling lines put out much more than 10M bottles in a year. A common model 26-valve running six days a week produces closer to 21M bottles per year. In that case, suddenly 2¢ per 30 grams becomes over $400,000 in giveaway per year!
In my opinion, adopting new filling technology and creative package development is vital to the industry. The sooner dairy processors invest and innovate in this area, the sooner and longer they can reap the rewards. The old technology is simple, but very mistakenly considered inexpensive.
From a filling technology perspective, modern jug fillers should be the electronic type, either filling by weight (load cells) or by a meter (mass or volume). These precise filling systems can bring that giveaway down to only a few grams. (At PSA/Hema, we guarantee one standard deviation to be less than 0.8 grams per kilogram.) In addition, these filling technologies improve operations and product quality by offering traceability, reduction in labor for cleaning, and non-contact, ultra-hygienic filling.
Bottles should be developed that promote a fresh look for the product, but also should allow headspace for foam to develop and settle while filling (five to six extra ounces per gallon is a good rule of thumb; the more headspace, the faster bottles can be filled). This has long been a stumbling block to changing technologies – concern over market acceptance of new package – but with an aggressively changing market and consumer type, the time for change has never been more opportune.
Thank you for reading what I think is an important article at this crucial time for the U.S. Dairy industry. I have a lot of knowledge on the available and developing technologies for fluid milk filling. If you have any questions and would like to discuss this topic further, please do not hesitate to contact me. I am happy to help.