Adaptive Bagging

by

Modern tea bagging lines are marvels of  ingenuity; compact and complex machines that perform a seemingly simply task.

By Peter Keen

Tea bag making and packaging machines are a factory assembly line configured as a compact apparatus. They carry out the complex set of meticulous and demanding functions that take a simple input, a fully processed bulk tea and, increasingly, added herbal and fruit ingredients, and turn it into a simple and convenient bag and envelope.

The simplicity of input and output obscures just how varied, tailored, flexible, adaptive, fast, accurate, safe, and innovative even tiny functions need to be. These machines are certainly not simple.

One example of the importance of a tiny function is the string that connects the tea bag and tag. The traditional thread has been made of nylon and attached to the staple that seals the bag. So simple.

But so unacceptable. Consumer pressure, branding, and regulation have all moved against the use of plastics and India’s food safety agency has banned staples, an initiative likely to be matched by the European Union. The solution is complex. First, the plastic thread has been replaced by organic cotton and biodegradable PLA (polylatic acid) made from biomass waste, such as corn starch. It is very cost-effective but poses technical and chemical challenges, affecting machine design and operation.

SoilOn thread is a more recent trademarked extension of PLA bioplastics whose structure has extended the limits on string length from 86 to 170mm. This keeps the tag out of the cup and permits it to be used in tall mugs.

As for connecting the string to the bag, air knotting is replacing stapling and mechanical sewing that require stainless steel needles. Vacuum technology sucks the thread through guidance channels and ties the knot.

 The overall result is one more contribution to what has become the imperative for tea bag production: environmental as well as product quality. The dominant trend is from plastic to bio, with the nylon (plastic) and PLA (bio) representative instances.

Tea bag production has four main assembly line operations. In each of these, there’s a wide range of options, all trending strongly to bio.

Form and fill the bag

The common feature of the three machines shown here is the large rolls of materials for the bags. Historically, these were expensive muslin and silk and the bags aptly named. The combination of major shifts in tea growing and harvesting downgraded the quality of tea that could be cheaply bagged.

That plus cost pressures shifted materials to food-grade plastics and treated paper, with often heavy chemical treatment, The mainstream shapes evolved to the rectangular pillow and two-chamber folded bag. The basic method is to feed two sheets and add the 1-3 grams of tea between them, then seal and fold the resulting bag.

Bio has moved from incremental improvements to fundamental transformation of materials, with abaca hemp, from a renewable source variety of Philippines banana tree, and newer uses of non-GMO cellulosic fibers all adding degrees of biodegradability and compostability. Really advanced materials include electrospun hydrophilic polymeric nanofibers that have antibacterial and impurity filtration properties.

The tea itself has been simplified until very recently to meet the limitations of material and shape. The key issue is how the barrier of the bag can be made porous enough for the water to interact with the tea. The flow is heavily influenced by the exposed surface area and space for the tea to unfold. Efforts to bag high-quality loose leaf tea ran up against the limitations of both material and shape. By limiting the tea ingredients to broken up fannings and dust, the basic demands of fast brewing and adequate flavor were met. The legacy is the association of tea bags with inferior quality to loose leaf.

The pyramid tea bag, a tetrahedral shape with greatly increased contact surface area, has extended the range and quality of teas that can be included. (It increasingly benefits from air knotting aesthetically as well as functionally.) Ultrasound weighing and vibrating feeding in of large leaf tea and slow-flowing heavy herbs and fruit pieces are extending lower volume specialty teas as an addition to the high volume commodity market. Tea pouches and tea socks improve the infusion rate.

One of the impacts of the material and shape constraint and extension of limitations is that there is no standard tea bag machine. Some are multifunctional and modular, allowing easy retrofit and upgrade. Others can handle a variety of, say, bag materials but be tailored to pyramids only. Speeds are critical for the mass market basic bags and range widely. Machines under $10,000 offer around 100 bags a minute output and those with an extra zero on the price tag 400 per minute. Some machines add envelope packaging and variable count boxing, with digital printing – here, again, bio pushes the limits and applies compostable inks.

The main area where plastics have become a strategic concern could hardly be seen as other than trivial detail: sealing the bag. It needs to keep its shape and stay firmly closed when exposed to hot water and steeping time. The most effective sealant has been polypropylene. It’s plastic.

The amount applied to a bag is tiny but it undermines the immense progress to producing a fully biodegradable and compostable bag. That achievement has been announced by Clipper and reinforced by a collaborative industry consortium, OSC2 (“One Step Forward to Organic, Sustainable Community” – hence OSC squared.) It is a signal of just how serious the plastics issue is for our planet. The Great Pacific patch, one of the five largest oceanic plastic junkyards, is twice the size of Texas and three times that of France.

Polypropylene won’t disappear from tea bags because of its effectiveness and integral interdependence with other components of the assembly for many firms and teas. But the machines are creating new options, heat sealing in particular. Ultrasonic sealing vibrates the bag at a frequency that creates a frictional heat that melts and then welds the two surfaces. The machines are significantly more expensive.

Next step: thread and tab, as discussed

Label and package

Many functions at the end of the tea bag assembly line are candidates for full, partial or minimal automation. Boxing bags and wrapping them is one instance. Labels, bar codes, envelopes, and dividers are others. Quality control of faulty bags, weight errors, and waste fall into this category of process-driven not necessarily automation-dependent.

“Zero waste to landfill” has become a core target here and involves a fusion of management commitment, process management, safety and certification compliance and machine support. Bigelow is one firm that has made this a sustainable economic and social success factor. Tetley’s zero waste Eaglescliffe factory is reported to produce close to 300 million bags a week, 30% of the US market. It has 60 branded bags each with its own manufacturing, packaging and quality features. Unilever’s equivalent Dubai complex, currently the world’s largest, blends teas grown in 15 countries to make 6 billion Lipton tea bags a year, 1.2 million every hour.

The main contributions of machines here is in digital printing, compostable inks and physical cutting, folding, stacking, wrapping, etc. Robots are not yet on the factory floor but are certainly peeking in the door.

All in all, tea bag making is increasing in its innovation and variety. It is a growth market, with revenues estimated to increase by more than 5% a year, driven by regional dynamics. Today, they are around $40 billion worldwide. China and India are seeing a substantial shift from loose to bagged tea.

Tea bags market share is relatively small in the US because of preferences for iced and ready to drink teas. In the UK’s declining market for basic teas, they amount to 96% of the total cup volume and 90% in Germany. In Russia, the shift to bags is marked and they now amount to 56% of sales, at premium prices. Globally, bags add up to 12%. In the equipment market, Alibaba estimates that there are 1,000-3,000 suppliers of the machines and materials reviewed here.