On Frankfurt bridges, take-away packaging should be mainly glass or stainless steel

The take-away system of the Frankfurt Bridges makes the use of reusable food containers as easy and convenient as that of disposable containers. On the Frankfurt Bridges, for example, every gastronomy establishment is required to provide reusable take-away packaging made of sturdy lightweight glass or enameled thin stainless steel in return for a deposit. The emptied containers can be returned to one of the 300 collection roundels on the bridges. The deposit is immediately refunded, the containers industrially cleaned and delivered back to the catering industry.

Content: A sustainable reusable system for take-away containers on the Frankfurt Bridges is described

Instead of plastic, the extremely durable and thus very long reusable materials „sturdy special glass“ and stainless steel are proposed.

For both materials, the focus is on lightweight solutions, and in the case of glass, there is the added consideration that it must not break easily.

All restaurants on the bridges are required to sell their food and beverages in a wide but fixed range of container designs. Consumers can return these containers at any time to various locations on the bridges - from there they are collected, cleaned and made available to the restaurants again.

An end to disposable plastic packaging: on the bridges, there are only reusable systems for take-away gastronomy

Takeaway gastronomy is becoming increasingly important. The food is usually sold in disposable packaging. The result: a mountain of waste. The fact that everyone brings their own container is a positive approach, but it only works with precise advance planning or when containers are carried along prophylactical - accordingly, it is rarely practiced: Most of the time you grab a coffee at Starbucks spontaneously without having your own cup with you – and once you finished drinking it, you don‘t want to carry the dirty cup with you when you continue to move through the city.

A packaging system therefore must be uncomplicated and at the same time environmentally friendly and resource-saving. This means:

(1) It must be possible to take the packaging with the food on site when buying it, and then get rid of it again without complications: Availability of packaging when buying the food must be as simple as disposing of packaging once you are finished, because only then will people accept it.

(2) The material of the packaging must be reusable. This can only work if the economies of scale in return/collection, cleaning and redistribution to the catering industry are realized through a limited number of packaging forms.

Shirin Kriklava - Stiftung Altes Neuland Frankfurt

Only if the complexity of take-away packaging is reduced and all restaurants use the same range of containers can the necessary economies of scale be achieved

Similar to the way different beverages -from sparkling water to lemonade to spritzer- are being bottled by different suppliers successfully and efficiently using one and the same type „bead bottles“, a standardization of the container range can also serve to establish an environmentally friendly reusable system in the take-away sector: Consumers can get rid of take-away containers anywhere in the neighborhood at collection points; this way, the containers do not have to be returned to the exact vendor they came from, but can be collected in bundles for all restaurateurs in the neighborhood, cleaned, and redistributed according to the needs of the individual establishment. If each restaurant and café had its own specific bin designs, this would not be possible – at least not with the necessary economies of scale.

Helene Holunder, Lieblingsglas.de, Küchengötter.de, t-online

The Frankfurt Bridges takeaway system operates without plastic containers

There are already some reusable systems for the catering industry, but often the tableware here is still made of plastic.

And reusable plastic tableware has one major disadvantage: scratches and discoloration make it look unhygienic and unappetizing after a while, so it will have to be replaced at some point. Therefore, even plastic tableware that can be reused up to two or three hundred times eventually ends up in the trash and needs to be replaced.

Since reusable plastic that can be used as a container for hot or acidic food must have certain properties, it is currently not recyclable. In addition, people often intuitively or subjectively dislike consuming hot or acidic food and beverages from plastic containers.

The aim at the Frankfurt Bridges is therefore to use only packaging that

is produced with the lowest possible energy input,
can be reused as often as possible, and
is lightweight and unbreakable. In addition, there are two further essential aspects:
the containers must look appealing and
intuitively, hot and sour foods and beverages should also be gladly consumed from them.

A look into the past helps to find solutions.

Experts on the Topic

Deutsches Verpackungsinstitut - Fraunhofer-Institut für Verfahrenstechnik und Verpackungen IVV - TU Dortmund Lehrstuhl für Förder- und Lagerwesen Verpackungstechnik - TH Nürnberg Umwelt und Rohstoffe

The first reusable solution: enameled metal take-away containers

People have been transporting ready-made food for centuries, but only the past few decades have they been doing so in plastic. So what did they use before that? Among other things: containers made of metal, such as the „Henkelmann“. The metal containers are sturdy and durable and, because they are equipped with compartments, very practical.

If they do become unusable, the material can be recycled and used to make new containers.

However, metal has a disadvantage: eating from it with metal cutlery is unpleasant. That's why modern „Henkelmann“-containers should be enameled inside. Enamel is nothing more than a glass coating applied to the metal. And eating and drinking from enameled tableware feels very pleasant.

For short-term take-away use on the bridges, correspondingly wafer-thin metal containers with enamel coating on the inside are used.

The metal of choice for these containers is stainless steel

The most important criteria in selecting the metal were (1) it should be common, (2) it should be durable, (3) it should have high durability ("strong") while being comparatively light, and (4) it should be suitable for food contact. Three (enameled) metals have been considered accordingly: Stainless steel, titanium and aluminum.

Stainless steel was chosen because of its frequent occurrence, durability and recycling potential, as well as its excellent food compatibility. In addition, stainless steel has another advantage: The market for recycled steel is already very large -the ratio of crude steel production to steel scrap use worldwide was 2:1 in 2015. Even if every household in Germany permanently had a set of 10 steel containers with an average volume of 250ml in use, a quarter of the end-of-life vehicles scrapped each year in Germany would already suffice as recycling material for their one-time production. The ecological rucksack for titanium and aluminum, on the other hand, is significantly larger, both in extraction and in the recycling process.

Stephen Barnes and Joe Cabral - alamy.com

A magnesium alloy would theoretically also have been a candidate. For this, however, the metal selection would have had to be extended to various alloys, which would have been beyond the scope of the feasibility study for the Frankfurt Bridges. The poor corrosion resistance and brittleness during processing make pure magnesium unsuitable as a pure material for dinnerware.

An important selection criterion for packaging: weight

Specific weights in comparison:

•Steel 7.5 to 8.5 gr/cm³

•Titanium 4.5 to 4.8 gr/cm³

•Aluminum about 2.7 gr/cm³

Steel has an average density of 7.85 g/cm³ (=7850 kg/m³) and is thus significantly heavier than aluminum and titanium for the same volume. Its weight disadvantage compared with lighter metals is compensated for by the strength of stainless steel: Since it has a higher tensile strength than aluminum or titanium, it can be processed thinner. This means that less material is needed for a vessel with the same strength.

The properties of stainless steel packaging are further massively improved by an additional enamel coating. In particular, the increased impact resistance, as well as the improved resistance to acids and alkalis, ensures a significant extension of the service life of a packaging.

An enameled stainless steel container with a capacity of 250 ml and a wall thickness of 1.5 mm weighs approx. 36 g, plus lid. An aluminum container, which would have to be about twice as thick to make it similarly impact-resistant, would then no longer be a third as light in terms of weight, but only slightly lighter.

Selection criterion: Sustainability

Sustainability can be measured using the ecological rucksack: Here it is made up of energy consumption and pollutant emissions during production and disposal, as well as service life. Titanium and aluminum are lighter than stainless steel, but their ecological rucksack is larger.

Although titanium is one of the most abundant elements in the earth's crust, it is extremely expensive due to the manufacturing process. This requires high temperatures, resulting in increased CO2 emissions. It also requires the use of chlorine, which is obtained in an energy-intensive process.

The Bayer process commonly used to extract aluminum from bauxite is also energy-intensive. It also produces a toxic residue known as red mud, which is difficult to dispose of.

Although the extraction of steel also requires a relatively large amount of energy, it can be recycled with less energy input than aluminum or titanium because it oxidizes less easily. If recycled steel is used, the ecological rucksack is improved. Added to this is the higher durability and thus service life.

The thermal conductivity of metal must be bypassed during take-away

To counter the thermal conductivity of metal, there are also special sheaths made of completely compostable biopolymer in which containers can be placed. The enamel coating on the inside of the stainless steel containers also slows down heat conduction.

In addition to steel, another reusable material has been identified for the packaging on the bridges that weighs less than stainless steel: glass has an average density of 2.5 g/cm³, so it is even lighter than aluminum and joins our porcelain dining tradition.

The second solution are hardened glass containers

Many people eat mostly from ceramic. However, this is heavy and therefore not suitable as a material for take-away containers. For eating similarly pleasant is glassware. Like stainless steel, it has many advantages: It is food safe, tasteless, can be cleaned hygienically and can be recycled. However, glass has one disadvantage: it breaks relatively easily. If you make the glass thicker, it becomes more break-resistant, but also heavier - and therefore more laborious and expensive to transport.

But there is a solution for this: tempered glass.

Glass can be hardened in two ways: thermally or chemically

With thermally tempered glass, the tension between the outer layer and the glass core is changed by heating the glass a second time. This makes it up to 15 percent more break-resistant. However, thermally tempered glass needs a certain thickness to maintain the temperature difference between the glass core and the outer layer. It cannot therefore be processed as thin as desired.

The situation is different with chemically tempered glass:

Here, sodium ions are interspersed with larger potassium ions on the glass surface: this densifies the glass surface. This multiplies the so-called flexural strength of the glass - colloquially: its hardness. Since no temperature difference between inner and outer layers is necessary, chemically tempered glass can be processed relatively thinly.

For the hardening of smartphone-glass, a similar process is used.

Particularly stable glass was available in the GDR with „superstrong" glasses

The chemically hardened "Superfest" glasses were available in every pub and household in the GDR. The manufacturing process was developed in the GDR at the end of the 1970s. At that time, they were looking for ways to make production more economical. The result was "Superfest" glasses, which were five times as hard as normal glasses and even survived falls from a height of 50 centimeters. Many of these glasses are still in use today. But like many things that drastically increase the service life of products - and would thus eventually lead to a saturated market - the process was not pursued further after the fall of the Berlin Wall, and all the machines were scrapped.

Interview with Dr. Dieter Patzig, chemist and inventor of Superfest glass

As noted by Dr. Patzig, the task in the GDR was similar to today's due to climate change: "(...) to produce raw material-saving, long-lasting glasses". The newly developed process consisted of spraying the drinking glasses formed by rotary blow molding at 430°C with potassium salt (degradable in Germany) instead of drawing them through a solution. In GDR times, 40,000 glasses per day were produced, which lasted up to 5 times as long as conventional pressed glasses. After 8 years of production until the end of the 80s, this meant that the market in the GDR was saturated. So then there was the idea to offer also chemically hardened packaging glasses, but this was never realized due to the reunification. Theoretically, anyone could revive this process, because the production is no secret: all patents are freely available online.

Energy-intensive glass production is worthwhile - but only in a reusable system

Like steel, glass is comparatively energy-intensive to manufacture: melting the input materials requires temperatures of over 1,000 °C.

As with stainless steel, however, the life cycle assessment of glass improves significantly if it is used long and frequently enough:

Chemically tempered glass therefore saves both material and energy:

Hardening significantly extends the service life of the containers. They need to be produced again less frequently, which saves material and energy.
As the glasses are more break-resistant, they can be manufactured thinner with the same strength. This also reduces the energy required for transport between the cleaning station, the catering trade and the consumer.

If, in addition, waste glass is used for production, the energy requirement is reduced a further time.

Break-resistant, relatively thin glass is a sustainable alternative to plastic take-away packaging and tableware

Research into glass technology for smartphones has led to rapid improvements in break resistance of glass over the last two decades: A wide variety of tempering processes and laminated glass materials have been developed.

The experience gained from these research fields should be used for the further development of take-away tableware made of break-resistant glass.

Transport, cleaning and other process energy can always be expended during the day when photovoltaically generated electricity is abundant. They are cleaned with the help of steam and UV radiation, i.e. with comparatively little water or detergent.

In addition, packaging made of lightweight, break-resistant glass or thin enamelled stainless steel fulfils another important criterion: Even if they end up somewhere in the environment, break or are disposed of incorrectly - they leave no microplastics behind.

The range of containers is so wide that there is a suitable one for every dish

For some dishes, you need containers with several compartments, for example, for Asian dishes, where the main course and rice should be kept separate. For noodle dishes, soups and the like, on the other hand, no subdivision is necessary. Containers with two or more compartments are made of metal because it is easier to shape than glass. Containers without divisions are made of glass.

For fried foods and for foods with special shapes, such as burgers, there will be cans made of metal that are modeled after the previous cardboard boxes in terms of shape. Holes in the metal allow heat and steam to escape. This keeps the food fresh.

And there are also special take-away packagings for special cases

What about pizza and Doner kebab? Pizzas will continue to be delivered in folding boxes. In the medium term, the aim here is to switch to materials with a better eco-balance than paper. For example, leftover cocoa shells could be used for the packaging. There is also a wide range of containers made from plant waste already on the market. These are food-grade and degrade completely.

Doner kebabs can still be packaged in aluminum foil, as the disposal concept of the Frankfurt Bridges also provides for metal separation. The aluminum is thus recycled.

Another important sustainability lever for take-away containers: Adapted portion sizes eliminate the need to throw away food and save resources

Another form of resource waste is leftovers that are thrown away because standard portions are too large for many people. Therefore, another requirement for restaurants on bridges is to offer small, medium and large portions at proportional prices. Without proportional pricing, it's easy to tend to buy too much because, after all, it only costs a little more. But carelessness results in waste: not only of food, but also of the energy used to produce and transport it.

Efficiently designed reusable systems are the most sustainable solution – and convenient and fast return options are important aspects of consumer acceptance

Every catering business that offers food for direct consumption on the Frankfurt Bridges undertakes to participate in the bridge reusable system. According to the German government's amendment to the Packaging Act, vendors are to offer a "recyclable alternative" to all take-away packaging from 2023, anyway.

But many different solutions do not make the world any simpler. A uniform bridge-wide system therefore offers caterers and customers an environmentally friendly and resource-saving reusable system that is as simple as a single-use system.

Depending on the food and portion size, there are different reusable containers for the take-away area. Like any reusable system, the system on the bridges also works with a deposit.

But who wants to carry the coffee mug or dinner set back to where it was bought? Most of the time you would stroll on, look for a bench in a park or walk home with it.

Take-away packaging can be returned to 300 collection machines on the bridges

On the bridges, there are round collection machines about every 500 meters (in more densely built-up sections, every 50 to 100 meters). Beautifully designed on the outside (whether ultra-modern, baroque or fancy - in any case artistic), inside they all consist of "mini dishwashers" mounted in a rondel around the central axis of the cylindrical vending machine. Each vending machine has three such rondels inside, one above the other.

Correspondingly, each vending machine also has sliding windows on three levels, which open when the bridge card is scanned. Through the open sliding window, you can put the dirty reusable tableware into the "mini dishwasher". When the window closes, the filled "mini dishwasher" moves on, and the next (still empty "mini dishwasher" on the traffic circle) moves up. The deposit paid for the catering containers is credited back to the card. Everything can be viewed in an app.

Color-matched photovoltaic modules with battery island solutions are attached to the top of the vending machine so that the energy for operation can be partly drawn from it.

The collection machines are not installed, i.e. they are not connected to the bridge wastewater network, but only to the bridge power network. They are de facto dishwashers in the outdoor area, but they do not perform a complete cleaning, only a pre-cleaning.

Next to the collection machines are separate trash cans for leftover food, any bags that may be produced, etc. These trash cans are connected to the waste disposal pipes of the Frankfurt Bridges.

The cleaning process begins on site in the collection machine

It will be possible to put the used take-away containers and tableware into small, separate mini dishwashers, which are self-contained units, because when the sliding window is opened, no other dishes with food remains must be seen or smelled.

Once a mini dishwasher has been filled with its containers, cutlery, glasses etc. through the window, the window closes, the mini dishwasher is moved one place further from the roundel (so that the next, still empty mini dishwasher comes to stand behind the sliding window) and then all take-away containers etc. in the mini dishwasher are briefly filled with hot steam and then irradiated with UV light to kill germs. The mini dishwasher carries the water for the steam with it and receives the electricity via contact surfaces with the electronics in the Rondell core.

This is not yet the actual cleaning, but merely serves to ensure that when the containers are collected and taken to central cleaning sites, they do not arrive there germ-ridden and fungus-ridden.

As soon as all the mini dishwashers have been filled in all three rondels of the machine, the collection machine sends a signal to a vehicle that -driving autonomously- comes and collects the three inner rondels: The easiest way to do this is to have half of the vending machine housing consist of doors that open, the rondel core together with the three rondels and their mini dishwashers is lifted by rotating trolleys and transported into the car, from which a new empty rondel unit comes and takes the place of the old one in the collecting vending machine.

The vehicle brings the rondel units to the railing of the FES, and after the containers have been centrally cleaned in accordance with regulations in a facility specially built there, they are returned to the catering trade on the bridges according to the quantities ordered.

The prerequisite: The consumer plays along and fills the mini dishwashers just like his own at home: without food leftovers or foreign objects - which the collection machine, however, also registers with sensors and can assign to the respective bridge card of the user - and, if necessary, book a fine via deposit deduction.

Moreover, Take-away containers can be used in a variety of ways: unpackaged stores, for example, can also keep the containers on hand for their customers

Theoretically, the jars would also be ideal for home-cooked lunches on the go.

Food leftovers can be disposed of next to the roundels in bio-waste garbage cans connected to the pneumatic disposal tubes of the Frankfurt Bridges

There are cleaners on the bridges during the day - but bridge dwellers and residents, the expected large number of tourists and Park&Ride users from the Frankfurt area are likely to ensure an extraordinarily high volume of waste on the bridges that goes beyond take-away leftovers. It therefore makes sense to provide the bridges with a separation waste garbage can system connected to pneumatic tubes (located in or under the body of the bridges), as has already been implemented in Songdo/Korea and has also been designed for New York's Highline: There, a study commissioned by the NY Department for Transportation even considers connecting neighboring buildings to the "pneumatic waste disposal system".

Conclusion: A sustainable reusable system without plastic is created for takeaways on the bridges

Enameled thin stainless steel and more break-resistant, relatively thin - and thus also somewhat lighter - glass meet the criteria of the packaging regulations: properly treated and with the appropriate disposal process, they are definitely reusable. Stainless steel can be expected to last for several decades, while sturdy glass can be expected to last for years. At the end of their use cycle, both materials are easily recyclable.

Even though both materials are relatively energy-intensive to produce, the long service life means that the energy expenditure is recouped relatively quickly. If the containers are recycled, the energy balance is even better.

They also meet another important criterion: even if they end up somewhere in the environment, break or are disposed of incorrectly - they leave no microplastics behind.

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