Putting ZWILLING knives at the cutting edge of sustainability

Outokumpu Circle Green: Putting ZWILLING knives at the cutting edge of sustainability

The first knife series that will be equipped with Outokumpu’s unique stainless steel grade Circle Green is ZWILLING Pro, one of the highest-selling knife series of ZWILLING

ZWILLING, one of the global leading suppliers of high-quality products for modern home kitchens,  is using Outokumpu’s Circle Green Dura to transition major knife series to the world’s first towards-zero stainless steel. With a more sustainable ZWILLING Pro series the premium brand aims to sharpen its competitive edge with the growing number of consumers who want to protect the environment. 


“People have always thought of ZWILLING as a manufacturer of high-quality knives, but we also want them to think of us when they think of sustainability,” says Gernot Strehl, Head of Product Compliance for ZWILLING. “Being first with a series of sustainable knives will reinforce this message and help us stand out from other brands.”

ZWILLING is already well on its way to achieving its goal of a carbon-neutral product portfolio. For example, by sourcing green electricity to power energy-intensive heat treatment and grinding processes at its Solingen factory, it has slashed the carbon footprint of its products by an average 30 percent.

Furthermore, ZWILLING is also eliminating plastic packaging and increasing the recycling and circularity of materials wherever possible. It is also working to achieve FSC (Forest Stewardship Council) certification for the wood used in knife blocks and handles.

However, one major challenge remained. That was sourcing low-emission stainless steel. This was especially vital since the material represents a high proportion of its knives by weight. And that is where Outokumpu and STAHL KREBS, the Solingen-based steel distributor, come in.


Gernot Strehl’s role is to oversee the quality of materials that ZWILLING uses, and particularly steel. He says: “When we carried out a life cycle assessment to understand the scale and source of CO2 emissions in our products, we realized that much of our carbon footprint is embedded in the raw materials that we source. As a first step in sourcing low-emission stainless steel, we asked suppliers about their rates of recycling and use of fossil-free energy sources". 

“Then we learned about Outokumpu’s Circle Green initiative through our partner STAHL KREBS. We quickly saw that it offered the opportunity to cut the carbon footprint of our knives by around a third. Combined with sourcing green electricity, that enables us to halve our product related emissions for knives.” 


Durability as the first measure of sustainability

While cutting emissions is important, it’s worth remembering that by making a product that stands the test of time, ZWILLING makes the most of the energy and raw materials used to make knives.

Gernot Strehl says: “Durable materials and careful production mean that our knives last 30 years or more. We can see this when customers visit our service center, asking us to re-sharpen knives they’ve inherited from parents or grandparents". 

“High-quality steel is essential to achieving this. We use a special alloy that we developed in-house decades ago. It’s based on a martensitic grade of stainless steel with adapted levels of alloying elements for enhanced hardness and corrosion resistance. We produced this at our own steel mill until the early 1960s, when we licensed production to a mill that has since become part of Outokumpu.”

During the same period, ZWILLING also initiated its long-standing relationship with steel distributor STAHL KREBS, which looks after logistics, storage and stock services. In turn, this optimizes steel deliveries to maximize efficient knife production. 


A partnership going back for generations

STAHL KREBS played an important role in sourcing of the new Circle Green material from Outokumpu. 

Daniel Krebs, Managing Director of STAHL KREBS, says: “It’s exciting to play a role in delivering the first towards zero high performance stainless steel. We are a fifth-generation family business and we among other business specialize  in supplying martensitic grades for knives, surgical instruments and other blades. We’ve been working with Outokumpu since 1911 and over the years have helped to develop new alloys.

As a distributor, STAHL KREBS needs to deliver the right materials in the right quality and quantity at the right time and with sometimes challenging specifications. However, Outokumpu produces steel in large batches of up to 120 tons. Therefore, the distributor balances supply and demand to ensure customers receive a steady supply of material. This role has enabled it to develop close working relationships with both customers and steel producers. That position enables it to bring people together to share knowledge and innovative approaches.

Daniel Krebs continues:

“We know the biggest difference we can make in helping customers on their journey towards a decarbonized future is by encouraging the market for sustainable steel. Therefore, in our very first discussions with Outokumpu about sustainable martensitic stainless steel two years ago, we knew right away it was a perfect fit for ZWILLING. So we connected the two and are excited to see the results.”


How does Circle Green compare with standard stainless steel?

Circle Green is not a new grade, but rather a new sustainable philosophy for producing stainless steel. Products that bear the Circle Green symbol are physically, chemically and mechanically identical to existing stainless steels. The only difference is that Outokumpu has made extreme efforts to minimize emissions at every step of production. 

The philosophy includes sourcing and processing of low-emission alloying elements and ferrochrome. It also maximizes recycled content and uses 100 percent low carbon electricity to power steelmaking processes such as the electric arc furnace (EAF). 

The result is that Circle Green stainless steel has the lowest carbon footprint in the world. For some grades, Outokumpu can reduce emissions by 93 percent compared to the industry average, although this varies, depending on the grade and the alloying contents required. 

Initially, Circle Green production focused mainly on the most widely used grades of stainless steel, such as Core 304/4301 and Supra 316L/4404. Some of the first customers for these are in the appliances and automotive industry.

However, knife production requires more specialist martensitic stainless steels and other high-performance alloys. Two years of development work culminated recently with Outokumpu sending ZWILLING the first delivery of its Circle Green Dura grade.


Making a change for series production

As a first step in shifting production to the low-emission material, ZWILLING is adopting the Circle Green Dura stainless steel for its ZWILLING Pro series of knives. 

Gernot Strehl says “Although Circle Green stainless steel is chemically identical to our special formula stainless steel, we needed to be sure that it offers the same experience and long life for our customers. We were concerned that a small change in production at the steel mill to save carbon emissions might potentially alter the performance of the steel". 

“We evaluated corrosion resistance with testing according to the standard applied for knives, as well as dishwasher testing. We also compared heat treatment performance and found there are no differences between Circle Green and our original material. This shows that Outokumpu has kept the promise it made in terms of consistent quality.”

ZWILLING is also making other changes at its factory to ensure traceability and separation. This will ensure it can identify and track blades based on the new material at every step of production, from material delivery to packaging. This will reinforce the benefits customers get from choosing knives manufactured from sustainable materials.


Sustainable ZWILLING Pro knife series

 Zwilling PRO Special Edition Knife block set_Earth DayThe first knife series that is equipped with Outokumpu’s unique stainless steel grade Circle Green is ZWILLING Pro, one of the highest-selling knife series of ZWILLING


The plan is for ZWILLING to introduce the new sustainable ZWILLING Pro series, combining best practice in low-emission steel production and sustainable forestry, at the same price as its existing products, simply because it sees sustainability as becoming an essential element for customers. While there is a premium to pay for using Circle Green, the investment will set ZWILLING apart. It is also a great opportunity to confirm the market’s appetite for sustainability. 

Gernot Strehl comments:

“Interest in sustainability is growing fast and a lot of retailers are asking us to share data such as carbon footprint and recycled content. In the long term, we’re aiming to convert all of major knife series to sustainable materials but that will take time. In the meantime, we’re looking forward to seeing how consumers react to the first sustainable premium knife made from Circle Green, with a stainless steel carbon footprint that is half of other knives on the market.”


Having taken delivery of its first batch of Outokumpu’s Circle Green Dura in November 2023, ZWILLING is now focusing on production, product development and marketing plans. Although it is too early to share details, the first sustainable premium knife series with Circle Green stainless steel will be launched during 2024. ZWILLING is also considering joining Outokumpu’s Inner Circle® initiative for the efficient return of scrap stainless steel for recycling. 

Meanwhile, STAHL KREBS is hopeful that knife and blade producers in other segments see an advantage in towards zero stainless steel. Daniel Krebs concludes: “By producing the first sustainable premium knife with Circle Green stainless steel, ZWILLING is gaining a first-mover advantage and showing its customers that it’s listening to the climate debate and taking action. Today’s consumers have a lot of power and being first to market means having the strongest voice and the best data to back up sustainability claims. For us as a distributor, it’s a great way to show our customers what is possible in terms of sustainable production.”

Read more: Chopping emissions: ZWILLING launches special edition Earth Day knives made with Outokumpu Circle Green®

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