Safe Food Preparation Using Stainless Steel

Summary of a report prepared by the KTH Royal Institute of Technology on behalf of Team Stainless

www.teamstainless.org

Executive summary

Stainless steel has played a key role in the production and preparation of food and drink for over 70 years. It is chemically inert and its constituent metals do not react with or transfer to food in any significant way.

Stainless steel is also non-toxic and can be manufactured into smooth, non-absorbent surfaces, equipment and utensils which can be safely cleaned, disinfected and sterilised without the risk of corrosion. It does not taint food and is highly resistant to the wide range and rapid changes of temperature frequently encountered in food production.

The new protocol

In 2013, the Council of Europe (CoE) published a new guideline onmetals and alloys in food contact materials, with prescribed limits formetal transference and a new, more aggressive test to simulate use in food preparation.

Team Stainless, a consortium of stainless steel and alloying elementassociations, commissioned the internationally renowned KTH RoyalInstitute of Technology in Sweden to independently test seven gradesof stainless steel in accordance with the new protocol.

The study demonstrated that all the grades tested are safe to use forfood preparation as the amounts of metals released were below the limits prescribed in the CoE guidelines. The study also demonstratedthat the rate of metal release decreases significantly following initial exposure and with repeated use over time.

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The context of the study

Metals and alloys can be released by leaching under certaincircumstances. For metal products in contact with food, such as pots and pans for example, it is important to ensurethat the amounts released under all conditions are well below levels that would give cause for concern for human health.

Because stainless steel is an inert alloy it is inherently stable. Only vanishingly small amounts of metal are releasedin contact with foods, which is one of the main reasons whystainless steel has largely replaced other metals used in foodpreparation.

All of the evidence supports the conclusion that stainless steelis completely safe for all food and drink use.

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Regulation

In Europe, the Framework Regulation (EC) 1935/2004 specifically requires that “food contact materials are safe; and must not transfertheir constituents to foods in quantities which could endangerhuman health, change food composition in an unacceptable way or deteriorate its taste and odour”.

The Council of Europe (CoE) published new guidelines regarding metals and alloys in food contact materials in 2013. These define Specific Release Limits (SRLs) for iron, chromium, nickel, manganese and molybdenum. The guidelines also include a new test protocol using a solution of citric acid as a food simulant, which is more aggressive to stainless steel than the acetic acid used in the previous tests.

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KTH study

The new guidelines presented an ideal opportunity for the industryto reconfirm the safety of using stainless steel in all types of food preparation. Team Stainless commissioned KTH to test sevengrades of stainless steel in line with the new guidelines.

As well as some different procedures, these vary from earlier tests by using citric acid as the food stimulant, rather than aceticacid. Citric acid is widely used in a range of acidic and alkalinefoods and is a more aggressive simulant.

The seven grades tested were selected from lower-alloyed gradesup to high alloy materials to give a complete picture and includedthe two most common grades.

All samples were professionally prepared in laboratory conditionsand tested with 5g/l citric acid (pH 2.4) for two hours at 70 °C, followed by two further periods of 24 hours and 238 hours at 40 °C.

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Note: For simplicity the 24 hour results are omitted here, but they also passed the CoE testrelease limit requirements and they can be found in the full report.

Results of the study

For the relevant metallic elements of stainless steel, referred to below, all seven tested grades passed the test stipulated by the CoE guidelines. The study demonstrated that only small amounts of metals were released from all the gradestested, and that the levels were all below the Specific Release Limits (SRLs), for all exposure scenarios. This confirms that stainless steel is safe to use and acceptable as a food contact material.

The diagrams below show the SRL for each metal at the top of the x-axis, and the grades tested along the y-axis. The bar for each grade shows the total amount released, showing the results after 2 hours and after 240 hours exposure.

SRL 40 µg/cm2

Iron

Chromium

40

35

25

30

20

10

15

5

0

0.25

0.2

0.15

0.1

0.05

0

Re

lea

se

d a

mo

un

t (µ

g/c

m2)

Re

lea

se

d a

mo

un

t (µ

g/c

m2)

Grade

–S409771.4003

ASTMUNSEN

430S430001.4016

204S20431 (+Cu)1.4597 (+Cu)

201S201001.4372

316LS316031.4404

304S304001.4301

–S321011.4162

Grade

–S409771.4003

ASTMUNSEN

430S430001.4016

204S20431 (+Cu)1.4597 (+Cu)

201S201001.4372

316LS316031.4404

304S304001.4301

–S321011.4162

SRL 0.25 µg/cm2

2–240 hours

0–2 hours

2–240 hours

0–2 hours

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The study was able to demonstrate that the release rate of metals decreased significantly after initial exposureand with repeated use.

A more detailed technical summary of the report can bedownloaded from http://bit.ly/1USTJjn. The full report is also available from http://bit.ly/1Y8gAfd.

SRL 0.14 µg/cm2

Nickel

0.02

0

Re

lea

se

d a

mo

un

t (µ

g/c

m2)

SRL 1.8 µg/cm2

Manganese

Re

lea

se

d a

mo

un

t (µ

g/c

m2)

SRL 0.12 µg/cm2

Molybdenum

Re

lea

se

d a

mo

un

t (µ

g/c

m2)

7

0.04

0.06

0.08

0.1

0.12

0.14

0.2

0

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0.02

0

0.04

0.06

0.08

0.1

0.12

2–240 hours

0–2 hours

2–240 hours

0–2 hours

2–240 hours

0–2 hours

Grade

ASTMUNSEN

316LS316031.4404

Grade

ASTMUNSEN

204S20431 (+Cu)1.4597 (+Cu)

201S201001.4372

316LS316031.4404

304S304001.4301

–S321011.4162

Grade

ASTMUNSEN

204S20431 (+Cu)1.4597 (+Cu)

201S201001.4372

316LS316031.4404

304S304001.4301

–S321011.4162

Image courtesy of IMOA (title), fotolia.com/DDRockstar (p. 3), fotolia.com/JackF (p. 4), istockphoto/GregorBister (p. 5 left), istockphoto/alacatr (p. 5 right); layout and design: Martina Helzel, circa drei www.teamstainless.org