Stainless steel question

by Mike in KY » Jan 13th, '06, 11:06

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While I may favor glass for serving tea, I recently decided to purchase a 1-liter stainless steel Savoy teapot for occasions where clumsy folks might be around. We all know those individuals whose eyes widen in horror at the mere sight of a glass teapot, their hearts racing at the thought of potential accidents. It's amusing to watch, but better from a distance, preferably in someone else's home. It's ironic, of course, considering that if they were truly that accident-prone, they might have met a tragic fate long before birth.

Now, onto the issue at hand. I thoroughly cleaned the pot, scrubbing it with baking soda, using a spout brush, and placing it on the bottom rack of the dishwasher for three cycles. I even brewed several batches of tea to help break it in. Yet, I still encounter a problem. If I leave tea in the pot for just half an hour, it continues to darken and develops a strong, unpleasant taste. It's unfortunate because it retains heat better than any glass or ceramic options. There are no tea leaves in the brew, indicating a potential reaction with the metal. In contrast, I have a Corning Thermique thermos that keeps tea fresh for hours without losing flavor or color.

What could be the reason for the tea's deterioration in this stainless steel pot?

Can stainless steel cups affect the quality of tea?

This topic has garnered significant media attention, with some individuals conducting specific experiments: they used a new stainless steel water cup, brewed tea in it, sealed the cup tightly, and allowed it to sit undisturbed for 72 hours. Following this, the cup showed signs of corrosion. Experts explained that stainless steel contains chromium, which can leach into the tea.

Chromium is a toxic heavy metal; however, it doesn't mean that brewing tea in stainless steel cups is unsafe. This conclusion sparked considerable debate. So, what’s the real story?

Contrary to popular belief, stainless steel can rust. The name "stainless steel" might lead one to assume it never rusts, but in reality, it is simply less susceptible. The corrosion resistance of stainless steel largely depends on the chromium content. When the chromium reaches a level of 12%, it can spontaneously create a thin passivation layer in an oxidative environment to prevent further oxidation and corrosion, making it suitable for everyday use. Nonetheless, exposure to acids, alkalis, or salts can cause corrosion if the protective layer is compromised.

This means that for visible corrosion to develop, there must be prolonged and severe corrosive conditions. Tea itself is nearly neutral, with very low ionic strength, making it nearly harmless to stainless steel, and unable to cause visible corrosion over a short duration.

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In food production, numerous tools are crafted from stainless steel, which can endure higher acidity levels for extended periods. If corrosion in tea brewing were as apparent as described in the experiments, such equipment would require immediate replacement. The corrosion seen in those tests was likely just tea residue accumulating on the cup.

Risk Evaluation.

Chromium is indeed present in stainless steel, and theoretically, it can migrate into food or drink. However, food-grade stainless steel adheres to strict national standards that regulate the levels of chromium migration under specific conditions.

Given the health concerns surrounding chromium (especially hexavalent chromium), stringent regulations exist worldwide governing its migration from stainless steel utensils. According to relevant Chinese standards, chromium migration from stainless steel must not exceed 0.4 mg/m2, typically measured by boiling in 4% acetic acid for 30 minutes and subsequent immersion for 24 hours. The pH of such acetic acid is approximately 2.5. This implies that after a 30-minute boil and a 24-hour soak, the chromium migration from each square decimeter must remain under 0.4 mg.

Unlike acidic solutions, tea has a much lower acidity (ranging from 5 to 7 depending on the type) and minimally impacts stainless steel. If tea at a pH of 5.5 were used for similar immersion tests, it would take around 246 hours to migrate 0.4 mg of chromium, or nearly 10 full days—only achievable if the stainless steel were devoid of its protective layer and actively reacting throughout the duration.

In reality, tea isn't typically boiled in stainless steel for 30 minutes, and considering the passivation layer, the actual reaction rate will be slower. Thus, as long as you use a standard stainless steel cup, you need not worry about prolonged tea storage resulting in harmful chromium migration.

Food is inherently complex, and with increasingly advanced testing technologies, finding "harmful components" is common. But, it's essential to remember that "toxicity concerns must consider dosage."

Under normal circumstances, even if chromium does leach, it remains harmless. Claims suggesting that chromium released from stainless steel cups poses significant health risks lack substantial grounding based on factual data.

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