Stainless steel

Stainless Steel is a common name for metal alloys that consist of 10.5% or more Chromium (Cr) and more than 50% Iron (Fe). Although it is called "stainless", a better term for it is "highly stain resistant". A somewhat dark metal, it looks bright because it reflects light.

What are the main benefits of stainless steel in kitchen utensils?

♦ It is one of the most hygienic surfaces for the preparation of foods and very easy to clean, as its unique surface has no pores or cracks to harbor dirt, grime or bacteria.
♦ It is very attractive and requires minimal care, since it won't chip or easily rust and it takes little seasoning.
♦ It will not affect flavor, as it does not react with acidic foods during food preparation or cooking.
♦ With proper care, it has a useful life expectancy of over 100 years, and it is totally recyclable.

What gives stainless steel its properties?

The chromium content in stainless steel alloys is what generally prevents corrosion. Pure iron, the primary element of stainless steel, is extracted from its natural state as iron ore, it is unstable by itself, and naturally wants to corrode (rust). The chromium helps to procrastinate nature's attempts to combine the pure iron with oxygen and water to form rust.

The chromium works by reacting with oxygen to form a tough, adherent, invisible, passive layer of chromium oxide film on the steel surface. If damaged mechanically or chemically, this film is self healing as long as it has enough oxygen.

Because oxygen is necessary for the reaction, liquids and other foodstuffs stored for a prolonged time in stainless can prevent oxygen contact and thus promote corrosion, as can prolonged contact with household cleaners such as bleach.

Generally, an increase of chromium content improves the corrosion resistance of stainless steels. The addition of nickel is used to raise the general corrosion resistance required in more aggressive usage or conditions. The presence of molybdenum (Mo) improves the localized corrosion resistance, such as against pitting (scarring).

Other alloying metals are also used to improve the structure and properties of stainless steels, such as Titanium, Vanadium and Copper. Non metal additions typically include natural elements such as Carbon & Nitrogen, as well as Silicon.

High-carbon stainless steel contains a minimum of 0.3% carbon. The higher the carbon content, the less formable and the tougher the steel becomes. Its hardness makes it suitable for things such as cutting edges, and other high-wear applications like plow blades. Carbon thus helps makes the edge easier to sharpen, and helps retain a sharp edge longer.

How can stainless steel affect my health?

The principal elements in stainless that have effects on our health are iron, chromium and nickel.

♦ Iron can be very beneficial and a required mineral in a normal diet.
♦ Chromium is also beneficial in small quantities, and you would have to cook four complete meals in the same stainless steel pots every day to come anywhere close to reaching any adverse affects from chromium intake.
♦ Although nickel is poisonous in large quantities, only trace amounts go into the food - not enough to make a difference. The few who are allergic to nickel, however, should avoid using stainless altogether.

What precautions do I need to take when using stainless steel in my kitchen?
♦ To prevent hot spots when using stovetop cookware, it should have a heat diffusing base, either visible or encapsulated, that is made of a better heat-diffusing material, like copper or aluminum. These metals are highly conductive of heat, so use moderate heat to maximize the even spreading of heat, minimize sticking, and to get tastier, more evenly cooked food with less stirring.
♦ Do not store food or liquids in stainless steel cookware after cooking.
♦ To keep the surface smooth and scratch-free, do not use abrasives, bleach or ammonia. See cleaning instructions below.

How do I clean stainless steel cookware?
♦ To remove manufacturer or price stickers from cookware... Soak the area with warm water, then scrape off with your fingernail or with a hard-plastic spatula. A bit of rubbing alcohol, or a citrus oil based cleaner, will remove any remaining glue.

♦ When using a pan for the first time... Wash it well with soapy warm water and dry thoroughly. We recommend washing by hand.

♦ Whitish or chalkish deposits inside pan... Remove calcium deposits by boiling water with some white vinegar, allowing your pan to cool, then washing it with warm, soapy water. Help prevent white spots and pitting by adding salt to your cookware only after the water has reached a boil.

♦ Burnt food is stuck in pan... Cover the stuck foodstuffs with warm soapy water, allow to soak for some time, then boil for 10 minutes, allow it to cool, then use a soft cloth, or a nylon scourer if stubborn, and warm, soapy water.

♦ Still not clean out of the dishwasher... You might select a Pre-wash cycle if your pan's instructions indicate it is safe to clean in the dishwasher.

♦ Spills or overflows... Wash or clean the exterior before placing it again over heat.

♦ Filled pan left to cool on stove and lid won't come off... Warm the pan, then twist the lid to remove it.

♦ Left empty on heated surface... Allow it to cool slowly; do not immerse it in cold water.

♦ Stainless pan was left on heated surface, liquid has dried and yellow or blue streaks appear... On polished stainless, use a metal cleaner, such as Wenol or Red Bear, with a soft cloth. On satin stainless, use a nylon scourer, such as Scotch-Brite.

♦ Scratches on surface after washing repeatedly... Change your cleaning product to a gentler kind, such as Bon Ami.

♦ Cleaners not recommended for stainless surfaces... Bleach or ammonia should not be used on stainless steel.

How do I clean stainless steel knives?
The easiest and safest way to clean knives is to wipe them during and immediately after use, before food gets a chance to stick and dry on the blade. That's one of the reasons why professional cooks have a dish towel tucked at their waist.

Be sure to use caution when cleaning knives, to prevent cuts. Always draw the knife away from its cutting edge on the towel, starting near the handle. (Use caution.)

How are stainless steels classified?
The three major classes of stainless steel are:
♦ Austenitic: Chromium-nickel-iron alloys with 16-26% chromium, 6-22% nickel (Ni), and low carbon content, with non-magnetic properties (if annealed - working it at low temperatures, then heated and cooled). Nickel increases corrosion resistance. Hardenable by cold-working (worked at low temperatures) as well as tempering (heated then cooled). Type 304 (S30400) or "18/8" (18% chromium 8% nickel), is the most commonly used grade or composition.
♦ Martensitic: Chromium-iron alloys with 10.5-17% chromium and carefully controlled carbon content, hardenable by quenching (quickly cooled in water or oil) and tempering (heated then cooled). It has magnetic properties. Commonly used in knives. Martensitic grades are strong and hard, but are brittle and difficult to form and weld. Type 420 (S42000) is a typical example.
♦ Ferritic: Chromium-iron alloys with 17-27% chromium and low carbon content, with magnetic properties. Cooking utensils made of this type contain the higher chromium levels. Type 430 is the most commonly used ferritic.
Two additional classes worth mentioning include Duplex (with austenitic and ferritic structures), and Precipitation Hardening stainless steel, used in certain extreme conditions.

How are different classes of stainless steels used?
The austenitic microstructure is most commonly used for knives and cooking utensils. It is very tough, hardened through a process that consists of heating, cooling and heating. It resists scaling and retains strength at high temperatures.

Both ferritics and austenitics are used in kitchenware and household appliances. Austenitics are preferred in the food industry and beverage equipment due to the superior corrosion resistance and ease of cleaning. Type 301, for example, is an austenitic stainless steel, with 17% chromium, 7% nickel, and .05% carbon, and is widely used for institutional food preparation utensils.

You can easily make do with the lesser quality cookware for most oven use. For stovetop cooking, however, don't skimp on quality; buy only the better ones. Most manufacturers of high quality cookware use stainless steel similar to the Type 304 grade, with thick heat diffusing bottoms. Metals that provide better diffusion of heat, such as copper and aluminum, are attached to the bottom for heat diffusion, to prevent hot spots and uneven cooking.

Low quality cutlery is generally made out of grades like 409 and 430 (ferritic), while the finest Sheffield cutlery uses specially produced 410 and 420 (martensitic) for the knives, and 304 (austenitic) for the spoons and forks. Grades like the 410/420 can be hardened and tempered so that the knife blades will take a sharp edge, whereas the more ductile 304 stainless is easier to work and therefore more suitable for objects that have to undergo numerous shaping, buffing and grinding processes.

The best quality stainless steel knife blades have a high carbon content, and usually have molybdenum and vanadium in their composition.