Stainless Steel Grades: SUS304 vs. SUS316

Food machinery spec sheets often say "SUS304" or "SUS316." These are the two most common austenitic stainless steels; SUS is the Japanese Industrial Standards (JIS) designation, corresponding to American AISI 304 and 316.

What's the Difference?

• SUS304: Commonly called 18-8 stainless steel, it contains about 18% chromium and 8% nickel. According to the Nickel Institute, 304 is the alloy most commonly used in food and beverage applications, the standard for everything from milk to beer.
• SUS316: Slightly higher nickel content than 304, with 2–3% molybdenum added. Molybdenum makes it more resistant to pitting (corrosion that forms small pits on the surface) in chloride environments.

There are also 304L and 316L, where L means low carbon, which makes them less prone to intergranular corrosion near welds after welding; they're commonly used in welded structures.

Should My Machine Be 304 or 316?

The deciding factors are chloride ions and acid. Sources of chlorine in a food factory include:

• Salt in the ingredients themselves, such as pickles, sauces, and seafood.
• Chlorine-based sanitizers, such as sodium hypochlorite (bleach).
• Chlorine in water, and salt in the air in coastal areas.

General principles:

• Typical dough products, red bean paste, taro paste, sweet potato products: Low in salt, so 304 is usually sufficient.
• High-salt, acidic, seafood, meat: The Nickel Institute notes that 316L can be used for fish and meat; in environments with high temperature combined with high acidity and high chloride, 304 may not hold up.
• Harsher environments: Soy sauce production, for example, may require higher-grade alloys.

Choosing 304 doesn't mean you can't use bleach; what matters is concentration, contact time, and rinsing. Rinsing thoroughly with clean water after sanitizing and not letting sanitizer sit on the surface for long reduces corrosion.

What Are the Food-Contact Parts Made Of?

A food machine isn't made entirely of one material. A common configuration:

• Food-contact parts: The hopper, screw, nozzle, cutting pieces, and conveying surfaces commonly use stainless steel or food-grade plastic.
• Non-food-contact parts: The frame and housing may be stainless steel or other materials.

For the material specifications of each Dong-Yih Machinery model, please call us (06-257-4644).

What Do the Regulations Say?

Taiwan's regulations don't specify that "304 or 316 must be used"; instead, they set conditions the material must meet:

• Act Governing Food Safety and Sanitation (食品安全衛生管理法) Article 3: Machinery that comes into direct contact with food counts as "food utensils."
• Sanitation Standard for Food Utensils, Containers and Packages (食品器具容器包裝衛生標準) (last amended January 11, 2023), Article 6, Annex Table 1: For "metal alloys, where the surface in direct contact with food is a metal alloy," the material must contain no more than 0.1% lead and 5% antimony; in migration testing, no more than 0.2 ppm arsenic, 0.4 ppm lead, and 0.1 ppm cadmium.
• Standards for Food Factory Construction and Equipment (食品工廠建築及設備設廠標準) Article 7: Food-contact equipment materials must be non-absorbent, corrosion-resistant, and not produce toxins or odors.
• Regulations on Good Hygiene Practice for Food (食品良好衛生規範準則) Annex 2: Food-contact surfaces must be smooth, free of dents or cracks, and kept clean.

Internationally, the European Hygienic Engineering & Design Group (EHEDG) also publishes guidelines on materials for food-contact equipment that can serve as a design reference.

When Is 316 Used?

Here are questions to ask yourself when choosing:

1. Is your product or sauce high in salt? Is it acidic?
2. Do you use chlorine-based sanitizers daily? At what concentration and for how long?
3. Is there high-temperature heating together with salt or acid?
4. Is your factory near the sea?

If most answers are "yes," you can discuss switching the contact parts to 316 with the machine maker. 316 usually has higher material costs, and you don't necessarily need to change the whole machine; you can target only the food-contact parts most prone to corrosion.

Maintenance Makes Stainless Steel Last Longer

• Don't scrub with steel brushes or iron-containing scouring pads, to avoid iron particles adhering and causing rust.
• Use detergents and sanitizers at the labeled concentration, then rinse and dry.
• Regularly check welds and dead spots for discoloration or rust spots.

FAQ

Q: What's the difference between SUS304 and SUS316?
A: 316 adds 2–3% molybdenum, giving it better resistance than 304 to pitting in chloride and salty environments.

Q: Is 304 enough for making steamed buns and mantou?
A: Typical dough products and red bean paste are low in salt, so 304 is usually sufficient; for high-salt or acidic products or frequent chlorine sanitizing, consider 316.

Q: Do regulations require food machinery to use 316?
A: No grade is specified. Annex Table 1 of the Sanitation Standard for Food Utensils, Containers and Packages sets lead and antimony content and migration limits for metal contact surfaces.

Q: Why does stainless steel still rust?
A: Chloride ions, residual sanitizer, and adhering iron particles can all cause corrosion; rinse and dry after cleaning, and don't use steel brushes.