The following products are never kosher (unless they show a certification symbol with the name of the issuing authority)

• Caviar and lumpfish eggs
• All kinds of non-kosher candies
• Margarine
• Products with sauces
• Pre-cooked products
• Sauces and mayonnaise
• Liquors and aperitives, when containing alcohol
• Wines and grape juices

The following components are always forbidden without a rabbinical supervision.

• Alcoholic beverages, vinegar, margarines (even though 100% vegetable, if not certified) products made out of meat and cheese, from grapes, albumin, animal fat, lard.
  Acidifiers: E 334, 335, 336, 337, 353, 354 (tartaric acid, tartar/argol if it is the sole acidifier of the product)
• Anti-oxidant: E 304, E 472
• Agents for surface finish: E 904, 912, 914, 920, 966
• Substitute sweetening agents, except those permitted, ie. certified
• Emulsifiers and animal gelatins: E 422, 431, 432, 433, 434, 435, 436, 445, 462, 470, 471, 472, (a, b, c, d, e or f) 473
• 474, 475, 477, 479b, 480, 481, 482, 483, 491, 492, 493, 494, 495, 570, 572, 573
• 915, also called glycerol or glycerin (mono and di-glycerides, (mono) stearate (of glycerol, of sorbitol, of calcium, of magnesium) polysorbates, sucroglycerides, gelatins (also called E 430) animal proteins.
• Powder of lactose, lactose, milk proteins, lactitol, milk byproducts, cheese byproducts, grapes sugar, grapes juice or grapes concentrated juice

Please note: it would seem useful to warn about the following components which are kosher but may be risky for the health of allergic people:

E 102, 104, 110, 122, 123, 124, 127, 131, 132, 142, 151, 161, from 210 to 219, from 221 to 228, 250, 310, 311, 320, 321.

Non-kosher coloring agents: E 120 (cochineal or carminic acid), E 163 (anthocyane)