More than once is nicely put, they're doing it all the time.
1 Food safety incidents in 2003
1.1 Poisonous Jinhua ham
2 Food safety incidents in 2004
2.1 Counterfeit baby formula
2.2 Adulterated pickled vegetables
2.3 Counterfeit alcoholic drinks
2.4 Soy sauce made from human hair
3 Food safety incidents in 2005
3.1 Sudan I red dye
4 Food safety incidents in 2006
4.1 Counterfeit drugs
4.2 School food poisoning
4.3 Contaminated turbot fish
4.4 Pesticide residue on vegetables
4.5 Infected snail meat
4.6 Poisonous mushrooms
5 Food safety incidents in 2007
5.1 Counterfeit drugs
5.2 Alleged carcinogen used in frying oil
5.3 Contaminated wheat gluten and rice protein used for export
5.4 Sewage used in tofu manufacturing
5.5 Cardboard bun hoax
6 Food safety incidents in 2008
6.1 Tainted Chinese dumplings
6.2 Contaminated powdered ginger
6.3 Contaminated baby formula
6.4 Contaminated egg products
7 Food safety incidents in 2009
7.1 Plastic tapioca pearls
7.2 Pesticide in mantou
7.3 Fake lamb meat
7.4 Formaldehyde-laced blood pudding
8 Food safety incidents in 2010
8.1 Gutter oil
8.2 Dyed green beans
9 Food safety incidents in 2011
9.1 Adulterated noodles
10 Food safety incidents in 2012
10.1 Contaminated strawberries
11 Food safety incidents in 2013
11.1 Pork Meat Scandal
11.2 Lamb Meat Scandal
11.3 Recycled Out-of-date food
11.4 Fake Beef
11.5 Cat Meat Scandal
12 Food safety incidents in 2014
12.1 Gutter oil scandal
12.2 Expired meat sold to global brands
13 Food safety incidents in 2015
13.1 Sodium Formaldehyde Sulfoxylate (CH3NaO3S)
13.2 Fake hot pot soup
en.wikipedia.org/wiki/Food_safety_incidents_in_China