The latest survey conducted in 2012 found 73.4% of 163,125 restaurants and food vendors met the five conditions required to display the logo, said Pornthep Siriwanarangsun,. the department's director-general.
Those criteria cover the outlet's environment, food and taste, food storage, control of animals and insects, and food handling, he said at a seminar on Friday.
In an earlier survey, the department found 83.6% of 136,437 outlets met its quality standards. The programme began in 1999.
Dr Pornthep said common problems included food vendors' attire (such as lack of gloves or hair nets), the health of those who handle food, collection of garbage and leftover foods, and the covering of cooked foods.
The department this year introduced a new "Clean Food, Good Taste Plus" programme by selecting 74 establishments in 52 provinces, but in the end only 48 outlets from 38 provinces met the criteria.
Food centres that receive the accreditation must meet the five regular requirements and also pass six other tests.
Those standards require vendors to use serving spoons, have wash basins for customers, provide safe and accessible toilets, use organic vegetables; train staff in hygienic food preparation, and make employees wear gloves.