granite countertops

How Clean Are Your Marble and Granite Countertops?

The food safety and desirability of natural stone countertops comes across as fact in many articles you might find online, and countertop companies claim this as well. However, you cannot believe everything you read online, and countertop companies have a stake in making this claim. How do you know that marble and granite are actually safe for use as kitchen countertops?

A study carried out for the Hospitality Institute of Technology and Management in 2006 sought to find out. It made a comparison of the level of cleanliness that four popular stone materials could attain with ordinary cleaning products. Below is a discussion of that study.


The study compared four types of kitchen countertops: local granite, granite from Brazil, Carrara white marble, and Cambria Snowdon quartz. The basis for looking at the two types of granite selected was the frequency and amount of natural pitting present on the surface. All of the natural stones had a polished finish, but none received treatment with a sealer or impregnator. The study did not specify the finish for the quartz stone.


The author designed a test to measure the amount of cross-contamination with a pathogenic material typically found in many types of food. He cultured a lab-sourced nonpathogenic version of E. coli, a bacterium frequently found in food which may cause health problems when ingested.
The author spread one ml of the cultured bacteria on each of the kitchen countertop materials, and then allowed to dry for a quarter of an hour. This duplicated the typical way that bacteria from food preparation can contaminate kitchen countertops. For example, if you cut meat on the countertop, some of the blood or tissue may land on the surface.

The author prepared two stainless steel bowls and ordinary dishcloths to clean the surface. One bowl contained 2 liters of clean water at room temperature. The other bowl contained 5 ml of Dawn dish detergent diluted in 2 liters of ordinary water. Cleaning the countertops involved dipping the dishcloth in the detergent solution and rubbing the contaminated surface 10 times in one direction. The author then rinsed the dishcloth in the detergent solution and rubbed the area 10 times, this time in the opposite direction. After this, the author collected a sample of the surface microorganisms by rubbing a Hydra-Sponge on the surface for 30 seconds.

The author then took another dishcloth, dipped it in plain water, and rinsed the area. He then collected a sample using another Hydra-Sponge. To disinfect the surface, the author sprayed it with a solution of 0.5% white vinegar, leaving it to dry for 35 minutes before collecting another sponge of microorganisms.

The author tagged each sponge and placed in an incubator for 24 hours. At this point, the author counted the number of microorganisms of E. coli still present in the sponges.


According to the study, results showed that washing the surface with ordinary dish soap reduced the number of microorganisms to nearly the level of sanitation required by the Food and Drug Administration for kitchen countertops. Rinsing the washed areas with ordinary water further reduced these numbers to significantly lower levels than the FDA requirements. Sanitizing the surfaces with the 0.5%, white vinegar solution brought the levels down to zero, with the exception of the granite from Brazil, which did not show any significant changes in microorganism level.


The study indicates that granite, marble, and quartz are particularly suited for use as kitchen countertops. Because they are very easy to clean. Ordinary dish soap and water were enough to bring bacterial contamination levels to very safe levels for all the samples, and sanitizing with a very weak acid eliminated all signs of the contamination in all but the granite from Brazil.

The study also suggests that there is no reason to buy special cleaning products to keep granite and marble countertops clean. These products will probably serve other purposes, such as polishing and sealing natural stones. But, they are not necessary for maintaining the food safety of these kitchen countertops.

The study used room temperature water to wash and rinse the surfaces. It would be interesting to see if warm water would have reduced the count even more, perhaps to the point that sanitation would no longer be necessary.
It is important to note that the natural stones exhibited some pitting and did not benefit from a protective seal. This means that even though natural stones may be porous, they are not porous enough to harbor bacterial growth.
It is also important to note that you should not use of any type of acid on marble, even the very weak solution used in this test. If you want to sanitize marble to bacteria levels to zero, you can use isopropyl alcohol.


Many people have avoided natural stones such as granite and marble for their kitchen countertops. Because they believed the porosity made it a breeding ground for bacteria. This study scientifically proves that natural stones are just as easy to keep clean and food safe as quartz countertops using ordinary household cleaners.

With that in mind, it is a good time to consider granite and marble for your kitchen countertops. You should get in touch with a reputable countertop specialist in your area. KNC Granite has a large array of food-safe granite and marble slabs from which to choose. You can check actual slabs at our showroom in Lanham, Maryland.

We do not only supply top-quality granite stones, however. We are experts at fabricating and installing kitchen counters or bathroom vanities. Also we specialize in kitchen remodeling and bathroom upgrade projects, delivering on time and on budget.

Aside from natural stones, we carry some of the top brands of engineered stone, including Cambria, Caesarstone, Silestone, and MSI, all of which come with manufacturer warranties.

Give us a call or email us for your free in-home consultation and quote.

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