April 11, 2017 by Debra Lynn Dadd
While looking at a large glass jar at Oriental Trading Wedding I noticed it was labeled "not food safe" use only wrapped candy. I was under the impression that all glass was food safe. I was reading your blog and am very curious now about glass quality. Many of us store our foods in these jars.
No, not all glass is food safe. There are many types of glass used for many purposes, each with it’s own characteristics.
The most common method of making glass is to heat raw materials into a molten liquid and then rapidly cool the liquid in such a way that the atoms remain in a random state.
The raw materials are various powders which include network formers, fluxing agents, property modifiers, fining agents, and colorants.
The two most common types of glass used in consumer kitchenware are soda-lime silicate glass and borosilicate glass.
Food safe glass is regulated by the federal Food & Drug Administration (FDA). Glass (and plastic) containers containers are consider “indirect food additives" by the FDA. These are substances that may come into contact with (and end up in) food from packaging or processing equipment, but are not intended to be added directly to food.
The FDA has determined that both borosilicate glass and soda-lime silicate glass are Generally Regarded as Safe (GRAS). The GRAS designation is given to substances added to food directly or indirectly that are considered to be safe by experts.
Here is a whole study about food-grade glass, prepared by The Glass Packaging Institute: Compliance of Glass Packaging with Human and Environmental Health and Safety Toxic—in—Packaging Requirements.
This document states:
Preference for glass has persisted throughout the ages and in all cultures due in large part to its safety, impermeability, and durability. In food packaging applications, glass has long been recognized as the gold standard, due in significant part to its being virtually inert, meaning that it does not react with other elements and forms no new compounds when it comes into contact with other chemical agents or compounds. As a result of this virtually inert quality, glass does not interact with the foods or beverages contained in it, and consequently does not affect the flavor of its contents. Similarly, glass is virtually impermeable to oxygen, so does not affect -- and is indeed protective of -- the freshness of its contents. Consequently, glass does not require the addition of any food additives or preservatives in order to maintain flavor or freshness, unlike many other food packaging materials. Glass has long been recognized as the preferred material for food packaging, due to this virtually inert quality and its protection of the food or beverage that it contains.
It also states:
Unlike other packaging materials, glass packaging is manufactured at extremely high heat with simple components, resulting in oxidation of most trace amounts of heavy metals that may be present in the raw production materials [italics mine]. For this reason, and because glass packaging is virtually inert, glass packaging properly does not present any significant health and safety or environmental concerns.
Therefore even if there were any heavy metal impurities in the raw materials, they would not be present in the finished glass product.
I haven’t read the entire 50-page document so there may be more relevant information. But these are the key items for this discussion.
Soda-lime-silicate glass is made from three ingredient—sand, lime and soda ash. No lead or other heavy metals are added to this glass for any reason. Borosilicate glass is made of by adding boric oxide to the basic soda-lime-silica mix.
Lead is added to glass to make it sparkle in the light. But this is very clearly labeled with lead warnings. This is limited to “cut crystal.” And the lead WILL leach into foods and beverages. Other types of decorative glassware may also contain lead and not be so labeled because it is not intended for contact with food.
For food storage, only use glass containers intended to be used as food containers. Those will be made with a food-safe glass.
Decorative glass items are usually NOT food safe and probably contain unknown substances that can leach into food.
You can read more about lead in glassware here.