Summer 2025

Every year at the STAR-K Chanuka mesiba, Rav Moshe Heinemann shlit”a, STAR-K’s Rabbinic Administrator, rises to address the assembled. His annual message consists of a brief Chanuka dvar Torah, expressions of hakaras hatov to the entire staff, and a reiteration of the uncompromising principles of emes and shalom by which STAR-K is governed.

This year, he added the following to his divrei chizuk: “Good kashrus requires a clear understanding of products, process, and all the source materials that go into a certified product. What are they?

“Take nuts, for example. Hazelnuts, also known as filberts, are classical tree nuts. The bracha for all nuts grown on a tree is Borei Pri Ha’eitz.

“Peanuts, unlike their other shelled counterparts, grow in the ground. The bracha for peanuts is Borei Pri Ha’adama.

“Doughnuts,” he quipped, “are Borei Minei Mezonos. And what bracha do you make on a gallnut? None!”

“What is a gallnut? A gallnut is produced by an oak tree that has become a home to wasp eggs that have been laid on its branches. To protect itself from these unwelcome parasites, the oak tree excretes a liquid that traps the wasp eggs. The excretion hardens into a hardened sphere known as a gallnut.”

The Rav’s mention of gallnuts was both amusing and fascinating. It is worth exploring a bit further the gift and wonder of gallnuts.

The Gift of Gallnuts: Insects Doing Good

Gallnuts, also known as oak galls, are abnormal outgrowths on plant tissues, often caused by infestations from parasites. The galls are similar in appearance to warts on animals. Galls, so named from the Latin galla or “oak apple,” can vary in size, shape and color.

In most cases, insect infestation in produce creates serious kashrus issues. Fruits and vegetables that are known to be heavily infested – raspberries and Brussel sprouts for example (though there are others) – may not be eaten at all, since checking such produce and eliminating the pests is virtually impossible. But when certain insects infest trees and other plants, they can create the conditions to allow for the formation of gallnuts.

Gallnuts are not edible but have value as a significant source of tannic acid. Tannic acid accumulates in the galls as a defensive mechanism and has a plethora of uses in both food and non-food applications.

Tannins: The Hidden Miracle in Gallnuts

Tannins are incredibly versatile. The Gemara mentions mei afatzim – gallnut juice – as the base raw material used to manufacture iron gall ink. The “juice,” or gallnut extract (gallo-tannin) is the tannic acid extracted from the gallnuts. The tannic acid reacts with iron salts to create a dark, permanent ink and can be used as a bonding agent for dyes. The technical term for this dye fixative is a mordant.

Aside from its use as a key component in developing mordants, tannic acid is also used as an insecticide, as well as in the vegetable tanning of leather and the production of red wines. It plays an important role in alcohol production as a colorant. It is the tannin in the oak cask staves that color aging whiskey from clear to amber. Tannic acid is also used to clarify beverages.

The versatility of tannic acid in the food and health industries is quite remarkable. My first tannic acid experience was when Mallinckrodt, a global manufacturer of specialty food additives and pharmaceutical products, requested – at Pepsi Cola’s behest – kosher certification for tannic acid to be used as an additive to Pepsi beverages.

Today, the study of tannic acid has led to the development of many new pharmaceutical and biomedical applications. It has multiple uses in medicine and medical research due to its antimicrobial, antioxidant and anti-inflammatory properties. It has also displayed antiviral and antifungal activity and been found to impart anti-inflammatory, antibacterial and anticancer activity to materials.[1] All told, tannic acid is proving to be an increasingly valuable industrial workhorse.

When in Egypt…

In 1904, Dr. Edward G. Acheson, the inventor of silicon carbide (an abrasive used in grindstone), prepared an interesting treatise on the production of bricks in Mitzrayim and hypothesized what it was about the straw and stubble mixture that made them so durable. He noted that the only known historical reference to the use of organic material added to clay is the use of straw mixed with clay described in the Torah[2] in Sefer Shmos.[3] According to his hypothesis, the presence of gall atonic acid in the stubble that was added to the clay contributed to the clay’s elasticity. The extracted tannins in the stubble made all the difference.

He theorized, “This explains why the straw was used and why the children of Israel were successful in substituting stubble for straw, a course that would hardly be possible were the fibre of the straw depended upon as a bond feasible for the clay, but quite reasonable where the extract of the plant was used.”[4] Dr. Acheson’s fascinating statement furthers our understanding of the remarkable utility of gallnuts and provides us with a new appreciation of events in the Torah.

A Halachic Irony

The halachic irony of gallnuts is that in most circumstances of insect interaction with its host, it is the insect that secretes various liquids on its host. Examples include aphids and cicadas that secrete honeydew – a sugary liquid waste – as they feed on plant sap, and lac insects (Kerria lacca) that secrete lac – a natural resin – used to produce resinous glaze.

But in the case of gallnuts, it is the tree that secretes a protective excretion to protect itself from insect predators, which – through the niflaos Haboreh – creates the nut that isn’t.

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[1] A. Baldwin, B.W. Booth, “Biomedical Applications of Tannic Acid,” abstract, Journal of Biomaterials Applications, 2022;36(8):1503-1523, https://journals.sagepub.com/doi/10.1177/08853282211058099.

[2] Edward G. Acheson (1904) “Egyptianized Clay” in Transactions of the American Ceramic Society. pp. 31–65, excerpted in Wikipedia article, “Tannic Acid.”

[3] Shmos 1:14, “… with clay and with bricks”; 5:7, “… let them go and gather stubble for themselves,”; 5:11, “… go take for yourselves stubble from wherever you find it.”

[4] Acheson, loc. cit.