This sounds like a secret tip from grandma’s kitchen that can be surprising and useful. I’m not entirely sure which “trick” you mean, but boiling garlic in water has interesting reasons in many households.

Here are the most common reasons why grandma did it:

To soften the flavor (probably for culinary reasons):

When you boil whole garlic cloves (peeled or unpeeled) in water, their flavor changes significantly.

Less sharpness: Boiling reduces the sharp, pungent taste of raw garlic.

Sweeter flavor: The garlic develops a mild, almost sweet, buttery flavor.

Why do people do this? Garlic prepared this way is ideal for dishes where the garlic aroma is desired, but not the pungency, such as in mild sauces, spreads (hummus), or mashed potatoes. Cooked garlic can then be easily mashed into a paste.

Easier peeling:

If you need to peel a larger quantity of garlic, briefly boiling it in water (about 30 seconds to one minute) can help. The heat and moisture loosen the skin from the clove, making it much easier to peel off. However, blanching (briefly immersing it in boiling water and then in cold water) is a common method.

Home remedy (health benefits):

Garlic is known for its antibacterial and antiviral properties. Grandmothers often prepared garlic water or a garlic infusion as a home remedy.

What was it used for? Boiled garlic in water was drunk (sometimes with honey and lemon) to boost the immune system, treat colds and coughs, or lower blood pressure.

Important note: While garlic is healthy, cooking can destroy allicin, the compound responsible for most of its healing properties (it is only produced when raw garlic is crushed). A warm drink can still be soothing, however.

Plant protection (Rather unlikely in the kitchen, but possible):

Cooled water from boiled garlic is used in horticulture as a natural spray against pests (such as aphids) or fungal diseases. The strong garlic smell repels pests.

Which of these reasons motivated your grandmother? Did she want to mellow the flavor of food, make peeling garlic easier, or was she preparing a home remedy?