The Chemistry: Why Hot Tea Gets "Shocked"
When you pour boiling tea over ice, the rapid drop in temperature causes a chemical reaction called "Cream Down" or "Tea Cream."
At high temperatures (100°C), caffeine and catechins (tannins) are highly soluble and dissolve happily together. However, when the temperature plummets instantly, these molecules are no longer soluble. They bind together and precipitate out of the liquid, forming microscopic solids. This is why your iced tea looks muddy or opaque. It also locks the bitterness into the liquid, forcing you to add syrup to mask the taste.
The Extraction Difference: Tannins vs. Amino Acids
Tea flavor comes from a balance of three main components: Catechins (bitter/astringent), Caffeine (bitter), and Amino Acids (sweet/savory). Temperature affects each of these differently.
Research confirms that cold water is excellent at extracting Amino Acids (like L-Theanine) but is very poor at dissolving tannins. This creates a beverage that is naturally sweet without any sugar.
| Compound | Hot Brew Extraction | Cold Brew Extraction |
|---|---|---|
| Tannins (Bitterness) | High (Rapid release) | Very Low (Remains in leaf) |
| Caffeine | 100% Extraction | ~50% Extraction |
| L-Theanine (Sweetness) | Often degraded by heat | Preserved & Highlighted |
| Antioxidants | High (but unstable) | High (and heat-stable) |
The Antioxidant Surprise
You might assume hot water extracts more "good stuff," but studies show the opposite for Green Tea. Cold brewing preserves delicate flavonoids that are otherwise destroyed by boiling water. One study found that cold-brewed green tea actually harbored more polyphenols than its hot counterpart.
How to Make the Perfect Cold Brew
The beauty of cold brew is that it is impossible to "burn" the leaves. It is the most forgiving method of making tea, but it requires patience.
- Ratio: Use 10g of loose leaf tea (approx 2 tablespoons) per 1 Liter of cold water.
- Vessel: Put leaves in a pitcher or glass bottle. Fill with filtered cold water.
- Wait: Place in the fridge.
- Green / White Tea: 4 to 6 Hours.
- Oolong / Black Tea: 8 to 12 Hours (Overnight is best).
- Strain: Pour through a sieve into a clean glass.
Safety Warning: Never Make "Sun Tea"
A popular 90s trend was to leave a jar of tea in the sun to brew. Do not do this. The sun heats the water to around 55°C (130°F), which is the perfect breeding ground for bacteria like Alcaligenes viscolactis. Cold brewing in the fridge (at 4°C) keeps the tea out of the bacterial "danger zone".
Which Teas Work Best?
While any tea can be cold brewed, some shine brighter than others.
- Tie Guan Yin (Iron Goddess): This Oolong turns into pure floral nectar when cold brewed. It tastes like orchids and honey.
- Silver Needle White Tea: Becomes incredibly refreshing, like cucumber water with a melon finish.
- Japanese Sencha: The "Umami" savory notes pop, making it a very sophisticated, broth-like refresher.