How does cold brew tea bags work?

Cold brew tea bags work by holding tea leaves inside a fine mesh or fabric pouch while the pouch sits in cold water for several hours, so the water pulls flavor and color out of the leaf without any leaf escaping into the drink. When the steep is done you lift the bag out, and what stays behind is tea you can pour straight from the jar or pitcher.

The bag is doing two jobs at once: it is the steeping vessel and the strainer. That is why the material and the mesh opening matter more than the shape, and why a bag sized for a 64 oz jar behaves differently from a small sachet dropped into a mug.

What happens inside the bag during a cold steep

Cold water moves slowly into the leaf. Heat normally opens leaf cells quickly, but at refrigerator or room temperature the water has to work its way in, so the compounds that give tea its color and body come out over hours rather than minutes. The bag walls let water pass freely while holding the leaf in place, which is the whole point of the pouch.

Makers describe the steep in their own terms. BIMYJ, whose reusable cotton bags appear in Best Cold Brew Coffee Filters for Mason Jars and Pitchers, tells buyers to fill the bag with coarse grounds, steep in liquid 12 to 24 hours, then remove it. The same window applies to tea leaf: the bag stays in until the liquid tastes strong enough, then comes out.

Because the leaf stays contained, you never pour the brew through a second filter. The bag is removed, the liquid is already clear of leaf, and the jar goes back in the fridge. That single step is the difference between cold brew tea and tea you brew hot and then chill.

Cotton, mesh and paper bags behave differently

The pouch material sets how much solid matter reaches the liquid. Cotton and fine synthetic mesh hold leaf and dust while letting water and dissolved flavor through. Doppeltree sells a reusable cotton bag measuring 12 x 12 in, and the maker states that cotton lets natural oils pass through where paper would hold them back. For tea, that means more of the leaf’s aromatic character ends up in the cup.

Disposable bags trade reusability for convenience. HRX Package lists a 6 x 10 in non-woven bag with a cotton drawstring, and the maker states the fine mesh lets water saturate grounds whether coarse, medium or fine. The same construction works for loose tea, and the maker lists loose tea among the bag’s uses.

Metal is the third option. HAVORNYX makes a 304 stainless steel filter sized for a 64 oz wide mouth Mason jar, with a published size of 8.27 x 3.15 in, and the maker states the fine mesh supports steeping so you can make cold brew concentrate in about 12 hours or overnight. A steel basket holds its shape, so leaf sits in a defined column rather than settling into a soft pouch.

Matching the bag to the jar or pitcher

Bag size decides how much leaf you can steep at once and whether the pouch stays submerged. A bag that is too large for the vessel folds over itself and traps leaf in dry pockets. A bag that is too small leaves the water under leafed and the brew thin.

Published dimensions give you something to check against your vessel. The Doppeltree bag is 12 x 12 in. The BIMYJ bag is listed at 7.9 x 11.8 in, though the maker’s own text describes it as 11.8 x 11.8 in and says it fits 1 to 1.5 cups of grounds, so the two figures in that listing do not agree. The HRX Package bag is 6 x 10 in and the maker states it suits 64 oz Mason jars or 1 gallon pitchers. bellamei lists a 22 x 26 in nylon mesh bag, sized for brewing vessels rather than jars.

If you would rather not handle a loose bag, a pitcher with a built-in filter does the same job. The cold brew makers in Best Cold Brew Coffee Makers for a Grit Free Pour pair a vessel with a removable filter. JunVpic publishes a 100 micron stainless weave, QHH publishes a 160 micron weave, and County Line Kitchen describes a stainless steel mesh filter in a 64 oz wide mouth Mason jar. Takeya lists a 2 qt Tritan pitcher, and Primula lists a 1.6 qt glass carafe that the maker states makes up to 6 cups (52 ounces).

Leaf, water and time

Cold water extracts less bitterness than hot water, so you can use more leaf than you would for a hot steep without the cup turning harsh. Start with about one tablespoon of leaf per cup of cold water, put it in the bag, and let it sit in the refrigerator. Taste at the 6 hour mark and again at 12; pull the bag when the flavor is where you want it.

Makers publish steep windows rather than tea ratios. BIMYJ states 12 to 24 hours. HAVORNYX states about 12 hours or overnight for cold brew concentrate. Those windows are for coffee, but the chemistry of cold extraction is the same, and tea leaf usually gives up its flavor faster than coarse coffee grounds, so check earlier rather than later.

Water temperature matters less than time, but it does shift the result. A refrigerator steep is slower and cleaner tasting. A countertop steep runs faster and pulls more color. Either way the bag comes out before serving, and the brewed tea keeps in the refrigerator for a few days.

Removing the bag and cleaning up

Lifting the bag out is the whole harvest. Let it drain over the vessel for a moment, then dump the leaf. Reusable cotton and mesh bags need a rinse in cold water and a full air dry before the next batch, and Doppeltree states its bag should be hand washed between uses to preserve the cotton fibers. BIMYJ states its bags are machine washable and reusable for 100 or more brews.

Steel filters rinse clean and can go in the dishwasher. HAVORNYX states its strainer has a smooth stainless surface that rinses clean and is dishwasher safe. If you brew in a pitcher with a built-in filter, the filter lifts out the same way and the vessel goes in the dishwasher where the maker says it is safe.

Storage is the last piece. Dry bags keep better in a drawer than in a heap on the counter, and the trays in Best Tea Bag Drawer Trays for a Shallow Kitchen Drawer are sized for that. iDesign lists a 6.5 x 9.5 x 2.25 in clear organizer with 6 compartments, Dicunoy lists a 10 x 6.5 x 2.5 in bamboo box with 6 sections, and MinBoo lists 13.98 x 10.83 x 2.17 in with 7 adjustable slots.

If you would rather steep loose leaf in a pot and chill it, a glass pot with a removable infuser works on the same principle. HIWARE lists a 33 oz borosilicate pot, PARACITY lists an 18.6 oz pot, Teabloom lists a 27 oz pot, DOPUDO lists a 40 oz pot, and Ehugos lists a 1500ml pot, all with removable stainless infusers, as covered in Best Glass Tea Brewing Pots for Loose Leaf Tea. The infuser comes out, the tea goes in the fridge, and the result is cold brewed tea without a bag.