Probably not. Perishable food and drinks are considered unsafe after being in the danger zone (40°F - 140°F, 5°C - 60°C) for more than 4 hours (EDIT: when I was a cook in Massachusetts, four hours was the cut off. Apparently the USDA recommends two hours). And note: that's a cumulative four hours over the course of the foodstuff's lifetime, not four hours in a row. If the milk sits on the counter for an hour, then it's boiled and put into tea which then sits out for three hours, it's considered unsafe.
Leaving food out too long at room temperature can cause bacteria (such
as Staphylococcus aureus, Salmonella Enteritidis, Escherichia coli
*O157:H7*, and Campylobacter) to grow to dangerous levels that can cause
illness. Bacteria grow most rapidly in the range of temperatures
between 40 °F and 140 °F, doubling in number in as little as 20
minutes. This range of temperatures is often called the "Danger Zone."
Keep Food Out of the "Danger Zone"
Never leave food out of
refrigeration over 2 hours. If the temperature is above 90 °F, food
should not be left out more than 1 hour. Keep hot food hot — at or
above 140 °F. Place cooked food in chafing dishes, preheated steam
tables, warming trays, and/or slow cookers. Keep cold food cold — at
or below 40 °F. Place food in containers on ice.
Also crucial to remember when food safety is concerned: FAT TOM. FAT TOM is a mnemonic device which stands for:
- Food
- Acidity
- Time
- Temperature
- Oxygen
- Moisture
All of those things are a factor in the growth of bacteria. With room-temperature milky tea that's been sitting out all day, we've got the full gamut:
- Nutrients from the milk (food)
- If it's milky tea, it you probably didn't put lemon in it, because let's face it, that'd be gross unless you have a thing for curdled milk.
- Time - you said it's been there since this morning
- Temperature - at room temperature
- Oxygen - I doubt this is space tea or that it was stored in a vacuum.
- Moisture - it's a cup of infused water and milk. Doesn't get much more moist than that.
Remember: When in doubt, throw it out.
Hmmm.....
Well, I've lived in India for 12 yrs & this is how I make 'masala chai' or 'spiced milk tea' at home & in my restaurant-
2 cups water
1 teaspoon black tea, loose leaf (I use Tokla tea from Nepal)
1 tablespoon grated fresh ginger
10 black peppercorns, coarsely ground
500 ml full fat 'whole' milk
Sugar to taste
In a stainless steel 3L pot combine tea, water, ginger & black pepper, bring to boil over high heat. Allow to boil for about 2 minutes.
Add milk to boiling tea, again allow to come to a boil. (Watch the pot closely in case the milk begins to foam, if it does foam- stir & decrease heat a little) Allow to simmer uncovered for 6 minutes.
Remove from heat, let stand for 2 minutes. Add sugar to taste if desired & stir. Use a tea strainer to strain into cups to serve. (or serve sugar on the side so people can add sugar to their own tastes)
Some notes-
I think you are trying to make 'tulsi' chai?
Tulsi = Indian holy basil
If so usually the fresh tulsi leaves (around 8-10) are added to the boiling tea mixture with around 8 green cardamoms, 2 cloves, 1/4 tsp fennel seeds, and a pinch of cumin seeds as I recall. Some Indians dry roast the whole spices to mellow the flavor a bit.
Use spices like fennel, cloves, star anise, cumin sparingly as their strong flavors can take over & give the chai a 'mouthwash' taste which isn't pleasant.
Best Answer
If you want to prevent the milk from curdling when adding ginger, you have to boil the ginger or at least add it to boiling milk.
Ginger protease (the curdling agent in fresh ginger) is rapidly destroyed at temperatures above 70°C. It does not matter if the milk has been boiled in advance if you add ginger to cold or room-tempered milk, it will still curdle.