Boiling the sugar if not using potasium metabisulphit is required to kill any bacteria and wild yeast that may be in the sugar and water. Yes hot water will kill the yeast, also to much sugar will will do same. Most of these hillbilly recipes call for 3 cup of sugar wich is usually to much. It should be closer to 2 cup.
1 more thing everyone is going to say not to use the milk jug to use glass or better bottle that is NPT1 plastic. Buy a generic 1 gal bottle of apple juice from Kroger or Wal-Mart. Ive discovered that these are NPT1 plastic. But will fall in floor when racking if you dont watch them. Tried using 1 gal. plastic bottle 1 time. Never again. But to not spend a bunch of money they will work. And adding a little sugar the juice can be used to make wine. Juice is less than $4.00.
I found it really hard to find glass 1 gallon jugs. Everything is plastic now-a-days
However: I did find three sources: My local Health Food store had organic applejuice (which ended up as an absolutely awesome apple wine btw), My local liquor store had gallon glass jugs of wine, and my local self-recycle area had a great selection..
Go to your local spring water supply company where they fill the 5 gallon jugs to load on trucks, go in there and ask if they have any 5 gallon glass bottles for sale, If your lucky they have a few laying around. The last time I got one was about 15 years ago and I got it for $20. Then go on ebay and get a rubber stopper and air lock for about $3. This setup works really well for making wine or what ever else you want to ferment just remember to leave headspace in the jug to allow for the foam head. You don't want to use any milk jugs because there's no real way to sanitize them and there is a chance there is still lacto virus in the jug from the milk. If you get a lacto virus infection in your wine it will turn into a big glob of gelatin like snot that will hardly even pour out of the jug and stink Like sour milk . Your always better to use good clean glass or go out and buy a new HDPE fermenter bucket with a lid, You can get a kit already made up for this at your local brew shop.
Yeast is a type of fungus or mold. It is a living thing. When you buy dry active yeast, it is nothing more than a dried up powdered fungus that reproduces it's self when it has a nice warm place and food to eat. Sugar is it's main food source and it also needs moisture to reproduce so when you mix some fermentable sugar like cane, corn or fruit sugar with some warm water and add powdered yeast the dry yeast absorbs the water and wakes up and then starts eating the sugar for food to reproduce it's self. The yeast uses enzymes to metabolize the sugar into proteins and then uses theses proteins to make more yeast cells when this happens the yeast produce waist, This waist is alcohol and carbon dioxide. The yeast will eat as much sugar as it can until there is no more sugar left to eat or until there is so much alcohol in the water that it poisons the yeast so that it either dies off or goes dormant and falls to the bottom of the container. This is how beer, wine and other alcoholic drinks are made. There are probably more than a thousand different breeds of yeast that produce alcohol. as long as the yeast has a warm place, moisture and food it will do it's job of making alcohol. If it gets too cold it will go dormant and if it gets too hot it will die, keep it in the middle and it makes alcohol.