I’ll explain this the best way I know how, but as I understand it, some people have a set way of doing things, and others may do it another way. You MUST throw away the first certain percentage of every run. This is the methanol, ie. wood alcohol, that can lead to blindness if taken in a high enough doses. Most books and experts say about 2-4 ounces per 5 gallons of wash. The methanol starts to boil off at 148 degrees. The good stuff you want is the ethanol, which starts to boil off and turn into steam at 173 degrees. Some books say you can tell by a oily touch if you rub some between your finger and thumb, and may have acetone smell like finger nail polish. The heads come from somewhere between 173 to 200 degrees, real specific right. Some say the hearts, come between 180 -205 degrees. Then the tails come through somewhere between 190-211. They say the tails have a musty, wet cardboard smell, and will have an oily film on the top. Most every still will have its own sweet spot, which will be slightly different from every other still. A pot still will give off a lower proof product with a higher finished flavor. This you want of distilling a product like whiskey or a brandy. A reflux still will give off a higher alcohol level with not much flavor. You want this if you are distilling a product like gin or vodka. There are probably a hundred or more different types of stills, made mostly of copper or stainless steel. You need some copper if you are running a stainless steel still. This helped to cleans the sulfur out of the finished product. Everyone’s tastes are different in what they like in a alcohol drink..some like the different flavors, some like the higher alcohol flavors. So if you were hypothetically to run a still, especially if you are new to it, it’s best to collect the foreshots (the bad stuff) first in a small jar and throw it out. Then collect everything in small jars and number them as the come off. After the run is over, do some sampling with the nose, and the tongue. When you find the tastes you like, (usually in the middle numbers) you keep those, the hearts. Some like to add a bit of the heads and the tails to the hearts. It’s entirely up to your taste, but be warned, it’s the side chemicals in the heads and tails that give you the hangovers and other problems. So after you keep what you want, you can then pour what you don’t want to drink and put them into a container and add that back into the still when you are hypothetically running your next batch, since the heads and tails still have recyclable alcohol. So, to be exact, it’s up to your own taste as to what you want to keep, then you recycle what you don’t want. I hope this answers your question.