This is a nice basic/general overview of the modern column still distillation process for American whiskey. I didn't want to get too technical...so here goes:
We get truck loads of corn, rye, wheat, malted barley in and we put those grains in silos. Depending on the recipe of the whiskey we are going to make, we grind up the grains and weigh them to the correct % of each grain and then that grain is added to the cooker along with water and some of the set back from the previous run (this is also called the “sour mash process…it’s the liquid that is left after the alcohol is all distilled out.) The cooking process is done to release all the starches from the corn, rye, or wheat.
For example: for making bourbon, corn is added first, then the rye and then the malted barley is added last. Malted barley is very important. “malted” means that it actually sprouts and starts growing a plant. When it does that it releases enzymes to feed that plant. When the malted barley is added to the cook, those enzymes immediately turn those starches in to sugar. The next process is fermentation, and since yeast can not feed on starch…the malted barley turns those starches in to eatable sugars for the yeast.
After the mash is cooked and the barley has been added to turn those starches in to sugars, it is pumped over to a fermenter which is a simply a large stainless steel tub, and yeast is added. Yeast are single celled organisms that are just like people going to a Las Vegas buffet because all they want to do is eat. As they eat, they belch out cO2 and piss alcohol, and they give off heat all during this feeding frenzy. After about 3 days of non-stop eating, the yeast die off and that sweet mash that started out originally with all that sugar, now kind of tastes like a stale beer (and a little sour) and we have a low alcohol “distillers beer”.
That distillers beer is fed 3/4 of the way up to the column still, and steam is coming up from the bottom of that first distillation in that column still (also called a beer still) under 212 degrees. Since alcohol vaporizes at a lower temperature than water the alcohol rises out of the top of the still, and cold water tubes surround that pipe of alcohol vapors and that condenses that vapor back in to liquid, and that is what comes off the first tail box (also called a Trybox). This still just raised the alcohol content from low proof alcohol, into a higher proof, usually around 125 proof or so, depending on the distillery and the product. This is a pretty clean product, but it has a bit too many fusel oils (bad stuff that gives ya a headache) so it needs one more distillation to be cleaned up and a little better.
The grains and liquid that is left over from the first distillation are separated, and the liquid is added to the next cook, and fermenters to help the PH levels and helps give a consistent flavor profile from mash to mash. The alcohol is sent to a second still that is not a column still since it is only liquid and no grains, and it is a sort of hybrid pot still called a “doubler” (since this is the second distillation). After it is distilled a second time it comes off around 135 proof, and is very clean and less oily.
We send that distillate up to the FILL HOUSE to a retention tank, since we can’t enter bourbon/rye/wheat whiskey at more than 125 proof in the barrel, we add water to that product to bring it down from the 135 to 125 proof in that retention tank, and then it is entered in to the barrels and the barrels are put up in the rickhouses for aging for 4+ years in most cases. To be called "straight" the whiskey must be aged for a minimum of 2 years.