After reading the title to this post, you might be asking yourself why anyone would sweeten their tobacco pipe. Well, the term "sweeten" doesn't mean to literally add sugar to your pipe. Instead, the term refers to the process of cleaning the sticky gunk-like buildup out of the bowl and surrounding pieces. Sweetening is an important step in maintaining a tobacco pipe, as it preserves the rich, authentic flavor and aroma of your tobacco, protecting it from the unwanted elements found in the gunky buildup.
After you've smoked a dozen or so bowls out of your pipe, you'll begin to notice a layer of black tar and resin coating the bowl. This is the direct result of small tobacco particles that vaporize (not ignite) and recondense on the side of the bowl. Small amounts of this soot substance isn't going to affect your tobacco smoke; however, large amounts that build up over the course of several months can negatively impact your smoke. The oils inside the soot begin to oxidize, creating chemical reactions that alter the flavor, aroma and other characteristics of the tobacco smoke.
Sweetening is the process of cleaning this gunk out of your tobacco pipe using an alcohol-based solution. There are literally dozens of different pipe "sweeteners" on the market, most of which contain alcohol as their primary active ingredient. When the sweetener is flushed through the tobacco pipe, it neutralizes the oxidation; thus, preserving the natural flavor of your tobacco and protecting it from unwanted changes.
But you don't have to use a special sweetener product to clean your tobacco pipe. The truth is that a high ABV spirit, such as Golden Grain or Everclear, works just as well if not better. You may have to spend a little extra for a high ABV spirit, but a full bottle will last for dozens of uses. If you're going to use a spirit to clean your tobacco pipe, choose one with minimal additives and sugar so it doesn't affect the flavor of your tobacco.
Some people also use salt in conjunction with a high ABV spirit to sweeten their tobacco pipe. The idea is that the salt works as a mild abrasive to scrub away the gunk. Experts advice pipe smokers to avoid the use of iodized salt, however, as it may create unwanted flavors in the tobacco. Use only non-iodized kosher table salt when sweetening your tobacco pipe.