Chemicals for craft distilling

Distilling chemistry starts before the still. In the mash tun, the enzymes that convert starch to fermentable sugar, and the yeast that follows, each work best in a narrow pH range. Distillers bring the mash down with a food-grade acid such as phosphoric acid 75% USP food grade or citric acid monohydrate USP food grade, and bring it up with potassium bicarbonate FCC/USP when it runs too acidic. Fruit washes often get sodium metabisulfite food grade as an antioxidant to slow oxidation and browning.

The rest of the shelf is for the equipment. Clean-in-place (CIP) cycles on fermenters, lines and heat exchangers use a caustic wash, usually sodium hydroxide, to lift organic soil, then an acid rinse to remove mineral scale. Copper pot stills get a citric acid wash between runs. Glycerin USP appears in some finished products for mouthfeel, within TTB limits on blending materials. Match the grade to where the chemical ends up: in the spirit, or rinsed off the steel.

Grade tells you what else comes in the drum. A food-grade or USP acid is made and tested to a monograph that limits lead, arsenic and other impurities; a technical-grade acid is not held to those limits. FCC phosphoric acid, for example, is limited for arsenic, fluoride and lead, which wet-process technical acid can carry in larger amounts.

Glycerin is the clearest case. The USP monograph includes limits for diethylene glycol and ethylene glycol, two toxic contaminants that have turned up in glycerin from poorly controlled sources. Use glycerin USP for anything that goes into a spirit, never technical glycerin. For CIP, technical-grade caustic and acids are normal because they are rinsed out, so the final rinse is what protects the next batch.

The Alcohol and Tobacco Tax and Trade Bureau (TTB) regulates distilled spirits plants under 27 CFR Part 19, including records of materials received and used in production. Labeling, and what may be added to a spirit after distillation, falls under 27 CFR Part 5: harmless blending materials such as glycerin are limited, and some additions need formula approval before the product can be labeled. Check before you add anything to finished spirit.

FDA rules in 21 CFR cover the additives themselves. Phosphoric and citric acids are generally recognized as safe (GRAS), and FCC or USP grade documents their purity. Labels must declare sulfites when the finished product contains 10 ppm or more of sulfur dioxide. OSHA's Hazard Communication Standard requires an SDS on hand for every hazardous chemical, including 50% caustic and concentrated acids.

• Technical salts in mash water. Calcium chloride for brewing water has to be food grade. A technical-grade bag is for de-icing and dust control.
• Mixing up hydrate forms. Anhydrous citric acid delivers about 9% more acid per pound than monohydrate, so a straight swap overshoots the target pH.
• Dosing by recipe, not by meter. Phosphoric acid 85% carries more acid per gallon than 75%. Measure pH after each addition, whichever strength you buy.
• Too much sulfite in fruit washes. Sulfur dioxide is volatile and can carry into the distillate as a struck-match note.
• Non-food carbon for polishing. Carbon used to filter spirits should be sold for food or beverage use, with low extractable metals.