Lye has to dissolve in a liquid before it can meet the oils. That mix is the lye solution, often called lye water. The Lye Calculator tells you how much liquid to use, and the liquid can be more than plain water.

Safety reminder: whatever the liquid, add lye to the liquid slowly, never the other way around, and wear goggles and gloves. See Lye Safety.

Water

Distilled water is the standard. It has no minerals or other extras to react with the lye, so results are predictable from batch to batch.

How much liquid?

Set it in the Lye Calculator as water % of oils, lye concentration, or a water:lye ratio. The Lye Calculator page explains how they compare. Using less water than the full amount is called a water discount.

Other liquids you can use

Swap all or part of the water for the same weight of another liquid. Keep the total liquid weight the same as the calculator says.

Milk (goat, cow, buttermilk)

• How soapers handle it: Freeze it into cubes first. Set the container in an ice bath and add lye a spoonful at a time, stirring, so it stays cool (about 50–65°F).

• Watch for: Milk sugars scorch and turn orange or brown if they get hot, and the soap can smell. Keep the soap cool after pouring. Soap Queen refrigerates or freezes the poured soap to stop gel phase.

Coconut milk

• How soapers handle it: Same as milk: freeze it and add lye slowly.

• Watch for: Extra sugars heat up and can crack the top.

Beer or wine

• How soapers handle it: Let it go flat, then boil it to drive off the carbonation and alcohol. Cool it completely, or freeze it, before adding lye.

• Watch for: Fizz and alcohol can foam up or bubble over. Boil extra, because some of it evaporates.

Coffee or tea

• How soapers handle it: Brew it strong, chill it, then add lye slowly.

• Watch for: It darkens the soap. Coffee grounds can be used as an exfoliant (see Additives).

Aloe vera juice

• How soapers handle it: Freeze it, then add lye slowly in an ice bath.

• Watch for: Its sugars can scorch like milk.

Fruit and vegetable juices

• How soapers handle it: Freeze to a slush and add lye slowly. One author (Kelly Cable) finds juice works for about a quarter of the water before it browns or overheats.

• Watch for: Sugars scorch and heat the loaf, and most juices turn soap brown. Lemon and lime juice contain citric acid, which uses up lye. Your superfat ends up higher than you set unless the recipe accounts for it.

Keep sugary lye solutions cold. NOAA's chemical data warn that sodium hydroxide heated with sugars above about 183°F (84°C) can give off carbon monoxide. Milk, juice and sweet drinks all carry sugars, so use the ice bath and work where air moves.

Holding some liquid back: some soapers dissolve the lye in part of the water and add the milk or drink to the oils, or at trace. This makes the lye solution you mix stronger than the recipe's setting. Keep at least three-quarters of the water with the lye, and never try to dissolve lye with no water at all.

Additives that go in the lye water

A few additives are dissolved in the lye solution. Details are on the Additives page. - Sodium lactate: stir into lye water that has cooled to 130°F or below. - Sugar: dissolve it in warm lye water. - Salt: dissolve it in hot lye water. - Silk fibers: dissolve them in hot lye water.

KOH (liquid soap)

Potassium hydroxide works the same way but makes a soft soap paste that's diluted later. Use the KOH setting in the Lye Calculator, and handle KOH with the same care as NaOH.

Sources - Soap Queen: How to Add Lye to Milk for Cold Process Soap (freeze milk, ice bath, about 50–65°F, scorching). https://soapqueen.com/magicpod/add-lye-milk-cold-process-soap/ - Soap Queen: How to Use Alcoholic Beverages in Cold Process Soap. https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/how-to-use-alcoholic-beverages-in-cold-process-soap/ - Soap Queen: Soapy Mess-Up Quick Guide (milk and coconut milk sugars cause cracking; cool temperatures). https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/soapy-mess-quick-guide/ - Soap Queen: How to Use Sodium Lactate (cooled lye water, 130°F or below). https://soapqueen.com/bath-and-body-tutorials/sunday-night-spotlight-sodium-lactate/ - Lovin Soap Studio: Soapmaking Additive Chart (sugar, salt and silk in lye solution). https://lovinsoap.com/soapmaking-additive-chart/ - Soapformulator: Beer, wine, coffee, tea and juice in soap (juice at about 1/4 of water per Kelly Cable; citric acid in lemon/lime juice; NOAA warning on sugars and hot lye above 84°C; holding liquid back raises lye concentration). https://soapformulator.com/learn/liquids-in-soap - Soapmaking Forum: Aloe vera juice (freeze it, add lye slowly in an ice bath). https://www.soapmakingforum.com/threads/aloe-vera-juice.71617/ - NOAA CAMEO Chemicals: Sodium hydroxide solution reactivity profile. https://cameochemicals.noaa.gov/chemical/1499