Your First Hot Process Soap Recipe
Hot process uses the same beginner-friendly oil blend as our first cold process recipe — but instead of waiting for saponification to finish in the mold, you cook the batter in a slow cooker until the reaction completes. The payoff: soap that’s safe to use much sooner, with a charming rustic look.
The Recipe (2 lbs of oils)
- Olive oil: 16 oz (454 g) — 50%
- Coconut oil: 9.6 oz (272 g) — 30%
- Shea butter: 6.4 oz (181 g) — 20%
- Sodium hydroxide (lye): 4.5 oz (128 g)
- Distilled water: 9.5 oz (270 g) — a touch more water than cold process, since some evaporates during the cook
- Fragrance oil (optional): up to 1.3 oz (36 g) — add after the cook
Superfat: 5% • Yield: about 10 bars (4 oz each)
Same lye math as cold process: identical oils, identical lye. The only difference is what happens after trace.
Equipment
- Digital scale (weigh everything — no volume measuring)
- Slow cooker (4+ quart) dedicated to soap making
- Stick blender dedicated to soap making
- Two heat-safe pitchers (lye solution + oils) — stainless steel or heavy plastic, never aluminum
- Thermometer (infrared or probe)
- Standard silicone loaf mold
- Chemical-splash goggles, nitrile gloves, long sleeves
- Spatula and a lid for the slow cooker
Step by Step
- Gear up. Goggles, gloves, long sleeves, ventilated area.
- Make the lye solution. Weigh the distilled water, slowly stir in the weighed lye (lye into water, never the reverse). Set aside.
- Melt the oils directly in the slow cooker on low. Coconut oil and shea butter first; once melted, stir in the olive oil.
- Cool both to 100–130°F, then pour the lye solution into the oils in the slow cooker.
- Stick-blend to trace — short bursts, stirring between, until the batter thickens to thin-pudding consistency.
- Cook on low with the lid on for 45–60 minutes, stirring every 10–15 minutes. The batter will go through stages: it may bubble up like a volcano (stir it down), then turn waxy and translucent, like vaseline or mashed potatoes.
- Test for doneness. The batter looks uniformly waxy/translucent with no liquid oil pooling, and a small cooled sample doesn’t “zap” on the tongue (or reads pH 8–10 on a strip). When in doubt, cook 15 minutes more.
- Turn off the heat. Add fragrance now (if using) — post-cook addition means the scent survives better. Stir well; work quickly, the batter stiffens as it cools.
- Glop into the mold. Hot process batter is thick — spoon it in and press down firmly to avoid air pockets.
- Cool 24 hours, unmold, and cut.
- Cure at least 2 weeks — technically safe now, but a short cure still improves hardness and lather. Stand bars on edge with airflow.
Beginner Tips
- Don’t walk away during the cook. The volcano stage is dramatic but harmless if you’re there to stir it down.
- Add fragrance after the cook, not before. Heat and active lye eat delicate scents.
- Work fast once it’s done cooking. Have your mold ready before you turn off the cooker.
- Expect rustic. Hot process will never give you glass-smooth tops. Lean into the handmade look.
- Same lye rules apply: weigh twice, goggles on, lye into water.
Free Tools for This Recipe
- Lye Calculator — verify the lye amount for these oils.
- Soap Mold Calculator — size your mold to the batch.
- Soap Fragrance Calculator — fragrance amounts for hot process.
- Soap Cure Date Calculator — mark your 2-week ready date.
