Coffee grounds (used, dried)

David Fisher, The Complete Photo Guide to Soap Making (Creative Publishing International, 2018), p. 19: exfoliants, "Start with 1 to 2 teaspoons per 1 pound (454 g) of oils or soap base"; calendula petals "retain their yellow color nicely"; coffee grounds, "scrubbiness is determined by the coffee’s grind"; "Citrus peel (dried and ground): offers a medium scrub; add at trace"; cornmeal, "medium scrub; premix with oil and add at trace"; eucalyptus leaves, "a medium scrub, especially if not very finely ground"; lavender buds "will turn brown in cold process soap and look like mouse droppings; gently grind them first to avoid this"; loofah, "light to medium scrub"; mint is "prone to bleeding; steep as a tea first"; oatmeal, "like coffee, the scrubbiness is determined by how ground it is"; poppy seeds, "light to medium scrub"; pumice, "heavy-duty scrub; great for mechanic’s or gardener’s hand soaps"; rose hips, "medium to high scrub; also adds natural color"; rose petals "turn black in cold process soap"; sandalwood powder "gives a medium to high scrub, and makes a lovely purple color"; "ground stone fruit pits (apricots, peaches) and berry seeds (ground or whole) give a medium to high scrub factor"; walnut shells, "a nice medium scrub and a lovely medium brown color".

Anne-Marie Faiola, Pure Soapmaking (Storey Publishing, 2016): "1 teaspoon of sodium lactate for every 16 ounces (1 pound) of oils or 0.5 percent" (the two disagree: a teaspoon of the 60 % solution a pound is about 1.45 % of the oils, so neither is taken from this book); salt at "½ teaspoon per pound of oil", added to the water before the lye; "Salt decreases lather significantly"; salt bars are 80–100 % coconut oil at a high superfat. Chapter 5: coffee grounds, "For extra scrubbing power, use a coarse grind, while for gentle exfoliation, a super-fine espresso grind is best. Use the grounds to make coffee before adding them, or they might bleed brown halos into the final soap"; "Adding colloidal oatmeal can accelerate trace in your soap recipe; premixing with water can help avoid this"; honey, "start soaping with lye-water and oils both under 100°F (38°C). Add the honey at trace ... Once the soap is finished, place it in the refrigerator or freezer immediately to prevent overheating". Chapter 7: "A half teaspoon of sugar per pound of soap added to your lye-water can help your bar lather up."

Soap Queen, tea and coffee in soap: brewed coffee at about half the water; "Coffee turns green when the lye is added, then morphs into brown"; grounds "about 1 teaspoon per pound of soap", added at trace; "Dry grounds can bleed in the soap".

Lovin Soap, soapmaking additive chart: clay 1 teaspoon, oatmeal, coffee grounds and cocoa 1 tablespoon per pound of oils; cocoa into the warm oils; silk, "1 pea size pinch per pound of soapmaking oils".

Anne-Marie Faiola, Pure Soapmaking (Storey Publishing, 2016), recipes in chapters 8–10. 100% Castile-Brine Stamped Cube: "1 tablespoon sea salt" dissolved in the water before the lye, for 33 oz of olive oil. Oatmeal Soap for Babies: "2 teaspoons bentonite clay dispersed into 4 tablespoons distilled water" and "2 tablespoons colloidal oatmeal" at thin trace, for 15.1 oz of oils whose olive oil is infused with "2 tablespoons Egyptian chamomile" in a teabag in 14.5 oz of oil, 2 hours in a double boiler. Nettle & Yarrow Upcycle: "2 teaspoons dried yarrow powder dispersed into 1 tablespoon apricot kernel oil" in one of two halves of 24.1 oz of oils. Buttermilk Honeycombs: "3 tablespoons honey" at thin trace for 25.1 oz of oils. Banana Cream Pie Layered Bars: "1.2 ounces banana, 1.5 ounces whipping cream, and 1.5 ounces water, pureed" at thin trace for 35.2 oz of oils, then the freezer "for 24 hours to avoid overheating from the sugars in the banana". Annatto-Yarrow with Embeds: "1 tablespoon spirulina powder" and "1 teaspoon yarrow powder", added "directly to the hot lye-water", for 7.1 oz of oils; "2 tablespoons poppy seeds" in one of two halves of 34 oz of oils. Cucumber Layers: "1 ounce cucumber puree" into the whole batch at thin trace, 22 oz of oils. Gardener Scrub with Coffee Grounds: 50 oz of oils, the batter divided "into four exactly equal sections", one each for "5 teaspoons paprika", "5 teaspoons ground orange peel dispersed into 1 tablespoon of canola oil", "5 teaspoons brewed coffee grounds" and "10 teaspoons green zeolite clay". Indigo-Annatto Negative-Space Funnel Pour: "1.5 tablespoons indigo powder" whisked into the lye-water and "1 tablespoon alkanet root powder dispersed into 1 ounce sunflower oil" at very thin trace, 35.2 oz of oils; "In order to bring out the best color for the indigo powder, the soap must go through a hot gel phase". Black Tea Funnel Pour: 5.5 oz of brewed black tea added at thin trace, 5.5 oz of water for the lye, 33.1 oz of oils. Goat Milk Sunset Burst: "0.7 ounce goat milk powder dissolved in 1 ounce distilled water" for 17.1 oz of oils and "1 ounce goat milk powder" for 25.2 oz, added at trace: "To help avoid scorching, this recipe incorporates the goat milk by using a concentrated solution of powdered goat milk."

Spent coffee grounds, Scientific Reports 11 (2021): moist grounds "favour the proliferation of micro-organisms".

L. M. Sousa and M. C. Ferreira, "Spent coffee grounds as a renewable source of energy", Particuology (2019), Table 1: dried grounds, loose bulk density 0.38–0.39 g/mL, tapped 0.46–0.47.