{"id":40,"date":"2026-03-16T18:52:50","date_gmt":"2026-03-16T17:52:50","guid":{"rendered":"http:\/\/www.7virides.com\/cs\/suroviny\/chemie-saponifikace\/"},"modified":"2026-03-25T11:19:31","modified_gmt":"2026-03-25T10:19:31","slug":"chemie-saponifikace","status":"publish","type":"page","link":"https:\/\/www.7virides.com\/en\/suroviny\/chemie-saponifikace\/","title":{"rendered":"Saponification Chemistry: Why Soap Forms and How It Works"},"content":{"rendered":"<blockquote>\n<p><strong>TL;DR:<\/strong> Soap is formed by a chemical reaction between oil and lye: the fatty acids in the oil determine all the properties of the finished soap (hardness, lather, conditioning), which is explained by their chain length and saturation. The correct calculation of the saponification number is essential for a functional soap.<\/p>\n<\/blockquote>\n<p>Soap is created by a chemical reaction. You know that. But why do different oils give different soap? Why does coconut oil make hard soap with a big lather and olive oil make soft soap with a silky lather? Why does soap need to age? And why does fresh soap burn the skin but ripe soap does not?<\/p>\n<p>The answers are in the chemistry of fatty acids - and they are surprisingly easy to understand. This site explains the chemistry of soap without academic jargon. You'll need basic high school chemistry, nothing more.<\/p>\n<h2 id=\"co-jsou-mastne-kyseliny-a-proc-na-nich-zalezi\">What are fatty acids and why do they matter?<\/h2>\n<p>Fatty acid is the chemical building block of fats - without understanding fatty acids, it is impossible to understand what is hidden in oil. Fats and oils are <strong>triglycerides<\/strong> - molecules composed of glycerol (a three-carbon alcohol) and three fatty acid chains. The glycerol is always the same. The fatty acids vary - and it is their properties that determine what kind of soap is made from a given fat.<\/p>\n<p>Fatty acid has two parts:<\/p>\n<ul>\n<li><strong>Carboxyl group<\/strong> (-COOH) at one end: this part reacts with sodium hydroxide during saponification<\/li>\n<li><strong>Hydrocarbon chain<\/strong> at the other end: its length and saturation determine its properties<\/li>\n<\/ul>\n<h3 id=\"jake-je-rozdeleni-mastnych-kyselin-podle-delky-retezce\">How are fatty acids classified by chain length?<\/h3>\n<p>Fatty acids vary in length from 8 carbons (caprylic acid) to 22+ carbons (erucic acid). Length affects:<\/p>\n<ul>\n<li><strong>Shorter chains (C8-C12):<\/strong> Faster water soluble, better cleaning ability, more foam. Example: lauric acid (C12) in coconut oil.<\/li>\n<li><strong>Medium chains (C14-C18):<\/strong> Balance between cleaning power and conditioning. Example: palmitic acid (C16) and stearic acid (C18).<\/li>\n<li><strong>Long chains (C18+):<\/strong> Conditioning, gentle but less cleansing. Example: oleic acid (C18:1) in olive oil.<\/li>\n<\/ul>\n<h3 id=\"jak-se-lisi-nasyceni-mastnych-kyselin\">How does fatty acid saturation differ?<\/h3>\n<p><strong>Saturated fatty acids<\/strong> have only single bonds in the chain (-C-C-). They are:<\/p>\n<ul>\n<li>Room temperature solids (coconut fat, butter, tallow)<\/li>\n<li>Chemically stable - do not oxidize easily<\/li>\n<li>In soap: hard, stable, long-lasting<\/li>\n<\/ul>\n<p><strong>Unsaturated fatty acids<\/strong> have one or more double bonds (-C=C-). They are:<\/p>\n<ul>\n<li>Liquid at room temperature (olive oil, sunflower oil, hemp oil)<\/li>\n<li>Less stable - subject to oxidation (which is why olive soap can turn yellow)<\/li>\n<li>In soap: softer, conditioning, but softer and less durable<\/li>\n<\/ul>\n<p><strong>Monounsaturated (one double bond):<\/strong> oleic acid (C18:1) - olive, avocado, rapeseed oil.<\/p>\n<p><strong>Polyunsaturated (multiple double bonds):<\/strong> linoleic acid (C18:2) - sunflower, hemp, evening primrose oil. Alpha-linolenic acid (C18:3) - linseed oil.<\/p>\n<h2 id=\"jak-probiha-saponifikace-chemicka-reakce-krok-za-krokem\">How does saponification work: the chemical reaction step by step?<\/h2>\n<p>Saponification is the hydrolysis of fat in an alkaline environment - the breaking down of fats with lye. Simply put:<\/p>\n<pre><code>Fat + NaOH \u2192 Soap + Glycerin\n<\/code><\/pre>\n<p>More precisely:<\/p>\n<pre><code>Triglyceride + 3 NaOH \u2192 3 Soap salts + Glycerol\n<\/code><\/pre>\n<h3 id=\"co-se-deje-na-molekularni-urovni\">What happens at the molecular level?<\/h3>\n<p>The hydroxide ion (OH-) from NaOH attacks the ester bond in the triglyceride - the bond between the glycerol and the fatty acid. This bond is cleaved (hydrolysis). It is released:<\/p>\n<ol>\n<li><strong>Glycerol<\/strong> (glycerin) - a new free molecule<\/li>\n<li><strong>Anion fatty acids<\/strong> (carboxylate) - immediately traps the sodium ion Na\u207a to form <strong>sodium soap salts<\/strong><\/li>\n<\/ol>\n<p>This reaction is <strong>Exothermic<\/strong> - releases heat. This is why the lye solution heats up during preparation and why the soap heats up in the mold after pouring.<\/p>\n<h3 id=\"co-je-saponifikacni-cislo-a-jak-se-pouziva\">What is the saponification number and how is it used?<\/h3>\n<p>Saponification number (SAP) is a practical constant - each fat has a specific SAP number for NaOH, expressing how many grams of NaOH are needed to saponify 1 gram of fat. This number results directly from the molecular weight of the fatty acids in the fat.<\/p>\n<p><strong>Examples of SAP values (NaOH):<\/strong><\/p>\n<table>\n<thead>\n<tr>\n<th>Oil\/Fat<\/th>\n<th>SAP (NaOH)<\/th>\n<th>Main fatty acid<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Coconut oil<\/td>\n<td>0,178<\/td>\n<td>Laurick\u00e1 (C12)<\/td>\n<\/tr>\n<tr>\n<td>Palm kernel oil<\/td>\n<td>0,178<\/td>\n<td>Laurick\u00e1 (C12)<\/td>\n<\/tr>\n<tr>\n<td>Beef tallow<\/td>\n<td>0,140<\/td>\n<td>Palmitic + Stearic + Oil<\/td>\n<\/tr>\n<tr>\n<td>Cocoa butter<\/td>\n<td>0,137<\/td>\n<td>Stearic + Palmitic<\/td>\n<\/tr>\n<tr>\n<td>Olive oil<\/td>\n<td>0,134<\/td>\n<td>Oil (C18:1)<\/td>\n<\/tr>\n<tr>\n<td>Sunflower oil<\/td>\n<td>0,134<\/td>\n<td>Linoleic (C18:2) + Oleic<\/td>\n<\/tr>\n<tr>\n<td>Avocado oil<\/td>\n<td>0,133<\/td>\n<td>Oil<\/td>\n<\/tr>\n<tr>\n<td>Shea butter<\/td>\n<td>0,128<\/td>\n<td>Stearicka + Olejov\u00e1<\/td>\n<\/tr>\n<tr>\n<td>Castor oil<\/td>\n<td>0,128<\/td>\n<td>Ricinol (C18:1-OH)<\/td>\n<\/tr>\n<tr>\n<td>Linseed oil<\/td>\n<td>0,135<\/td>\n<td>Alpha-linolenic (C18:3)<\/td>\n<\/tr>\n<tr>\n<td>Hemp oil<\/td>\n<td>0,135<\/td>\n<td>Linoleic + Alpha-linolenic<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Coconut oil has a higher SAP (0.178) than olive oil (0.134) because lauric acid (C12) has a shorter chain and lower molecular weight - there are more molecules per gram of fat, each needing one NaOH.<\/p>\n<h2 id=\"jak-mastne-kyseliny-ovlivnuji-vysledne-mydlo\">How do fatty acids affect the finished soap?<\/h2>\n<p>Each fatty acid in the fat contributes to the specific properties of the soap - this is a key table for understanding recipes.<\/p>\n<h3 id=\"kyselina-laurova-c120-v-kokosu-palmojadrovem\">Lauric acid (C12:0) \u2014 in coconut, palm kernel<\/h3>\n<p><strong>Soap properties:<\/strong> Hardness, large bubbles, strong cleaning power, fast solidification. <strong>The problem with excess:<\/strong> Drying. Above 40% in the recipe, the soap begins to irritate the skin.<\/p>\n<h3 id=\"kyselina-myristova-c140-v-kokosu-palmojadrovem-muskatovem\">Myristic acid (C14:0) \u2014 in coconut, palm kernel, nutmeg<\/h3>\n<p><strong>Soap properties:<\/strong> Hardness, foaminess. Supplements lauric acid. <strong>Combination with laurel:<\/strong> Together they form the characteristic cleansing base of coconut soap.<\/p>\n<h3 id=\"kyselina-palmiticka-c160-v-palmovem-oleji-loji-kakaovem-masle\">Palmitic acid (C16:0) \u2014 in palm oil, tallow, cocoa butter<\/h3>\n<p><strong>Soap properties:<\/strong> Hardness, durability, creamy foam (unlike lauric - large bubbles). Does not hold. Stable, long-lasting soap. <strong>Why tallow is good:<\/strong> The combination of palmitic + stearic creates a hard, durable soap with an excellent creamy lather.<\/p>\n<h3 id=\"kyselina-stearova-c180-v-loji-kakaovem-masle-sea-masle\">Stearic acid (C18:0) \u2014 in tallow, cocoa butter, shea butter<\/h3>\n<p><strong>Soap properties:<\/strong> Extra hardness, conditioning, creamy foam. The most stable saturated acid in soap. <strong>Specific feature:<\/strong> Sodium stearate is a solid white substance - the base of solid soap.<\/p>\n<h3 id=\"kyselina-olejova-c181-v-olivovem-avokadovem-repkovem-mandlovem\">Oleic acid (C18:1) \u2014 in olive, avocado, rapeseed, almond<\/h3>\n<p><strong>Soap properties:<\/strong> Conditioning, soft silky foam, softer soap. Slow trace. <strong>Specific feature:<\/strong> Soaps with a high oleic acid content are soft and silky, but require a long curing time (see Castilian soap).<\/p>\n<h3 id=\"kyselina-linolova-c182-ve-slunecnicovem-konopnem-pupalkovem\">Linoleic acid (C18:2) \u2014 in sunflower, hemp, evening primrose<\/h3>\n<p><strong>Soap properties:<\/strong> Conditioning, lightness on the skin, anti-inflammatory effect (anecdotal). Shorter shelf life due to oxidation. <strong>Dosage:<\/strong> Keep below 15% for good soap durability.<\/p>\n<h3 id=\"kyselina-ricinolova-c181-oh-v-ricinovy-oleji\">Ricinoleic acid (C18:1-OH) \u2014 in castor oil<\/h3>\n<p><strong>Soap properties:<\/strong> Thick, stable foam, conditioning. The only unsaturated acid capable of forming a dense foam on its own (hydroxy group). <strong>Dosage:<\/strong> 5-10% in the recipe. More causes too soft soap.<\/p>\n<h2 id=\"proc-mydlo-zpenuje-hydrofilni-a-lipofilni-konec\">Why soap lathers: hydrophilic and lipophilic ends<\/h2>\n<p>Soap has two faces - it is a molecule with a dual nature. The soap molecule (sodium salt of a fatty acid) has two completely different ends:<\/p>\n<p><strong>Hydrophilic end<\/strong> (water lover): carboxylate group (-COO-Na\u207a) - negatively charged, attracts polar water molecules.<\/p>\n<p><strong>Lipophilic end<\/strong> (fat lover): hydrocarbon chain - non-polar, attracts fats and oils.<\/p>\n<p>This amphiphilic (two-bone) structure is the basis of the detergent effect. What happens during washing:<\/p>\n<ol>\n<li>In the presence of water, soap molecules arrange themselves into <strong>micel<\/strong> - spherical structures where the lipophilic ends point inwards and the hydrophilic ends point outwards into the water.<\/li>\n<li>In the centre of the micelle, fat and dirt molecules are \"packed\" - the lipophilic ends trap them.<\/li>\n<li>Micelle is water soluble due to its hydrophilic surface - it washes off with water.<\/li>\n<li>Dirt goes away with the water.<\/li>\n<\/ol>\n<p>The foam is just a visual byproduct - the bubbles themselves clean minimally. The micelles do the cleaning job. That's why there are effective soaps with little lather (Castile soap in hard water) and ineffective ones with a lot of lather.<\/p>\n<h2 id=\"jake-je-ph-mydla-a-proc-na-tom-zalezi\">What is the pH of soap and why does it matter?<\/h2>\n<p>Alkalinity is a natural part of the process - but fresh soap is more alkaline than mature. Fresh soap has a pH of 11-13. Ripe soap has a pH of 9-10. Healthy human skin has a pH of 4.5-5.5.<\/p>\n<p>How it works: the soap is alkaline and the alkalinity disrupts the skin's &#8222;acid mantle&amp;#8220the natural acidic environment of the skin surface that protects against pathogens. After washing with soap, the skin needs 30-90 minutes to restore the skin's pH. The source of normalization is sebum and sweat with an acidic reaction.<\/p>\n<p><strong>Why doesn't homemade soap scratch like industrial soap?<\/strong> Two reasons:<\/p>\n<ol>\n<li><strong>Glycerin.<\/strong> Glycerin remains in homemade soap - it is removed in most industrial soap (sold to cosmetics). Glycerin is a humectant - it holds moisture in the skin and compensates for the alkaline effect.<\/li>\n<\/ol>\n<ol>\n<li><strong>Super fat.<\/strong> Unsaponified oils in homemade soap (5-10% super fat) leave a thin conditioning film.<\/li>\n<\/ol>\n<p><strong>How to test the pH of mature soap:<\/strong><\/p>\n<ul>\n<li>pH papers (10-14 range): wet a ripe piece of soap, attach the paper<\/li>\n<li>Phenolphthaleins (drop test): red = free hydroxide (immature or corrosive), colourless = fine<\/li>\n<li>&#8222;Zap test&#8220;: touch the tip of your tongue to the soap - prick like a battery = free hydroxide<\/li>\n<\/ul>\n<h2 id=\"co-se-meni-behem-zrani\">What changes during curing?<\/h2>\n<p>Aging is not just waiting - soap changes physically and chemically. <strong>Water evaporation:<\/strong> Fresh soap contains 30-40% water. After 4 weeks, it's 20-25%. After 8 weeks, 15-20%. This water has to go - the soap is then harder, more durable and the lather is better.<\/p>\n<p><strong>Crystallization of soap salts:<\/strong> Soap molecules arrange themselves into a more stable crystalline structure. This change improves the soap physically - denser soap bars are easier to hold and last longer.<\/p>\n<p><strong>pH drop:<\/strong> The alkalinity in the first days comes partly from free NaOH, which has not yet had time to react. By continuous reaction with CO\u2082 from the air (formation of soda ash) and the completion of saponification, the pH decreases.<\/p>\n<p><strong>Oxidation of unsaturated fatty acids:<\/strong> On the contrary, an unfavourable process - double bonds in unsaturated acids (oleic, linoleic) can react with oxygen to form peroxides and aldehydes - this is rancidity. Therefore, soaps with a high percentage of olive, hemp or linseed oil have a shorter shelf life and should be protected from direct sun and heat.<\/p>\n<h2 id=\"proc-se-mydla-lisi-srovnani-vlastnosti\">Why soaps differ: properties comparison<\/h2>\n<table>\n<thead>\n<tr>\n<th>Property<\/th>\n<th>Low (oils for this property.)<\/th>\n<th>High (oils for this property.)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td><strong>Hardness<\/strong><\/td>\n<td>Olive, sunflower<\/td>\n<td>Coconut, tallow, palm butter, cocoa<\/td>\n<\/tr>\n<tr>\n<td><strong>Foam (large bubbles)<\/strong><\/td>\n<td>Olive, tallow<\/td>\n<td>Coconut, palm kernel<\/td>\n<\/tr>\n<tr>\n<td><strong>Foam (cream)<\/strong><\/td>\n<td>Coconut (big bubbles, not creamy)<\/td>\n<td>Tallow, palm, cocoa, shea<\/td>\n<\/tr>\n<tr>\n<td><strong>Conditioning<\/strong><\/td>\n<td>Coconut (purifies)<\/td>\n<td>Olive, avocado, rapeseed, castor<\/td>\n<\/tr>\n<tr>\n<td><strong>Shelf life<\/strong><\/td>\n<td>Hemp, flax (oxidizes)<\/td>\n<td>Tallow, coconut, palm (stable)<\/td>\n<\/tr>\n<tr>\n<td><strong>Subtlety<\/strong><\/td>\n<td>Coconut in high %<\/td>\n<td>Olive, avocado, goat's milk<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><em>Want to dive deeper? Kevin Dunn, \"Scientific Soapmaking&#8220; (2010) - the most detailed scientific book on homemade soapmaking, accessible even without a chemistry background.<\/em><\/p>\n<h2 id=\"caste-otazky\">Frequently asked questions<\/h2>\n<p><strong>Which fatty acid is most important in soap?<\/strong> Lauric acid (C12) - forms hardness and foam. Without it (without coconut oil) the soap will be soft and weakly foaming. It is the basis of any functional recipe.<\/p>\n<p><strong>What happens if I use the wrong saponification number?<\/strong> Too little NaOH = soft, non-functional, possibly greasy soap. Too much = caustic soap that burns the skin. Always use a calculator.<\/p>\n<p><strong>Why does my soap oxidize and turn rancid?<\/strong> Unsaturated fatty acids (olive, linseed, hemp oil) break down in the presence of oxygen. Protect soap from sun and heat, add antioxidants (vitamin E, ROE).<\/p>\n<p><strong>Is 100% olive oil soap really functional?<\/strong> Yes, but it requires 6-12 months to mature. The so-called Castilian soap is soft but becomes hard and soft after maturing. It's not a first-class recipe for beginners.<\/p>\n<p><strong>Why does coconut soap dry and how to solve it?<\/strong> Lauric acid is a strong cleaning agent - alta 40% is aggressive. Solution: reduce coconut to 25-30% and increase super fat to 8-10%.<\/p>\n<p><strong>What oil should replace palm oil?<\/strong> Combination: coconut (25-30%) + cocoa butter (10-15%) + castor oil (8%). This gives you hardness, lather and conditioning without the palm tree.<\/p>\n<p><strong>See also:<\/strong><\/p>\n<ul>\n<li><a href=\"\/en\/soap-making-ingredients\/soap-making-oils-encyclopedia\/\">Oil and fat encyclopedia<\/a> - SAP values and profiles of all oils<\/li>\n<li><a href=\"\/en\/soap-making-ingredients\/soap-calculator\/\">Soap calculator<\/a> - how to use SAP values in practice<\/li>\n<li><a href=\"\/en\/soap\/what-is-cold-process-soap\/\">What is cold process<\/a> - practical guide to production<\/li>\n<\/ul>","protected":false},"excerpt":{"rendered":"<p>TL;DR: M\u00fddlo vznik\u00e1 chemickou reakc\u00ed mezi olejem a louhem: mastn\u00e9 kyseliny v oleji ur\u010duj\u00ed v\u0161echny vlastnosti hotov\u00e9ho m\u00fddla (tvrdost, p\u011bnu, [&hellip;]<\/p>\n","protected":false},"author":0,"featured_media":0,"parent":16,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"class_list":["post-40","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/pages\/40","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/types\/page"}],"replies":[{"embeddable":true,"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/comments?post=40"}],"version-history":[{"count":1,"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/pages\/40\/revisions"}],"predecessor-version":[{"id":180,"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/pages\/40\/revisions\/180"}],"up":[{"embeddable":true,"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/pages\/16"}],"wp:attachment":[{"href":"https:\/\/www.7virides.com\/en\/wp-json\/wp\/v2\/media?parent=40"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}