Alchemy Science: Herbal Tinctures

Transcription

1 Alchemy Science: Herbal Tinctures THLady Medb ingen Echuid website: polkadotpanther.com Quick Intro A tincture is an infusion, known in modern day process engineering as solid liquid extraction or leaching. In solid liquid extraction, desired components are extracted from a solid using an appropriate solvent, as shown in the following schematic. 1 solvent, 2 extraction material (solid carrier phase with transition component), 3 transition component 4 depleted solid carrier phase, 5 solvent with dissolved transition component With a tincture, as with coffee or tea, we are interested in collecting the liquid containing the transition component following extraction. This is generally accomplished through filtration. How Extraction Works In chemistry, extraction is a separation process. A separation process can be defined as a process that uses mass transfer (the movement of mass from one location or phase to another) to convert a mixture of substances into its components. Some extractions may result in pure components, but many extractions are concerned with enriching one phase. With herbal tinctures, this means that the desired portion of the herb will be

2 extracted into the solvent (often alcohol), enriching that solvent phase with the desired herbal component. Separation occurs based on differences between physical or chemical properties of the substances in question. Properties such as size, shape, mass, density, and polarity drive mass transfer and, thus, extraction. In the case of tinctures, we are generally utilizing a difference in solubility, which arises from a difference in polarity between the two substances. What is polarity? To understand polarity, we need to take a couple steps back. Polarity is driven by electronegativity, which is affected by both atomic number and valence electrons. As we learned in basic chemistry, atoms have electrons buzzing around at different energy levels. Valence electrons are those electrons residing in the outermost shell of an atom. Valence electrons are involved in chemical bonding. An atom with a full valence shell is inert, or does not react. These are known as noble gases Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn). Helium walks into a bar. The bartender says We don t serve your kind here. He doesn t react.

3 The higher an atom s electronegativity, the more it will attract other electrons toward it. Electrons are held near an atom s nucleus by charges. In the same manner that larger magnets exert more magnetic force (magnetism depends on electrons and electric fields!), an atom with more protons and electrons will feel a stronger attractive force than one with fewer. Thus, as we increase the number of valence electrons, the negatively charged electrons are pulled more strongly toward the nucleus (filled with positively charged protons), which actually makes the atom smaller in size. For the most part, electronegativity and atomic size tend to be inversely related. Smaller atoms tend to be more electronegative than larger atoms. You may notice that electronegativity decreases as we go down on the periodic table. This is because non valence electrons act as shields between the nucleus and valence electrons. The more shielding electrons are present, the less force is felt by the outermost electrons. Now that we ve defined electronegativity, what makes a compound polar or non polar? Polarity arises from a difference in electronegativity between atoms bonded together in a compound. This separation of electric charge contributes to an electric dipole. Water is a great example of a polar molecule. Some compounds are non polar. This is because the electronegativities are balanced around the atom.

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5 In solution chemistry, there is a mantra: Like Dissolves Like. While solubility is influenced by other factors such as temperature and pressure, the overall solvation capacity of a substance is determined by its polarity. As a rule of thumb, substances with similar polarities will be more soluble than those with differing polarities. This is due to intermolecular forces. This is a whole complex topic, but for now, we can note that like with magnets a negative charge will be attracted to a positive charge on another charged molecule. Solid Liquid Extraction aka Leaching Going back to our intro, SLE or leaching is the process of extracting desired components from a solid phase by dissolving them into a liquid phase. The more soluble our desired component is with the liquid phase, the faster and more effective the process will be. Important considerations: The compound to be extracted must be soluble in the chosen solvent. The solvent should not dissolve impurities. The solvent should be non toxic. This is really important if you intend to consume your tincture or apply it to your person. The original material must be able to be removed from the solvent after extraction. With herbal tinctures, this is easily achieved through filtration. In the field of herbal tinctures, alcohol is generally a good solvent. Solubility of herbal components in alcohol varies as you may imagine, not every compound has the same polarity so some recipes may call for short extraction times while some may call for long extraction times. To really understand the time dependency of mass transfer, we need to go into differential equations, which is beyond the scope of this class. For now, we are going to focus on chemical potential and concentration gradient. Chemical Potential and Concentration Gradient Mass transfer is driven by chemical potential. Once again, we can get into calculus and advanced thermodynamics on this one, but we re keeping it simple. You may recall from basic physics that energy can be kinetic (in motion) or potential (stored). Chemical potential is a form of stored energy which can be transferred during a chemical reaction or phase transition. This concept is important in extraction because particles move from higher chemical potential to lower chemical potential. We can equate this to

6 gravitational potential, as a ball rolls down a hill from a region of higher gravitational potential to a region of lower gravitational potential. While chemical potential is influenced by many factors, we can look at it more simply by examining concentration gradient. Particles are driven from a region of high concentration and high chemical potential to a region of low concentration and low chemical potential. A higher concentration gradient, or a larger difference in concentration, will result in a higher rate of diffusion, the movement of mass from one region to another. Solubility and Surface Area Material will dissolve faster when broken up into smaller pieces. This is due to larger surface area available to interact with the solvent molecules. Think about ice melting in water and how much faster it melts when it s crushed first. So with herbal tinctures, it s a great idea to pulverize the herb using a mortar and pestle prior to extraction.

7 Summary There is a lot at work in extraction chemistry! When making an herbal tincture, the compound of interest is extracted from the solid herb through solid liquid extraction. This is facilitated by mass transfer, driven by a difference in chemical potential between the solid material and the solvent phase. The component of interest must be soluble in the solvent. Solubility is increased with higher surface area, so you should grind your herbs in a mortar and pestle before adding them to your solvent. In SCA period, they did not know all of this complex chemistry, but extractions have been carried out for ages. They knew to use a solvent that resulted in transfer of the desired component, and they knew to pulverize the material to facilitate better extraction. Practical Steps for Making Your Own Tinctures ~ Use a non toxic solvent. Alcohol is the most common, and you can use regular vodka, at least 80 proof. Tinctures can also be made using apple cider vinegar or food grade vegetable glycerine. ~ Crush your herbs with a mortar and pestle. ~ Fill a glass jar ⅓ to ½ with herbs. Add alcohol to fill the jar. ~ Store in a cool, dry place. Different herbs require different extraction times, so pay attention to your recipe. The most common extraction times are in the range of a few weeks, but ideal extraction time can vary depending on the materials. ~ Strain the herbs using a cheese cloth.

8 Bibliography 1. My education BS in Chemical Engineering from the University of Florida (summa cum laude) and MS in Chemical Engineering from UCLA 2. French, John. The Art of Distillation Web: 3. McCabe, Warren L., and Julian C. Smith. Unit Operations of Chemical Engineering. New York: McGraw Hill, Print. 4. Thermal Process Engineering: Extraction Image Sources: cloud.com/pages/p/properties of water polarity/ polar molecules.htm gradient diagram/ solutions and solubility