(1) Be careful of wood vinegar derived from an unspecified wood type. During charcoal product testing, charcoal products are classified by wood type. Products that are not derived from a safe tree type and undefined products are not permitted to be treated as charcoal. Similarly, the wood type used as a raw material in wood vinegar products must be clearly defined.
There are many trees that are poisonous or potentially poisonous to humans and animals, such as the camphor tree and Japanese andromeda (ericaceae evergreen tree with poisonous leaves). In recent years, the preparation of wood vinegar has spread across Southeast Asia and, with Brazilian produced pulverized coal, in Chili as well. It is becoming increasingly important, therefore, to check the safety of the wood type used for extracting the wood vinegar in foreign countries as well as Japan. In South America, for example, there is a tree containing the deadly poison curare, which is used as an arrow toxin. The types of trees which contain such poison differ according to region.
(2) Wood vinegar derived from construction scratch wood ----- When building material or other dismantled material is used as raw material, the wood vinegar acquired from that material is a decomposition product of fibrin, far from an actual tree. Moreover, when the material contains paint, pesticides, metal objects such as nails and staples, and metal other than iron, the end product contains substances harmful to humans, animals and farm products.
(3) Wood vinegar extracted at high temperatures ----- Wood vinegar extracted at high temperatures is often black in color with oil floating on the surface. In particular, 3.4 benzpyrene is detected at 425‹C or higher. Caution, therefore, is required.
(4) When the wood vinegar container or extraction device is not comprised of an acid resistant material ----- The areas of the extraction device, storage tank and containers which come in contact with the wood vinegar must be comprised of an acid resistant material, such as synthetic resin. When a drum can is used, for example, not only does the metal melt causing the wood vinegar to darken, but the zinc and other heavy metals also melt, making the wood vinegar unsuitable for agricultural use. Even with stainless steel products, the possibility that the iron and other metals will melt into the product does exists. Any stainless steel products employed must conform to the high quality defined in the Japanese Industrial Standard SUS.304 (otherwise referred to as 18-8-Production).
(1) Wood vinegar that contains foreign elements or appears dirty when a small amount is placed in a glass container is poor quality. A good quality product has a clear yellowish-brown to reddish-brown tone. The color should be similar to the pleasing hue of black tea, beer or wine.
(2) The wood vinegar should not have an offensive odor. Wood vinegar that has a strong, pungent odor is a synthetic product containing a substance such as glacial acetic acid to adjust the pH.
(3) The pH value should be around 3. Higher extraction temperatures result in higher acidic values.
(4) The specific gravity of wood vinegar should be around 1.015 at a liquid temperature of 15‹C (when Japanese oak is carbonized in an earthen kiln). Wood vinegar extracted at higher temperatures has a higher specific gravity. Please note that the specific gravity varies greatly when a device other than an earthen kiln, such as an iron kiln or combustion furnace, is used.
(5) You can also identify good wood vinegar using chemicals. The wood vinegar is acceptable if the liquid remains transparent at the neutral point, and if the odor remains the same as the initial odor without abnormalities. The chemical test must prove that the liquid is the cell fluid (sap) of a young tree.
(1) Type of Wood
Broad-leaved trees such as Japanese oak, beech and white oak are considered good raw material. However, Quercus acutissima, a broad-leaved tree as well, has a low component concentration.
Second to broad-leaved trees, pine, cedar, hinoki cypress, Japanese larch and bamboo are often employed in farm products. Of these, the component concentration in pine is rather high.
Different woods have different component ratios. For example, acetic acid - a representative component of wood vinegar - is found in broad-leaved trees in quantities of 3.5-4.0% compared to 1.4% in bamboo.
(2) Extraction Temperature
The duration of extraction is limited to the period in which white smoke is emitted, and does not include the period of initial smoke. Thus, extraction should begin when the temperature of the charcoal (earthen) kiln exhaust port is 80-84‹C and end when the temperature is 110-120‹C. If the smoke turns blue, the substance turns into fibrin-decomposed tar, thereby deteriorating the germicidal effect of the product.
(3) Immediately after extraction, a chemical reaction (polymerization) continues to take place with the wood vinegar components. Thus, the substance should be allowed to stand for a period of 3-6 months until the components settle.
Characteristics such as color (including transparency), pH and specific gravity are important factors in the quality assessment of wood vinegar. Recent years have seen the introduction into the market of various imported wood vinegar products and similar products made using special production methods. It is important, therefore, that you acquire wood vinegar from a producer you can trust.
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