The freshness of ingredients is important, particularly for LME. Fresh LME has a bit more fresh malt aroma than DME, but the latter has a better shelf life. Liquid extract typically has a maximum shelf life of about two years, depending on storage conditions; cooler is better. Liquid extract will darken and develop off-flavors like licorice, molasses, and ink aromas from Maillard reactions as it ages. Oxidation of the fatty acid compounds in old LME can cause blunt, stale, or soapy flavors. These oxidation off-flavors from old extract are collectively known as “extract twang.” Some homebrewers complain that they can’t make good beer with LME, but it’s just a matter of freshness. Check the “use by” dates on the cans (within six months is generally best), or buy from a shop that has a high turnover of stock. Dry malt extract has a better shelf life (five years) than the liquid, because the extra dehydration slows the chemical reactions. If you can’t get fresh LME, use DME.
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An all-extract brewer will be quite satisfied brewing entirely from beer kits as long as they follow the guidelines in this book.