Malt is cereal grain that has been allowed to start to germinate by moistening it and keeping it warm and happy, then using hot air to cut off the process. This malting process helps to develop the enzymes needed to convert the starches in the grain to sugars so the yeast can ferment them. The germinated grain is then roasted to different degrees, giving different
flavours from sweet to dark fruit to chocolate to strong coffee—think of different beers from Pilsner to Stout. Some grain is given a special malting/roasting precess to produce speciality grains. Crystal malts are given a steam treatment to convert starches to sugars and can be used for flavouring, body, and head retention. Other grains my be de-bittered for colouring with less bitter/roasted flavour. There is an ever growing catalogue of speciality grains.
Malts can be divided into to basic categories: Base Malt, the bulk of the malt used, has a high diastatic power (lots of enzymes so they can easily convert the starches). Speciality Malt, can be roasted from light to dark or may have been given some “special” treatment and usually have low or no diastatic power. Speciality malts are used for their colour, flavour, or aromatic qualities. Generally, the majority of the grist (the grains for the beer) is made up the base malt with different speciality roasted grains to make up the different flavours and colours of beer. That’s not to say that great beer can’t be made from a single grain (ask the Czechs about their Pilsner), but the majority of beer have more then just a base grain.
Grains are rated for their sugar potential (“gravity points”), colour, diastatic power, nitrogen content, moisture, etc… Most of these ratings are not needed by the average home brewer. The gravity potential and colour is the meat of the stats and is usually all thats needed to know. Beyond that, unless you’re a professional brewer, it won’t really matter to your beer.
Gravity Points are tallied in specific gravity, a measure of density of a liquid. This rating is based on a laboratory measured potential of a pound of grain mashed to produce a gallon (US) of wort. For example, one pound of Pale 2-Row Malt mashed to produce a gallon of wort will yield a gravity of 1.038 where pure water has a gravity of 1.000. Now, that’s in a lab. In the real world the mash system efficiency will be 60-85% (typical). If we assume 65% efficiency then the yield in a gallon would be 1.025 (1.038 reduced to 38: 38×65%=24.7 or 1.0247).
Colour rating for a grain is usually given in Degrees Lovibond, Standard Reference Method (SRM), or European Brewery Convention (EBC). In North America Lovibond or SRM (they are approximately equal) are typically used, but EBC does appear at times. The measurement of the beer colour is done placing the beer in a clear cylinder (specific diameter varies between the standard used, but is defined for that standard) and making scientific measurement of colour. For grains, the rating is the approximation of the resulting beer after mashing based on laboratory conditions.
Once all the hard work is done in taking the sugars from the malt, the end result is called “Sweet Wort”. If the sweet wort is concentrated to a syrup or even dehydrated to a power this is called extract.
There are many companies that make extract for use in beer making. The beauty of using extract is that the hard work is done – just add the extract to water and you have sweet wort and you can make beer.
Liquid Malt Extract (LME) is the syrup form and has a shorter shelf life, but is a bit cheaper. Dry Malt Extract (DME) is the powered form and has a longer shelf life, but generally costs more.
Typically LME has a gravity of 1.036 and DME has a gravity of 1.044, and since the mash and conversion work is all done, efficiency is 100%.
Extract comes in different colours and can be different barley types, or even wheat, rye, or other grain types. The big drawback is that the brewer doesn’t have control over the process and is at the whim of the maltster and resulting extract. That being said, great beer can be made from extract if care is taken in fermentation and fresh extract is used.