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The definition of light beer is that it has less calories then it's premium counterpart. It can be one less calorie and legally be called "light."
Depending on the brewer they lighten the beer by using adjuncts like rice or corn which will add fermentables but nothing else to the beer. If you took two recipes and formulated one all malt to a starting specific gravity of 1.040 and the other as a 60% malt and 40% adjunct to a starting gavity of 1.040 and then fermented them both down to 1.004 you would have a beer with identical alcohol content but the one brewed using adjuncts will be lighter in color, body, flavor and calories.
A trick they use to lighten the body, flavor and calories is to add enzymes (alpha or beta amylase) to the mash tun. These enzymes will work on the 1-4 and 1-6 bonds to reduce starches in to simple sugars. The specific enzyme you might find them using is amyloglucosidase. These sugar are what the yeast will use to create carbon dioxide and alcohol.
Now well modified malt will have these enzymes present and you can control which ones are more active by changing the mash temp. A low temp of say 148F will favor Beta amylase and you will have a mash that is more fermentable then one at 158 in which alpha amylase is working and produces more dextrins which are not fermentable. These dextrins would lead to a heavier body, more carbs and higher calories.
Now the mash with the high proportion of adjuncts will be unable to convert itself even though it has some malt in it. The amount of enzymes from the malt is not enough to convert all the mash so they will shoot for a low mash temp and the add the appropriate enzyme to make a mash that is almost 100% fermentable. Since all the sugars will be turned in to alcohol during fermentation this will leave a beer with a thin body, light color and less calories/carbs.
One way they can get by with adding less enzymes is to use a 6row barley instead of a 2row. 6 row is a smaller kernel with less starch material but they generally have a higher kolbach/lintner index which is the ability of the enzymes present in the malt to convert the starches in the malt in to sugars. 6row is the grain of choice for AB, Coors, SABMiller since they have a high proportion of adjuncts which cannot convert themselves.
Anyway, in a nutshell that is how they get lighter beers.
Light beer is a waste of time. Head to your local pub and grab an IPA.
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An Army of sheep led by a lion can easily defeat an army of lions led by a sheep.
Last edited by brewmonkey; 02-15-2005 at 11:23.
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