In a previous article in which I discussed the original source of the Reinheitsgebot, or purity law, I argued that the mention of barley instead of malt is of significance. Any use of unmalted grains is of course rejected by proponents of the purity law, and also the modern beer legislation, the Vorläufiges Biergesetz, codifies malted barley as the only allowed grain for bottom-fermented beer, and malt from any grains for top-fermented beer. In Germany, it is at the moment not allowed to brew beer that contains unmalted grains, adjuncts, or “Rohfrucht” as they’re called in German.
Already back in the 1960’s, the Reinheitsgebot proponents were fiercely against any change in German beer legislation and any attempts in harmonizing German legislation with EC legislation. The great fear was “chemistry” and “chemicals”. First there was the fear of hop extract, then there was the general fear of chemicals, culminating with the infamous Franz Josef Strauß warning about “chemistry in the beer”.
Even today, reinheitsgebot.de insists that the use of unmalted grains requires artificial enzymes (see answer to question 2) to convert its starches into fermentable sugars. Nothing is further from the truth. To explain why, I need to talk about why barley is malted in the first place.
The process is malting means that barley kernels are soaked in water. This starts the germination process, the barley basically starts the growth process. This produces enzymes that can convert starch into simple sugars, cell walls in the grain and proteins start to break down, the whole grain is being modified. If the maltster lets this process continue, whole plants would start to grow, and nothing would be left of the grain. That’s why after a few days, the so-called green malt is dried and kilned. Kilning at lower temperatures gets you a paler malt in colour, while kilning at higher temperatures gets you darker malts. The kilning process also destroys some of the enzymes. But brewers need these enzymes to later convert the malt’s starches into simple sugars during mashing. So it is the maltster’s job to produce malt that still contains enough enzymes.
The amount of enzymes in a certain amount of malt decides what amount of starches can actually be converted. This is called diastatic power. Paler malts usually have a higher diastatic power, while darker malts often have a lower diastatic power. Dark malt, like dark Munich malt (used to make dark-brown lagers, the classic Munich style of beer), has just enough diastatic power to convert itself, but not more. A lot of specialty malts, like caramel malts, dark kilned malts, and roasted malts have no diastatic power at all. They always require a certain share of enzymatic base malts to convert their starches.
Diastatic power for malts is specified in either Windisch-Kolbach units (°WK) or degree Lintner (°L). Conversion between the two is easy: °WK = (°L * 3.5) – 16. Usually, about 105-125 °WK (~ 35-40 °L) are necessary in a grist to fully convert all starches. Base malts can range from 140 °L (Pilsner malt) down to 40 °L (Munich malt) in diastatic power. A chart with typical values can for example be found here.
So, in order to brew with unmalted grains, there are two things that you need to make sure: first, you need enough enzymes by adding enzymatic malt into your grist, and second, you need to make sure that the enzymes can reach the starches. Some adjuncts thus need to be cooked or otherwise treated with heat to make the starch accessible. Flaked barley can be boiled, corn can be made into flakes (like cornflakes, except your breakfast cereal is fortified with a whole lot of other things that you may not want in your mash), oats can simply be rolled, while wheat can be torrified.
Calculating how much malt you need is easily. Suppose you have a base malt with 110 °L diastatic power. In total, you need 40 °L in your grist. That means you need at least 100*40/110 = 36.36 % of base malt in your grist, the rest can be unmalted grains. The lower your diastatic power, the higher your share of base malt, and with 40 °L Munich malt, you need 100*40/40 = 100% base malt.
So why is an all-malt grist still promoted? Because of historic reasons. Brewers back in the day could have easily worked with unmalted grains, and probably also did. But back then, even the malt wasn’t quite the sure thing as it is now: maltsters several hundred years ago didn’t have the ability to finely control, measure and evaluate their malt production. Historically, malts were often relatively dark (because it’s hard to finely control kilning temperatures), undermodified (i.e. some of inner structures weren’t properly broken down), and low in enzymes. These types of malt are hard to work with, unless you employ certain techniques. Decoction mashing, as practiced by German brewers for centuries, is one way of making the most out of malts that were badly modified and low in enzymes. In the 19th century, one of the big achievements of continental brewing was to learn how to produce pale kilned malts, but the decoction mashing tradition remained.
British brewers on the other hand, who had known how to produce pale malts for much longer, have traditionally employed a mashing regime which is nowadays often called a single-step infusion mash. The grist is infused in water and rested at a certain temperature. Because the malt is better modified, and relatively rich in enzymes, it can easily convert all the starches without requiring decoctions to make it more accessible. The same technique is employed by most homebrewers nowadays due to the high quality of malt, as well as commercial brewers that try to avoid energy-intense decoction mashes. Adjunct brewing is a well-researched topic in brewing science, and even German scientific brewing literature contains plenty about it.
So, from a purely technological point of view, there is no argument against the use of unmalted grains when producing wort. With some care, adjuncts can be easily used without requiring any artificial enzymes or other “chemistry”. Brewers can also benefit from a wider range of base materials, as unmalted grains often impart slightly different qualities in the beer compared to their malted equivalents. It is not bad per se, nor is it artificial. Rejecting unmalted grains is dogmatism, in my opinion, as it provides and ensures no quality in the beer, but instead just arbitrarily restricts brewing and thus variety.
In the end, the prohibition of unmalted grains in German beer is also an insult to German malting. German maltsters produce a wide range of all kinds of base malts and speciality malts, exactly matching very strict specifications in colour, kernel modification, friability, protein content, diastatic power, and a whole lot of other properties. At the same time, German legislation specifically disallows German brewers to build upon some aspects of this high quality work. And the proponents of the Reinheitsgebot even support that, even though it makes no sense other than to bring up that bogeyman that is “chemistry in the beer”.