The question seems to be asking for the ingredients allowed under the original rules. Those only allowed barley and no other malts. Yeast shouldn't be allowed because it was not one of the permitted ingredients under the 'pure' beer rules. I don't think it had even been discovered when the rules were written.
No yeast, no beer... The current german "purity law" allows yeast (obviously). There are no "original" rules, just many different rules in different times and different regions of today's Germany. The older ones don't mention yeast, as until about the 16th century people didn't know its essential role for brewing beer (some of the rules even don't mention water!). People then only recognized that bakeries were most successful in brewing. But they thought it to be a miracle by the gods... Today everyone knows yeast to be indispensable and to notably define the taste of beer. I definitely would add yeast to the list, because: no yeast, no beer ;-)
I think the question refers to the purity law of 1516, which is commonly considered the original or definitive one. Under that law, only hops, barley malt and water were allowed. Yeast was not mentioned because people back then didn't know about yeast, they used spontaneous fermentation. But of course, yeast is allowed nowadays.
I typed the German versions for everything here except for bordering countries and I'm glad they were all accepted. The choice of questions was good too.
I thought there would be more people with the last name "Meier" than "Fischer". Probably because there's also the similar "Maier", "Meyer" and "Mayer".
Because the flowers of the plant are referred to in the plural, and it is the flowers that are an ingredient of beer. The plant is referred to in the singular.
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