Since that is romanized, it gives me a chance to explain something. You will see it romanized differently, and spelled slightly differently. I first started learning to read and write Korean in 1984, and when I was taught, there was a very rigid system that was used for transliteration. Some people still use this, but sometimes, it really doesn't make sense phonetically. Sometimes, none of the systems that are used really make sense phonetically. (An example is the Korean surname: Choi. Whenever an English speaker sees that, they want to pronounce it like "Choy," but the Korean dipthong that is transliterated "oi" actually makes a sound similar to a short "e." So that baseball player Hee Sop Choi ... that last name should sound more like "cheh.")
Hangul is the Korean alphabet, and it is an alphabet - different from the Japanese syllabary or the Chinese character based system (which is also used in other countries in one form or another). So in Hangul, it is written:
Each character grouping is one syllable. You can see the Hangul on the bottle, but it is a calligraphy style, so if you're not accustomed to seeing it, it may be difficult. The spellings come about from this if you follow the groupings:
ㅁ is equivalent to the English 'M'
ㅏ sounds like "ah" in English (There are more vowels in Korean than in English, and unlike English, a vowel in Korean has only one sound.)
ㄱ you see this at the end of the first syllable (on the bottom), and again at the beginning of the second syllable (upper left character in that syllable). It makes a sound somewhere between the English G and K. Often, it is romanized as a G at the beginning of a syllable, and as a K at the end of a syllable. In the spelling on your bottle, they just used a double 'K' which would not be incorrect. I don't normally do it that way though, just because the old style of G and K makes a clearer distinction between this letter and another Korean letter that used to be romanized as K' (with an apostrophe) which was used for another Korean letter with a harder 'K' sound.
ㅓ is about halfway between the English sounds ooh and uh. In words like "Seoul" it is romanized as "eo," but other times, it is romanized just as o. Even though it doesn't sound like "eo" I usually romanize it this way because it avoids confusion with another Korean letter which makes a long 'o' sound. At the time I learned it, it was almost always romanized as "eo."
ㄹ is very hard to describe. It is neither an r, nor an l sound, but actually is between those two sounds. It is pretty close to the Spanish 'r' sound. You see this letter as the end of the second syllable (scrunched down at the bottom), and the beginning of the third syllable (stretched up on the left). Doubling consenants in Korean really means you hold that sound longer, so when I romanize, I will always keep the double consonant like in this case, but in some more modern methods of romanizing, it's not always done - thus the spelling on the bottle.
ㅣis maybe between a short i and long e, but I think it is closest to a long 'e' sound in English, but it is almost always romanized as 'i'. I think this was probably done because this vowel often appears at the end of a syllable, and if it was romanized as 'e', English speakers might assume it to be a silent 'e' and try to apply English pronunciation rules.
Some Korean words are well established in their English spelling and always appear the same. The capital city of 서울, (pronounced as suh-ool) is one such word and is always romanized as "Seoul." Other words such as 막걸리 (the drink we're talking about) are not so well established, so there are many ways they are romanized, and it probably depends on the age of the person romanizing it how likely it is to be spelled one way vs. another. So far as this goes, my wife's hometown of "Pusan" is often romanized as "Busan" these days.
To tell you the truth, it's probably easier to learn to read the Korean alphabet than it is to try to explain why things are romanized a certain way