Slaves would usually have been familiar with alcohol, even if they did not get it that often. The general rule on plantations most of the time was that alcohol was forbidden to slaves. This was not solely based on race, as many southern elites worried about the effects of alcohol on white men as well. There are several instances where this rule was bent or broken, in fact, and on some plantations alcohol was a common feature. It seems to have been a case by case basis.

The one you mention in your question might be the most common. Alcohol played an important cultural role on special occasions. Sometimes the alcohol was supplied by the master himself in a paternalistic gift to his slaves. When slaves got married to each other, for instance, there are a number of examples of the master supplying food and drink for the festivities and even attending the party, so to speak.

Holidays, especially Christmas, were another occasion where the master might well provide the slaves with alcoholic beverages. In one case i have read about the ritual of making eggnog was an important aspect of the holiday, but in many cases drink flowed liberally for the enslaved and the slave owners alike. In the eggnog case, the master made a whole ritual out of it, handing one glass to each of his slaves personally. Frederick Douglas made note of the tradition of master giving slaves strong drink himself, arguing that the slave owners not only allowed their slaves to drink, but encouraged them to get smashed. This was a way for the slave owner to provide "proof" that the slaves did not deserve freedom. A kind of "Look at what they do if we let them off the leash" mentality, if you see what I mean.

At other times, the slave owners or overseers might pass out liquor even during regular days to lubricate the means of production. Even as they were working in the fields, occasionally a "little brown jug" was "passed 'round" to warm the slaves and give them more energy. Sometimes a sip of hard liquor was a reward for working hard as well.

There were many instances of slaves obtaining alcohol outside of the specially sanctioned occasions that their masters allowed. On some plantations brewing cider, beer, and/or brandy was part of the duties of the female house slaves. So, the slaves were very familiar with the brewing process, but also with where the alcohol was stored. Theft for parties was very common and alcohol was a large part of that. Female slaves would either directly steal the alcohol or "forget" to lock it up so some other slave could steal it. They would then drink the alcohol at their own secret parties, often away in the woods or in abandoned buildings. Frequently they drank to excess, but this too was a form of resistance in its own way as hung over slaves were not likely to work very hard.

Black market liquor was also relatively common. There was a whole underground economy surrounding slavery that was not on any official record. Alcohol was an important part of that and slaves could fairly easily have bought some if they desired to do so. There were even some bars and public houses that served slaves.

All that being said, most slaves would have been familiar with alcohol in general. But, as you may have noticed from my examples above, they would have been most familiar with strong liquor, especially whiskey, as that was the most common way to consume alcohol at the time. By the 1830s Americans over the age of 15 drank more than seven gallons of alcohol a year. It is possible that Django had never tasted beer, even if he was familiar with other forms of alcohol.

Further reading: Stephanie Camp, Degrees of Freedom, Stephen Nissenbaum, The Battle for Christmas, Seth Rockman, Scraping By, Jeff Forret, Race Relations at the Margin.