Plants are very special living organisms here on Earth because they do not have to take up food to get energy for grow. Their chloroplasts can use the energy from sunlight to make sugar in a process called photosynthesis.

Now, even though plants normally use light to produce food via photosynthesis, most plants can be induced to live in the dark if given a source of carbon (such as sucrose, a sugar) in their water. However, the plants probably won't develop normally if kept totally in the dark and they will eventually die.

So, to answer your question: Yes, beer might be a source of sugar for some time - but I am not sure if the alcohol is healthy for the plant - and sugar water would definitely be a better source, but I know for sure that a plant will not grow faster in the dark but rather not grow at all.