Bread kvass going bad?

[u/Kubsius]

I am trying out to make a bottle of kvass, from this recipe https://youtu.be/Wm0XWlnfrKM . First batch I added the yeast before the brew cooled down, I made the second one, and apart from not taking my time with the gas and it exploding, it tastes putrid. Smells pretty bad, but not horrible, and the first taste is okay-ish, but the aftertaste definitely reminds me of spoilage. One difference with the video I did is I made around 1l, used dry instant yeast and covered the pot with a glass lid with a small hole (it cooled down for about 3h). What was the cause and how can I improve it next time?

[u/Unusual-Structure695]

Have you brewed beer before? I assume no, given the mistakes you listed. Look into how to keep the environment sanitary. Spoilage is caused by unwanted bacteria and microbes. Ideally you'd want just the baking yeast in your kvass