With milk kefir becoming such a popular drink, you're probably wondering if there are any drawbacks. Based on my research (which is continual as new science emerges), I've come to the conclusion that properly fermented milk kefir is even more safe than raw milk. The milk kefir grains contain powerful bacteria and yeasts that can fight against harmful bacteria such as E. coli. That being said, you can experience negative events from kefir. The most common negative experience is diarrhea or constipation. These negative symptoms can occur when you drink too much kefir at once, especially when you are new to kefir. With strong probiotic foods, it is best to start small. Depending on how sensitive you typically are to new foods, you might choose to start with only a tablespoon to a quarter cup, and increase the amount every 3 or so days. This can help you avoid a negative experience from milk kefir. Otherwise, I would not worry about consuming milk kefir if it is fermented properly. It should have a somewhat pleasantly sour smell, and the taste will vary based on the type of milk used and how long it has been fermented. It can range from mildly tart to quite pungent. Your kefir should not have any off colors or fuzz such as yellow (beyond the natural color of your cream), pink, green, or grey. It should not look, smell or taste moldy. Do not consume if you witness any of these things. If you are particularly concerned, you can invest in a pH meter to test the acidity of your finished kefir. The safe zone is below 4.2 pH, and my kefir generally tests at around 3.7.