Make your own kefir. By fermenting the milk, you obtain a delicious drink, very nutritious, and easy to digest. In the process, even commercial milk will get back some of the lost enzymes through pasteurization.
You will get two tablespoons of fresh kefir grains, so you can start making kefir, and growing your own mushroom.
The grains have never been dried or stored in the fridge or freezer, which makes them more active, and healthy.
The kefir grains come with a two pages instruction booklet, which for many begginers can be not enough to start. Occasionally, the grains arrive dead at the destination because of handling and transportation. In 90% of cases though, they arrive in perfect conditions.
Make sure you discard the first few batches, they will be either too sour, or funny tasting. This happens because some of the cultures in the kefir need more time to recover, so the fermentation will be done by only some of the cultures, and not all of them. When all cultures are back in shape you should be getting the nice smooth, kefir taste.
You need to use pasteurized milk and not ultra pasteurized. To know which milk is good, just leave overnight a few spoons of milk in a cup. If it turns sour, is good, if it doesn't, it is not. You might need to let the milk for two days, depending on the ambient temperature.