Ok, so it isn't exactly a plant or an animal, but it will produce an indoor crop that is usable,giftable, or salable.

Kefir is made two ways: with a culture, or with grains. It is a milk or water based drink that is loaded with probiotics, and can be made into dips or cheese as well as used for healthy mixed drinks.

Culture wears out after several times, because it gets contaminated by other opportunistic bacteria which are stronger than the remaining cultures.

Grains have a gelatin like matrix that the cultures live within, and create as they multiply. We can assume it originally generated in an environment with conditions particular to yak milk, horse or yak hide, and the naturally occurring bacteria and fungus indigenous to the Steppes of Mongolia. The nomadic people would put milk into skin bags to store, where it would culture like buttermilk. New milk was likely added on top of old, giving the yeast and bacteria ample opportunity to form a solid matrix at the bottom of the bag. Kefir grains were then divided and passed on, and cultured in other containers. They were kept within the nomadic peoples, and not allowed out of the country for centuries. Eventually someone smuggled some into Russia, where it made its way around the world.

Kefir has the advantage of culturing at room temperature. The grains will multiply over time, doubling in approximately 1-3 weeks. They have become a symbol of sharing in the natural health community, though many people sell them as well. Prices range between $10 and $20 on average, for anywhere between 1 and 4 tablespoons of grains.

Kefir grains are now available for milk or water. They have similar health benefits, but not identical, because they each grow slightly different complements of bacteria and fungus strains. Water kefir grows in a mix of water and sugar, and requires occasional boosts of minerals and calcium, which can be provided by molasses and crushed calcium tablets. These minerals are provided naturally in milk kefir.

Milk kefir produces a yogurt style drink, which can be drained to make a soft cheese. Kefir may also be used as a cheese starter, replacing cultures that are commonly used instead.

Water kefir produces a bubbly soda type drink, which is sour like seltzer water. The more sugar you add, the sourer it gets, because the bacteria and fungus converts the sugar – the more sugar, the more they convert, and the sugar is converted to the sour flavored elements. The same thing happens with milk kefir, but it is lactose that is converted instead, leaving kefir a largely lactose free product.

Water kefir can be made into soda style drinks by sweetening lightly and adding flavoring such as lemon juice, vanilla, rootbeer flavoring, lime and ginger, orange juice or tropical punch, or other flavorings. There are many instructions online for making soda type drinks involving addition of fruit or juice, and a second fermentation. Don't do this unless you want hooch. This WILL produce a drink with significant alcoholic content.

Daily care involves straining the grains from the finished kefir, and putting them into new milk or sugar water. If water kefir starts to look funky or the water smells funny, it usually is in need of calcium or minerals.

When you get new grains, they sometimes need to “condition”, until the balance of bacteria and yeast is right. You may need to do this after freezing or refrigerating grains also, because the cold knocks them out of balance. Conditioning is done by straining and replacing the milk or sugar water daily, until it “smells like food”. Can take up to a week.

You can store grains by freezing, or refrigerating. They may be frozen for up to 6 months. If refrigerated, they should be stored in milk, and the milk should be replaced every 2-3 weeks. Don't store for more than a round or two in the fridge – different fungus and bacteria flourish at 40 degrees than those that like growing at room temp.

Grains may also be dried, and stored for up to 6 months.

The grains are edible, much like tapioca, but most people prefer to share them rather than eat them.

Milk kefir may be double fermented. After the finished kefir is strained, it can be combined with additional milk and left at room temperature for another 24-48 hours. You can quadruple the volume, or more, by this process, which helps you get a lot of kefir quickly if you need it. The balance in this may be slightly different, but is close enough to not be a major issue. This is a good way to get enough for making cheese.

Milk kefir prefers raw milk, but can use most kinds of milk. Some people say not to use Ultra Pasteurized (because the proteins have altered, and the carbs and fats are bound in ways that are unnatural), but frankly it is very hard to tell whether milk is ultra pasteurized now or not – it is not always labeled that way. Whole milk is best if you use commercially processed milk.

Water kefir REQUIRES non-chlorinated water. Either use bottled water, or boil the water for 10 minutes and then let it sit overnight to cool and evaporate a little more before using it with your kefir. We boil water and store it in glass jars for later use.

Kefir requires daily care, and a good supply of milk or sugar water, but it keeps on going. It is the simplest cultured milk to maintain, because it cultures at room temperature instead of requiring heat for incubation. You also do not need to re-pasteurize the milk prior to adding the grains, because the cultures are strong enough to overpower pretty much any opportunistic contaminants. You do have to watch the amount of grains though, so you either add more milk or separate some of the grains off as they expand.

There is a significant alcohol issue with water kefir. Many sources recommend a second ferment to create other drinks – they will advise putting in fruits and other ingredients, and then re-fermenting, to make soda or other drinks. If you do that, you get wine. Don't do that, especially if you are giving it to children. Remember, if it smells or tastes alcoholic, it IS.

All fermented foods contain minute amounts of alcohol, which diminish when the fermentation is done correctly, and is never enough to intoxicate or come even close to being “strong drink”, or “wine”. Even vinegar has a small amount of naturally occuring alcohol, but it is so small that it is safe to use (and not a violation of the LDS Word of Wisdom, which specifies “wine, and strong drink”). Properly used and maintained water kefir falls into the same category as vinegar, sauer kraut, brined pickles, and other healthy fermented foods.

There are various sites online that delve into the alcohol content of water kefir soda, and various fermented concoctions from kefir, but they do not distinguish between kefir WITH fruit, and that without, which is a huge issue, and the one site we found where someone tested it, they heated the soda prior to testing, which invalidates the results since alcohol evaporates rapidly in heat. Most people who make water kefir drinks never bother to use their nose to test, and they do not pay attention to what does and does not produce an alcoholic effect.

If your sugar water kefir smells like alcohol, the balance is off somewhere. A loose lid, or cloth covering instead of tight lid will help, as will making sure that it has the proper mineral feeding. A tiny pinch of sea salt for a 1 pint batch can also stop the alcoholic smell if you can't get it to go away (careful not to overdo the salt, it can inhibit some bacterial or fungal growth).

As long as you do a proper single ferment with water kefir, and flavor with fresh flavorings, and do NOT re-ferment, it will not contain any significant amount of alcohol, and you won't accidentally intoxicate your kids or the neighbors.