"I never heard of a Umeboshi plum. How are they different from a regular plum?"
Umeboshi [oo-meh-BOH-she] is actually not a plum. It is very close relative to apricot. It is an Asian apricot (Prunus mume), and it has uniq healing abilities. It is tonic for stomach, liver, gallbladder, intestines.
It has ability to balance foods that we are unable to tolerate.
As almost every gallbladder attack is caused by the presence of foods in our GI tract, foods that we are unable to tolerate, Umeboshi is a perfect anti-pain meds.
Main ingredients of UMEBOSHI are "apricot (UME)", Sea Salt (BO), and shiso (SHI) leaves.
Shiso (beefsteak plant) (Perilla frutescens (L.) Britton) is a mineral-rich herb that is pickled with umeboshi. In addition to food coloring , perilla (shiso) adds a antimicrobial agent to pickled foods.
Asian herbalists prescribe perilla for cough and lung afflictions, influenza prevention, restless fetus, seafood poisoning, incorrect energy balance, etc (summarized by Brenner 1995). Studies of perilla volatile oil have revealed that distinct chemotypes of perilla have dramatically different biological effects (summarized by Brenner 1995). The perilla aldehyde chemotype is the source of Japanese "ao-shiso" a medicine with an agreeable fragrance.
Prunus mume (UME), better known as the Plum or Japanese Apricot tree, was brought to Japan from China in the eighth century. Although there is only one species of ume, there are over 300 varieties, varying in color, shape and size, but all have fruits that are smaller and less sweet than their European contemporaries. The unripe fruit are used to make wine, vinegar or are pickled.
Umeboshi are made in June, when green, immature plums come onto the market. They are cured in salt for about two weeks, then packed with salted shiso leaves (beefsteak plant) to impart a red color and marinated for a further four weeks. They can either be eaten straight from the jar or sun-dried for a few days, until they resemble an anemic prune.
In the Edo Period (1600-1868) it was realized that eating umeboshi could combat fatigue. The citric acid in the fruit converts lactic acid into water and carbon dioxide, which can easily be discharged from the body. If allowed to accumulate in the body, (usually as a result of an inefficient flow in the Kreb's Cycle,) lactic acid can cause tiredness and exhaustion. Obviously samurai didn't understand the scientific reasoning behind this, but they did realize that if they always had a ready supply of umeboshi they could be alert and ready for action.
The demand for umeboshi also steadily increased due to its use as a color fixative for cosmetics, a fabric dye and a medicine.
The first record of umeboshi being used for medicinal purposes is in the tenth century, when it was reportedly used to treat Emperor Murakami. Throughout history, this sour fruit has been used as a cure for vomiting, intestinal worms, fevers, coughs and colds. Today the older generation still say "One umeboshi for breakfast will save you from diarrhea!" and many Japanese regularly eat one every morning, washed down with copious cups of green tea.
In fact there is quite a lot of scientific evidence to support the benefits of eating umeboshi. The sour, alkaline taste stimulates the secretion of saliva and gastric juices, activating the digestive system. The citric acid in the dried fruit also increases metabolism and, more importantly, assists the absorption of calcium in the intestine. The pyric acid in ume fruit enhances liver function and can help break down alcohol in the liver, so it is often recommended to eat umeboshi (and drink a large quantity of tea) as a hangover cure.
An old-fashioned herbal pain-killer is bainiku-ekisu, (literally "ume flesh extract") although it is actually grated, condensed flesh rather than an extract. Bainiku-ekisu can be applied in a poultice to the cheek or forehead as a cure for tooth and headaches. Another old wives remedy for coughs and colds is umeninnikunegi (pickled ume, garlic and leek soup). The theory behind this soup is that both umeboshi and garlic have sterilizing qualities and leek alleviates fevers.
A more popular way of eating umeboshi is as a dressing, known as umeshoyu; one finely chopped umeboshi is mixed with two tablespoons of shoyu (soy sauce) and sake (rice wine) or mirin (sweetened sake) to taste and served with chicken, seafood or salad.
In addition, this wizened little fruit also acts as a sterilizer and antibacterial agent. It contains organic acids that can kill bacteria, so an umeboshi is usually included in a bento lunchbox, as a "garnish," to prevent food-poisoning, especially during the summer months when bacterial growth is greatest and hydrochloric acid levels in the stomach are lowest. It is also added to onigiri riceball-fillings to prevent spoilage. Truly a fruit for all seasons!
Whether consumed as a sweet, fruit, paste, dressing or medicine, there seems little doubt that eating an umeboshi a day may keep the doctor away.