Endemic plums is purely wild plums with 10000 or longer history in Korea peninsula. They are very strong botanically and the principal element, citric acid is more superior than contained in improved breeds of plums. The time plums become ripe enough is generally near the middle or last days of June. Even though plums are ripe, it is easy to break tooth if taking as raw plums. In addition ripe plums cannot be stored for long time despite refrigerating or freezing processes like bananas.
Thus our ancestors have used plums as a kind of medical elements by salting to make Baekmae and smoking to make Omae (From Dongeuibogam).
Nowadays scientific ways to process ripe plums and preserve citric acids are developed well. This introduces how to process plums to make alcoholic drinks, Jangajji (dried and/or seasoned foods), and undiluted solution of plums.
Soju Solution
Prepare 10kg of plums and 10 bottles of 1.8L Soju (25Do). Soak plums in Soju in a
Korean jar and cover with Korean traditional window?paper. Store it in the shade.
After 3 months (near Chubun ? September 22), filter the soaked drinks. For 1L of
filtered drink, dilute with 2~3L of 25Do Soju.
According to the tastes, add brown sugar. Store drinks in a glass bottle under
the shade. The longer the drink matures, the better the drinks tastes.
Clear brown colored drink has a very nice scent and taste.
Sugar solution
Mix 10kg of plums and 5kg of brown sugars in a Korean jar. Cover with brown
sugar. With a plate, cover the jar and seal the jar with the vinyl.
Brew for 3~4 weeks in the shade. On a clear day between Chobok (July 17) and
Jungbok (July 27), filter the brewed drinks.
For 1L of filtered drink, dilute with 2~2.5L. Store in the same way with the Soju
solution.
Mix 10kg of plums with 1~1.5kg of sun?dried salt and put it in a Korean jar.
Cover the mixture with salts. Close the jar with inner lid put some stones to press.
Seal the jar with the vinyl.
After ripening for 3~4 weeks in the shade, plums would shrink and clear and brown
water would be generated. If using a glass jar, the ripening process would be seen.
The water is Baekmaecho and shrunk plums are Baekjangajji.

Baekmaecho is very good for health and it can be used as a salty condiment.
To make Hongmaecho/Hongjangajji, Chajogi (a.k.a. Chamsoyeop ? purple perilla plant) should be added to Baekmaecho/Baekjangajji. 3kg of Chamsoyeop leaves is needed for 10kg of plums.

Soak Chamsoyeop in 1/10 salty water for 1~2 hours. Soaked water is needless.
Scrub salted Chamsoyeop leaves with salts for 10~20 minutes. Blackish brown
water is generated and the leaves become fibrous.
Pour blackish brown water into the Baekjangajji jar and cover with fibrous leaves.
The water and plums will be purple color by the litmus effect.
Leave the jar sealed for 3 days~3 weeks since it is the rainy season.
After the season is over, dry the plums for 8~10 hours under the sun.
Take care of plums not to stick together.
Put the dried plums into the jar again.
Select some fine day and repeat the process of 5 and 6 for 3~4 times in order to
make the plums absorb the color.
On the last day, leave the plums for a clear night. In the early morning, put the wet
plums with morning dew into the jar. Seal and store the jar under the shade for
ripening until the middle of October. The plums would be the best Honghangajji
(Umeboshi in Japan)

Notes for making Honghangajji
Plums should be ripe enough and one side of the fruit should be brown color.
Sizes of the plums should be regular without any scratches.
The jar should be glass or ceramic jar.
If plums catch in a sudden shower, disinfect the plums with Soju. Scratched plums
are like Honghangajji.
1. Steam the plums and dry under the sun. Store it at the room temperature.
1. Boil down 1 or 2 plums a day. Upon the taste, add sugar or honey.