Create the starter not only to increase the yeast, but also to increase lactic acid for safe fermentation.
The percentage of koji in shubo is around 30-33%, and the total percentage of the koji is 20-23%.
If the whole amount of rice is 1000kg, approx. 200kg is the total amout of koji. In shubo, 60kg is koji.

For temperature control of shubo, an equipment called daki, stainless steel made bucket-like tool used with hot water or ice, is used.
Alternatively pipes, jackets of hot or cold water are also used.

For acidity, brewers try to increase the amount of lactic acid.
One method is directry adding lactic acid(sokujo), another is to mix the rice very well to grow the population of lactic acid.

The temperature is 20-25c, takes 14 days to grow.
Less umami and acidity in the taste.

Kimoto and Yamahai
The temperature is around 6-7c, takes about 28 days.
First bacteria converts nitrates to nitrites, then lactic acid are created.
High concerntration of sugar, low PH, low temperture avoid the growth of undesireble yeast.
Yamahai was born in 1909, by skipping the stage of turning rice into paste.
More umami and acidity, can be more interesting flavour. 

Other kinds of  shubo
・ko-on toka moto
・Improve techniques (Higer temperature sokujo-moto, kimoto mixing machine)
・No shubo used (when black or white koji is used citric acid is enough to kill the undesireble yeasts)