yogurt is around rm5 / 500ml ( 1 tub ), fresh milk is around rm6 / 1000ml, cheapest solution is... but 1 tub yogurt and 1 liter fresh milk... 250ml yogurt mix into 500ml fresh milk ... in 8 hours it will turn into 750ml yogurt ( which keeps for almost 2 weeks )... yogurt such as n*stl* has 4 types of lactobacillus in it... so... by adding 250ml yogurt to 500ml milk.. you are 'multiplying' these bacteria which in turn will be put into your tummy when u consume them... do the maths... its actually very very economical... i hav been doing this for years... but i ferment raw milk... not fresh milk... uht milk cannot be turned into yogurt... lactobacillus cant survive will in uht milk... ultra heat treatment 'burns off' too much nutrients... if you are really keen on fermenting yogurt... i am willing to share... just pm me..

if i ferment my yogurt for more than 24 hours, will there still be lactose?

ferment your own kefir, 20+ strains of lacto bacilli and several strain of yeasts, http://www.healingcrow.com/ferfun/conspiracy/conspiracy.html , cost? buy raw / pasteurized milk, ferment 8-12 hours, that is all