The soy carbohydrates in tempeh become more digestible as a result of the fermentation process. In particular, the oligosaccharides associated with gas and indigestion are greatly reduced by the Rhizopus culture. In traditional tempeh-making shops, the starter culture often contains beneficial bacteria that produce vitamins such as B12 (though it is uncertain whether this B12 is always present and bioavailable). In western countries, it is more common to use a pure culture containing only Rhizopus oligosporus, which makes very little B12 and could be missing Citrobacter freundii and Klebsiella pneumoniae, which have been shown to produce significant levels of B12 analogs in tempeh when present. Whether these analogs are true, bioavailable B12, has not been thoroughly studied yet. The fermentation process also reduces the phytic acid in soy, which in turn allows the body to absorb the minerals that soy provides.