the $\bar{B}B$ pair will always have two quark flavours in common, in conflict with experimental data from $e^+e^-$ annihilation. A modified model with a stepwise production mechanism (called the popcorn model) was presented in [@Andersson:1984af], and has since been incorporated in [P]{}.[^5] In a red–antired ($r\bar{r}$) string-field a $g\bar{g}$ quark pair can be produced as a vacuum fluctuation (see [figures [\[fig:popcorn\]]{}]{}a and [\[fig:popcorn\]]{}b). If the $r$ and $g$ charges form a $\bar{b}$ antitriplet, a $\bar{b}b$ field can be formed between the new quarks, which means that the net force on the green quark or antiquark is zero. During this fluctuation a $b\bar{b}$ pair produced in the string can split the system by an effective diquark–anti-diquark production (see [figure [\[fig:popcorn\]]{}]{}c). In this way one (or more) mesons can be produced between the baryon and antibaryon.

As hadronization is a non-perturbative process, estimating all possible hadron species in an MC implementation necessarily implies a set of additional phenomenological parameters, which all have to be tuned to experimental data. Although [P]{}has adopted the popcorn model, it is reformulated in terms of diquark breakups with an additional probability for having mesons produced in between baryon pairs as in [figure [\[fig:popcorn\]]{}]{}d. Most important for the 