alignment problem with the + sign in chemfig (zero width arrow)

Question

I created two molecules in chemfig and would like to place a + mark vertically aligned in the middle between the two molecules. There is an example of this demonstrated in the manual (see the code), but i'm unable to reproduce it using my own alignment.

How can I achieve the result I wanted (also tikz hacks are welcome, althought I prefer to stay within chemfig)

\documentclass{article}
\usepackage{chemfig}
\begin{document}
%my molecules, the + sign should be alligned in middle just as the manual example
\schemedebug{true}
\schemestart[][west]
\chemname{\chemfig{C(=O)(-[4]H)-[6]C(-H)(-[4]OH)-[6]CHOH}}{\footnotesize{L-glyceraldehyde}}
\arrow{0}[,0]\+
\chemname{\chemfig{COO\textsuperscript{-}-[6]C(=O)-[6]CH}}{\footnotesize{pyruvate}}
\schemestop

\bigskip
%example taken from the chemfig manual (page 67)
% + sign is correctly aligned to the middle.
\schemedebug{true}
\schemestart[][west]
\chemfig{C(<[:40])(<[:160])=[6]C(<[:-130])<[:-20]}
\arrow{0}[,0]\+
\chemfig{\lewis{246,Br}-\lewis{026,Br}}
\schemestop
\end{document}

Answer 1

You could simply insert a second invisible arrow and maybe use the optional arguments of \+{<dim1>,<dim2>,<dim3>} (where <dim1> is a horizontal space before the plus <dim2> a horizontal space after the plus and <dim3> a vertical shift) to adjust the plus vertically

\documentclass{article}
\usepackage{chemfig}
\begin{document}

\schemestart
\chemname{\chemfig{C(=O)(-[4]H)-[6]C(-H)(-[4]HO)-[6]CH_2OH}}{\footnotesize{L-glyceraldehyde}}
\arrow{0}[,0]\+{,,1.5em}\arrow{0}[2,0]
\chemname{\chemfig{COO^{-}-[6]C(=O)-[6]CH_3}}{\footnotesize{pyruvate}}
\schemestop

\end{document}

Answer 2

A better solution is to start the chemfig code of "L-glyceraldehyde" with the middle "H" and to start the one of pyruvate with the middle "C". Then, you don't need the \arrow{0} trick and you don't need to adjust the vertical position of \+

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart
\chemname{\chemfig{H-[4]C(-[6]CH_2OH)(-[4]HO)-[2]C(-[4]H)=O}}{\footnotesize{L-glyceraldehyde}}
\+
\chemname{\chemfig{C(=O)(-[6]CH_3)-[2]COO^{-}}}{\footnotesize pyruvate}
\schemestop
\end{document}