Each value is a single value. However that single value is allowed to be a reference.

Try something like:

while (not $done)
{
  my $name = 'Placebex';
  my %info;
  $info{concentration} = 0;
  $info{volume} = 250;

  $recipe{name} = \%info;
}

foreach my $name (keys %recipe)
{
  print "Take $recipe{$name}{volume} ml of $name,\n";
}
print "and call me in the morning.\n"
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