How about a little refactoring to better understand your code?
var table_size = $('#table-body tr').length;
var trs = $('#recipiestable tbody tr').slice(table_size);
$.each(trs, function(i, tr) {
// No need for messy lookups, if you can look inside the context of your current tr
var ingredients = $('td:nth-child(1)', tr).text(),
amount = $('td:nth-child(2)', tr).text(),
unit = $('td:nth-child(3)', tr).text();
$('#resultsbody').append('<tr><td>' + ingredients + '</td><td>' + amount + '</td><td>' + unit + '</td> </tr>');
});
docs for $.each