Zip thousand files in php - memory leak - php

Question

I have to zip search results containing maximum 10000 files, with an approximate dimension of far more than 1Gb.
I create a zip archive and read every file in a for loop whit fread and add the resulting file to the archive.
I never finished adding files because of this error
PHP Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 1257723 bytes)
but I don't think adding 1Gb or more to the memory_limit value of php.ini could be a solution, because memory resources are limited.
Because of the zip file will stay in memory until it will be closed (or so I read in another question), I made a way to create a series of zip file of 50Mb to avoid the memory leak. But even if the php script create another file zip, it will stop with the same PHP Fatal error on the same file (the 174th).
Why?
Am I doing something wrong?
Any help will be appreciated.
Here is a code snippet of the file creation
$zip = new ZipArchive();
$nomeZipFile = "../tmp/" . $title . ".zip";
for ($x = 0; $x < count($risultato); $x++) {
$numFiles = 0;
$dir = '../tmp';
if (file_exists($nomeZipFile)) {
if (filesize($nomeZipFile) > 52428800) {
// filename count
if ($handle = opendir($dir)) {
while (($file = readdir($handle)) !== false) {
if (!in_array($file, array('.', '..')) && !is_dir($dir . $file))
$numFiles++;
}
}
$nomeZipFile = '../tmp/' . $title . $numFiles . '.zip';
$res = $zip->open($nomeZipFile, ZIPARCHIVE::CREATE);
} else {
$res = $zip->open($nomeZipFile, ZIPARCHIVE::CREATE);
}
} else {
$res = $zip->open($nomeZipFile, ZIPARCHIVE::CREATE);
}
...
// adding file
$fileDownload = "";
$fDownload = fopen($kt_response->message, "r"); // the file is downloaded though a webservice
while(!feof($fDownload)) { $fileDownload .= fread($fDownload, 1024); flush(); }
$zip->addFromString(filename, $fileDownload);
....
$zip->close();
}