React + Webpack: process.env is EMPTY after run build - node.js

Question

A common problem but as usual, every solution found on this website, not fit my case.
I've create a .env.production file with specific constant.
In my package.json I have:
"build": "NODE_ENV=production webpack --config webpack.config.js --colors",
I run the build with the classic: npm run build
This is my webpack.config
const webpack = require('webpack');
const path = require('path');
var config = {
context: __dirname + '/src',
entry: {
javascript: "./index.js",
},
output: {
// path:path.join(__dirname, './dist'),
path: path.join(__dirname,'../static/js/'),
filename: 'bundle.js',
},
devServer: {
inline: true,
port: 8080
},
resolveLoader: {
modules: [path.join(__dirname, 'node_modules')]
},
module: {
loaders: [
{
test: /\.jsx?$/,
exclude: /node_modules/,
loader: 'babel-loader',
query: {
presets: ['react']
}
},
{
test: /\.css$/,
loader: 'style-loader'
},
{
test: /\.css$/,
loader: 'css-loader',
query: {
modules: true,
localIdentName: '[name]__[local]___[hash:base64:5]'
}
},
{
test: /\.svg$/,
use: [
{
loader: "babel-loader"
},
{
loader: "react-svg-loader",
options: {
jsx: true // true outputs JSX tags
}
}
]
}
]
},
}
module.exports = config;
As you can see, Im not overriding ENV in webpack config using the webpack.DefinePlugin plugin.
So why my process.env is EMPTY?
When I start the app with npm start, the process.env is normally filled and process.env.NODE_ENV is set to development.
Thank you for any help!