High quality hydrolysed yeast liquid that has received somewhat of a cult follow over the years.
Having been absent from the market for quite a while I can confidently say this will be available from OptiBaits long term.
Most people use it between 10-25ml per kg of base mix. I personally like it at 10ml especially if used alongside powdered yeasts.
Can also be used as other liquid foods would be (in bags, soaking baits etc)