It would be a week or till I can get some brewers nutrient is there any food substitute I can use, apples, rice, sweetcorn, apple juice, tomato paste etc?
Unlikely and it will cost a hell of lot more chasing down the ingredients to put together your own yeast nutrients. I have been brewing for 25 year and have never used them. I had problems brewing when I first started but those were rookie mistakes. If you have enough yeast and wort and oxygen, there shouldn't be anything that stops your yeast from fermenting. Having said that, there are instances that I would use them, like super high gravity beers. I did use them in my winery when I had very ripe grapes. I would put pounds of that stuff in my must (I was fermenting multiple tons at a time).
This list is from Beer and Brewing magazine. You can actually buy all this stuff separately but it probably isn't what you wanted to do. Just pitch enough viable yeast and you'll be fine!
- Diammonium phosphate (DAP) is a water-soluble salt that is often included in plant fertilizer to increase the pH of soil. It also delivers valuable nitrogen and phosphate to yeast cells. Wort is generally rich in nitrogen, but a little supplementation can help high-gravity beers complete fermentation. Phosphates also help ensure smooth fermentation of worts that contain large portions of non-malt adjuncts.
- Amino acids are necessary for creating proteins and for reproduction. Yeasts can actually make most of their own amino acids, but there are a handful, termed essential amino acids, that cells must pull in from the wort they’re in. If wort happens not to have enough for one reason or another, a little boost of yeast nutrient can help keep your yeast cells happy.
- Vitamins and minerals of all kinds—biotin, pantothenic acid, calcium, magnesium, potassium, and many others—are necessary for the reactions that create the compounds yeasts need to do their job. They also serve as catalysts in many of the reactions that take place during fermentation, and some even aid in flocculation and cell wall preservation.
- Zinc, which falls under the mineral umbrella is one of the less common essential minerals found naturally in all-malt wort. Zinc plays a vital role in the production of ethanol, which we can all agree is pretty key to the whole beer thing.
- Yeast ghosts, or yeast hulls, are basically the water-insoluble skeletons of dead yeast cells, and they’re included in many nutrient formulations, as well as available on their own. Live yeast cells cannibalize these dead cells and feed off the nutrients they contain. Gross, eh?
I add a tablespoon of dry baking yeast to the boil when I'm preparing a starter. It's cheap (I'm into baking, too, so I buy relatively large cans of baking yeast anyway). Experience indicates it's also sufficient for the purpose. I have also heard of people boiling grape seeds for the nutrient. At my LHBS I once bought a "wine yeast nutrient", which was likely DAP (nothing specific on the package about it), but I stopped using it, as I suspected it gave my beers some metallic flavour. Btw yeast nutrient is only good when you add it early. Adding nutrient to a beer that is 50% through fermentation is mostly pointless. Also, when faced with a choice "prepare a bigger starter" vs "add yeast nutrient" (for a big beer), I'd suggest going for the bigger starter.