Here's a quick way to make Raisin Yeast Nutrient for your home brews. Now generally these aren't use in beer brewing, but can be. Mainly raisin yeast nutrients are used with cider, mead and wine making.
Some brewers enjoy the added depth of flavor raisins bring to the party, but as well as giving the yeast more to work with, a raisin yeast nutrient is often felt to improve the bouquet/smell of the finished product.
I have tried raisin yeast nutrients on several differing home brews and to be totally honest I don't find much difference with yeast cultivation of flavor changes. Maybe I just don't have the pallet other brewers do, but by all means give it a try and let me know how you get on. :)
To make the raisin nutrient get about 100g of raisins in a saucepan with water that covers them by an inch or so. Bring them to the boil and simmer till they are plump and easy to mash, mash to a paste and make a raisin tea, depending on the wort/brew it is being added to you may wish to remove excess raisins.
Happy brewing.
Cheers :)