You can get a Sourdough Starter happening well enough to make bread in 7 days or less. The trick is feeding the fresh starter the right amount at the right time.
The measurements start small, but grow quickly. This is because sourdough starter is a living thing, and as it grows, so too does its appetite. You'll be doubling the size of the sourdough starter every couple of days, so make allowances for this with your storage container.
I use a clear plastic container, about 1 to 1.5 litres, with a clip on or loose fitting lid. If it's 'clip on' type, leave it loose at all times when storing sourdough starter, so it can breathe. It doesn't breathe much though - even if you clip the lid shut, the starter will take about a week to consume it's own volume of air.
Following is the rapid version of the recipe - underneath is the explanation, for when you get into the detail.
QUICK SOURDOUGH STARTER RECIPE:
In your container, mix one dessertspoon of wholegrain flour to one dessertspoon of unsweetened pineapple juice.
Repeat Day 1. During cold weather, allow the mixture to rest another day before proceeding to the next step.
Add two dessertspoons of wholegrain flour and two of pineapple juice and stir them into the mixture.
Repeat day three. In colder weather, allow the mixture to rest an extra day before proceeding to the next step.
Add two more dessertspoons of wholegrain flour and two of pineapple juice. Stir into the mixture.
Repeat day 5. Don't move on till you have a veryy bubbly mixture.
Your starter is now built. It is not yet strong enough to raise a loaf, but in time, it will be!
During this first stage, your starter grows best out of the fridge. Room temperature is fine. Once it is built, keep it in the fridge.
Please Note: For the first six weeks, use semi leaven recipes to make bread. After that, you can proceed to pure sourdough recipes, as your starter will have established a viable culture by this time.
Semi leaven sourdough recipes require a small amount of yeast (about 1/2 to 1 % of powdered yeast against the flour weight) to help with the rise. The more established your starter becomes, the less yeast you will need. Eventually, you won't need yeast at all.
When using yeast, it is important not to contaminate the starter. Keep the lid on the starter while making dough with yeast. Don't put yeast in the starter itself.
NOW FOR THE DETAIL:
Why six weeks?
Sourdough starter is a living thing. Inside that bubbling jar of goodness is a rather complex and beautiful process which won't be hurried. In the same way that a child grows every day, but still takes about thirteen years to achieve physical maturity, sourdough starter needs about six weeks before it is viable.
Why Pineapple Juice?
Pineapple juice has the right ph to assist the fermentation process. It also supports helpful bacteria in sourdough culture while holding harmful bacteria to keep their place in the process, rather than taking it over. The process of fermenetation involves a kind of relay race of bacterialogical activity, where one type of bacteria pass the baton to another when their job is complete. Pineapple juice keeps things ticking over while this natural process happens, and stops it from getting sidetracked.
Once fermentation has been established, the ph in the starter does not require pineapple juice, so water is fine. The starter actually consumes the fruit sugars, so there really isn't a real reason not to use juice in the initial fermentation process. Just make sure it is unsweetened, as you don't need sucrose in the ferment.
Why wholegrain flour?
Wholegrain flours contain more natural yeasts. Whether you use wheat, rye, spelt, khorosan or another type of grain, the flour should be truly wholegrain, not wholemeal. Stone or hammer milling is best, as these forms of milling do not separate the various parts of the grain from each other in the milling process, as occurs when roller milling is used.
Once fermentation has been established, white flours can be used. Grains can also be changed from one to another, or new types cultivated from other grains.
How do I use and maintain the sourdough starter?
You will have built about 600mls of liquid sourdough starter if you have followed the recipe above. Most of the recipes in the site need 300mls of liquid starter.
Use half of the starter in your recipe of choice, and feed to replenish - which means 150 grams of flour to 150 mls of water. Feeding should be done at the same time as you make the dough for your next batch of bread.
You will need to feed the starter approximately once a week. If you are making bread less often, then pour off half and feed anyway. Liquid starter can easily ferment too much, making it more alcoholic. In this state it won't make good bread.