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I'm realativly new to AG (8 batches) but here's my process...
After mashing is complete I do a mash-out (which I'm told is not necessary but I still do) which means I raise the temp of the mash to 168 and let it rest for 10 minutes. Then I recirculate the mash draining it very slowly and returning the drained wort to the top of the mash. This recirculation is call the vorlauf. You need to vorlauf until your wort runs clear and there are no signs of any solid matter in your wort. Now it's time to sparge! Sparging is draining your wort into your boil pot (again) very slowly until you have collected the amount of wort you plan to boil - typically 6.5 to 7 gallons for a 5+ gallon batch (or you have reached a SG of 1.008) which ever comes first. At the same time you are draining you replenish the wort on top, never letting your grain bed be exposed) with 168 degree (not over 170) water. The replentishment of water on top of the grain bed is sparging (or sprinkling). This is the challanging part...you want to keep between 1 and 2 inches of water on top of the grain bed at all times, so you have to match the draining flow with the sparging (incoming) flow. I've read that sparging should take between 45 and 60 minutes but I drag mine out to a little over and hour.
The method I've described is called "fly sparging". There is also a method called "batch sparging". I've been told you get better efficiency with fly sparging (don't start a war over this statement!!), but I've never done batch sparging so maybe someone else can describe that. I'd like to see that described ;D
For practice you might want to play with just plain water and see what the flow rate looks like for a 60 minute sparge.
thanks for the info,
so after vorlauf the wort clearing is the indicator to start collecting for the boil. should I be looking for a starting gravity after vorlauf or just collect run off until the gravity falls to 1.008.
Below that, Tannins are being extracted, from the hulls, during the sparge and will cause undesirable flavors in the finished beer.
Batch sparging is where you runoff the mash, add a new volume of water to the mash, rest to extract more sugars, and runoff again.
Typically, you would runoff all the water in to the kettle and then either boil or add DME to increase gravity, or dilute to lower, to desired level.
Another version is Parti-Gyle and this is where the first runoff is collected seperate from the second (and/or third) runoff to make different beer from the same mash.
An excellent source for brewery calculations is Designing Great Beers by Ray Daniels. It is very technical tho'.
I'm no expert but per John Palmer's book - How To Brew;
Continuous Sparging usually results in better extractions. The wort is re-circulated and drained until about an inch of wort remains above the grain bed. The sparge water is gently added, as necessary, to keep the fluid at least at that level. The goal is to gradually replace the wort with the water, stopping the sparge when the gravity is 1.008 or when enough wort has been collected, whichever comes first. This method demands more attention by the brewer, but can produce a higher yield.
The simple answer to your qeustion"should I be looking for a starting gravity after vorlauf or just collect run off until the gravity falls to 1.008": no...just run off slowly (can't say that enough ) until you hit 1.008 OR you have collected between 6.5 and 7 gallons (I'm assuming 5 gallons batch) which ever happens first. Of course if you hit 1.008 and you don't have enough wort in your boil pot you need to top off with water to accomodate the evaporation during boil.
The reality of it is that Fly Sparging does provide for better efficiency (although many will debate this) but, batch sparging is a simplified method and the loss of efficiency can be countered by a miniscule amount of additional grain (Ounces).
There are a number of methods by which to extract sugars to varied degrees, ranging from the simple to the very complex. But commonplace amongst homebrewers are the batch and the fly.