Brew in a Bag (BIAB) is one of the simplest ways to produce excellent beers using less equipment than a standard 3-vessel system. People using this method usually use only one pot, or all-in-one systems (like the Mash & Boil or Anvil Foundry) for the mashing of grain and the boiling of the wort.
The first thing you should do is size up your vessel. You will need to know the depth and the outer diameter of the vessel so that you can get the right size bag. Also consider the size of the holes in the bag, called Microns, when purchasing. The larger the Micron number, the larger the holes in the bag. For example, brewers with recirculating pumps should use 400 microns, while those using a standard kettle or electric system without a pump can use 200 micron bags. After you have the bag, make sure to clean it with some hot water and something like PHO-BW to make sure it’s ready for use.
Now you have everything you need to get started, except the grain! Because you’ll be using a bag to contain your mash, you can use a finer setting on your mill when crushing the grist. This may result in a slightly higher efficiency, so use the first couple of brews with a new bag to learn how it will change your brewing habits. If you’re new to brewing, this means you might have slightly stronger beer than you originally anticipated, but you’ll learn how to make adjustments as you continue to use the bag.
Next step is to mash in. You’ll need to use a Mash Calculator like this one to determine your water temperature. Enter the temperature of the grain and the total number of pounds in your grist, then do the math for what your quarts/pound are. For example, if you’re doing a full volume mash for a 5 gallon batch, you would probably use between 6-7 gallons or so. If your grist is 11 pounds of grain, the quarts/pound would be 2.18 (assuming 6 gallons). Then just enter your target mash temperature and the calculator will tell you the temperature to heat the water to before you add the grain. Add the grain slowly and stir well to make sure you don’t have any dough balls in your mash.
After the mash, and what is probably the biggest advantage of the BIAB method, you can squeeze the bag to get additional wort out of the grain and into your kettle! If using an electric kettle, set it to the boiling temperature while you squeeze the bag to save some time. Just be careful because that bag will be hot! Heat gloves are absolutely necessary for anyone squeezing the grain bag. This will highly reduce the losses for grain absorption and may also help bump up the efficiency of your brew. If you’re still a little short on volume after squeezing the bag, rinsing the grain with some water and squeezing again can help, or adding additional water to the kettle can achieve the same goal. Depending on your system, you might lose ½ to 1 gallon per hour of boiling, or maybe more! Make sure to account for these losses before the boil.
The rest of the brewing process doesn’t change; the wort is then boiled, chilled, and transferred to a fermentation vessel of choice where yeast is pitched. The Bag can then be dumped (see if any of your neighbors have chickens – they love spent grain), rinsed and set somewhere to dry and use again. There isn’t necessarily a need to wash the bag after each use, a thorough rinsing to get all the grain particles off should suffice. With proper care you can use your bag many times over.
Stop into Philly Homebrew Outlet to have any questions about the Brew In A Bag method answered, and (especially on Sundays at the Jersey Store) possibly see a brew in progress!