BIAB is the ultimate simplification of the all grain brewing process. There is just one special piece of equipment you need. The BIAB Bag.
There are many different forms of bags. The best one in my opinion is the truncated cone bag. It fits perfectly in your kettle and has just the right amount of fabric. You can throw it in the washing machine or rinse after use. Then hang it to dry and forget until the next brew day.
It is not the easiest bag to build. But it is definitely the best to brew with. I already made about 10 of these bags. The first one i built was hideous but is still in use today and will be for many more years. Just keep them away from sharp objects and take care when mixing the mash.
Are you ready to build one yourself?
Sewing Machine [Amazon]
If you don’t own one yourself, ask friends or relatives. Even a very old model will do. Use a 80 or 100 standard or microtex needle. Don’t use jeans needles, they will damage the voile.
Voile Fabric [Amazon]
You can buy this kind of fabric in the hardware store, ikea or online. You can find it in the window blinds section. I always use the one made out of polyester. It should have about 30 – 35 woven strings per cm.
Polyester Thread [Amazon]
Use normal thickness 80-100Nm white polyester thread. I made the mistake and used extra thick and strong thread for my first bags, that just wrinkled the voile and made sewing a lot more difficult. Don’t use cotton, it will disintegrate over time.
Tape Measure [Amazon]
Take anything long enough ~3m
Take a water soluble pen that will easily wash away.
The small pins with the colored heads are best.
Mine were sharp enough to just glide trough the voile fabric without cutting.
Lashing Straps [Amazon]
For reinforcements and to add handles to your bag. You can buy it new or recycle it from load securing straps.
Start with measuring your kettle depth and upper/lower diameter. Enter the measurements into the calculator. The pot i use in this example has a diameter of 50cm and a depth of 48cm.
Click on the calculate button. This will give you a lot of numbers, don’t despair they will become clear soon.
Take the number next to the letter l. Write it down somewhere. This is about the length of fabric you will need for your bag. For my bag, the fabric has to be about 235cm long.
Double the number next to the letter h. Now you know how wide your fabric has to be. Most fabric comes at about 1.5 – 2m wide. So it should be good for a very deep pot. My piece of fabric has to be about 120cm wide.
Now if you don’t already have it, you can go and buy the fabric. For my pot i will need about 235x120cm.
Now that you got all the fabric you need you can start measuring. You need a large flat surface. Start by laying the fabric flat on the ground. Use some tape to stick the fabric to the ground so it can not move around.
From the top left corner measure length b and mark it down on the ground. This is where the pivoting point of your drawing string will be.
Knot a loop into the end of a piece of string. Get someone to hold the other end on the measured pivoting point. Put a pen into the loop and you can draw a nice arc on the fabric.
Repeat this for length a from the same pivoting point.
Now measure length l from the top left corner to the right. This will be the final length of your 2 arcs.
With the help of your string, draw a circle with the radius r2 on the leftover fabric. This will be the bottom of your bag.
I recommend to always measure twice before putting the scissors to the fabric. If you are satisfied you can start cutting the fabric. Start along the two arcs and the connected ends of those two arcs. Don’t forget to cut out the circle.
Congratulations, you finished cutting all the fabric.
With the help of your pins, construct the frustum out of the two pieces of fabric. You will get an idea how to sew everything together.
Now comes the hard part. Start slowly, it is difficult to go back once you got something wrong.
Start by stitching the two outside sides of the tube together. Let the sewing machine transport the material. Don’t rip or try to help the machine transport the fabric in any way.
This is the first part of the french seam. The voile fabric is very fragile and it can rip out if you don’t leave a seam allowance of at least 0.5cm.
When you are finished with the tube, you can start connecting the circle. Leave the same allowance of at least 0.5cm. Don’t worry if you take a little too much fabric, you can always cut it away with scissors.
Now that you finished the first seam you should have a good idea of the completed bag.
Turn the whole tube inside out. Carefully flatten the inverted seam. You can use a clothes iron on low setting but i always do it without. Again, sew the tube and the bottom, this time with a allowance of 0.7cm. This will hide the first seam. The bag should look almost complete now.
There is one final seam you can make by stitching the whole seam allowance to the tube.
If your seams look ugly, don’t worry, they just need to be strong.
To make the bag easy to lift and strong, i always add grosgrain around the upper end. Some people just add a drawstring tube, but that’s not enough for me.
This should be a very easy step to do after your sewing practice with the bag.
Fold the voile fabric once to hide the rough edge and pin some grosgrain around the whole length. Don’t forget to add handles. I always add 4.
Sew the grosgrain to the voile, first around the top. Then once more around the bottom of the grosgrain.
That’s it, congratulations! Admire your work and put that bag in the washing machine before the first use.