How to Fill a Sausage Without Air Pockets or Burst Casings

Why sausages burst or trap air when you fill them and how to stop it before the first one comes out.

Sausages burst when the casing takes too much pressure at one spot, and they get air pockets when air is trapped in the mix before it reaches the casing. Both come down to how the filler is loaded and how the casing is handled, so almost all of the fix happens before the first sausage comes out.

Mix until it is smooth and even

A loose, lumpy mix holds air. When clumps of meat go into the filler they leave gaps between them, and the gaps travel down to the nozzle and end up as bubbles in the casing. Mix until the meat turns sticky and holds together, with no dry seasoning left and no pooled liquid in the bowl. Then press the mix down in the bowl with your hand to push out the loose air before you carry it to the filler.

Pack the filler solid to the nozzle

Add the mix a handful at a time and press each handful down firmly into the corners. Keep going until the filler is full. Before the casing goes on, bring the mix up until you can see it at the very tip of the nozzle. An empty nozzle means the first stretch of casing fills with air, and that air becomes the first bubble you have to chase.

Feed at an even speed

Fill at one steady pace. If you start and stop or speed up and slow down, the mix comes out in surges, and a surge can leave a loose spot or a small gap. Use one hand to work the filler and the other to hold the casing lightly as it slides off the nozzle. Let the mix push the casing along and keep just enough drag in your fingers that it fills evenly. If you grip the casing too tightly it fills tight and bursts, and if you let go completely it fills loose.

Do not over-fill

A casing stretched to its limit has no give left. It splits when you twist the links and it can split again when the meat heats in the pan. Aim for a sausage that is full and firm but still has a little spring when you press it with a finger. If the casing looks stretched thin and tight, fill the next length a touch looser.

Get the casing ready

A dry casing grabs the nozzle and tears, and a torn or weak casing is where many bursts start. Natural casings come packed in salt and need a rinse and a soak in water until they are soft and pliable. Flush water through the casing to wash out the salt and to find any holes before you fill. Collagen casings are uniform in size and usually need little or no soaking, so follow the instructions on the pack.

Natural casings stretch more and vary more from one piece to the next, while collagen has less stretch and is less forgiving if you over-fill. Wet the nozzle too because a damp nozzle lets the casing slide on without catching.

Prick the bubbles

Even a careful fill leaves the odd bubble. Prick it with a fine pin or a sausage pricker while the sausage is still in one long length, and gently push the air along toward the open end. Prick only where you can see air and keep the holes small.

Rest before you twist

Fill the whole length first and lay it in a loose coil without twisting as you go. Let the coil sit for a few minutes so the mix settles and the casing relaxes, then check along it for bubbles and prick any you find. Twist into links after that, turning each link in the opposite direction to the one before so the twists stay put. A short chill before twisting also helps the links hold their shape.

If this happens, do this

•         The casing splits while filling:  Stop and ease off the pressure, then check that you are not over-filling. Look at the casing for a weak spot or a hole.

•         There are bubbles under the casing: Prick them and push the air toward the open end. Next time pack the filler harder and mix until the meat is sticky.

•         There is a big air gap at the start of the sausage: The nozzle was empty when you fitted the casing. Bring the mix to the tip first and start again.

•         The casing bursts when you twist: The sausage is filled too tight. Squeeze some mix along toward the empty end, twist again and fill looser on the next length.

•         The casing keeps tearing at the nozzle: It is probably too dry. Wet the casing and the nozzle, and check the edge of the nozzle for a nick.

•         The links split in the pan: Cook them over a gentler heat and turn them often, and fill a little looser next time.

•         The mix looks pasty and smeared as it comes out: It has warmed up. Chill it first.