How to vent and tap a cask properly

Last updated: 29 June 2026

Most pubs tap a cask wrong the first time, and it costs them three to five pints of product before they even pour a pint for a customer. I’ve watched it happen dozens of times: a new member of staff stabs a tap into a cask blind, the vent hole isn’t open, pressure builds, and suddenly you’ve got ale pouring across the cellar floor. Then the same licensee wonders why their stock numbers don’t match till sales. The truth is, venting and tapping a cask is a two-minute job that directly affects both your costs and your pour quality—yet most pubs treat it as something anyone can muddle through.

This guide walks you through the exact sequence I use in my cellar, the reason each step matters, and the one mistake that costs you money every single time.

Why venting matters before tapping

A cask under pressure will spray ale across your cellar the moment the tap breaks the seal. Most licensees understand this in theory. But what they miss is that venting isn’t just damage control—it’s how you avoid losing product the moment you open the cask.

When a cask is sealed, the gas inside (usually CO₂ or nitrogen, depending on the product) is under pressure. That pressure keeps the beer fresh and the cask intact during transport. The moment you want to draw product, that pressure becomes your enemy. If you tap the cask without opening a vent hole first, the pressure will force beer out of the tap hole faster than you can control it, and you’ll waste anything from half a pint to two pints before the pressure equalises.

But here’s the part most pubs get wrong: the vent hole isn’t optional, and it isn’t a quick jab with a spike. A proper vent hole allows air to enter the cask as beer leaves, which maintains even pressure and prevents vacuum formation. Without it, you get a partial vacuum inside the cask, which slows the pour, strains your lines, and sometimes stops the flow altogether.

Think of it like pouring wine from a bottle. If you don’t let air in, the flow slows and glugs. Same principle. The difference is that a cask holds 36 to 288 litres, so the pressure is higher and the consequences are messier.

Step-by-step: how to vent a cask

What you need

• A cask vent (also called a spile or vent peg) — plastic or metal, sized to fit your cask
• A small hammer or mallet (light tap only, not a full swing)
• A cloth to catch any spillage during venting
• The cask positioned on a proper cradle or stillage, not on the floor

The process

Step 1: Position the cask correctly. The cask should be on a cradle with the flat top facing you and slightly tilted towards the tap side (if the cask has already been tapped). Never work with a cask on the floor or balanced on uneven surfaces—you’ll lose your grip, and the cask will roll.

Step 2: Locate the vent hole. On most UK ale casks, there’s a small hole on the opposite end from where the tap will go. On some casks, especially if this is a rebirth (already in use), the vent hole is already marked. If not, it’s typically on the top surface near the edge of the end you’re not tapping.

Step 3: Place the vent. Position your plastic or metal vent peg over the hole. Hold it steady with one hand. With a light tap from a small hammer, drive the vent into the hole just enough so it’s snug but not hammered in hard. You want it to stay in place, not be driven deep into the cask wall.

Step 4: Listen and watch. As you vent, you’ll often hear a small hiss of gas escaping. This is normal and means pressure is releasing. Some ales will bubble or seep slightly around the vent—catch this with a cloth. This isn’t a sign you’ve done it wrong; it’s proof the vent is working.

Step 5: Check the vent is secure. Give the vent a gentle tug. It should sit firmly in the hole. If it’s loose, you haven’t vented properly, and you’ll get pressure buildup when you tap.

Step-by-step: how to tap a cask

What you need

• A cask tap (the metal or plastic fitting that screws or pushes into the cask)
• A small hammer or mallet
• A cloth or bucket to catch initial spillage
• Your cask already vented and positioned

The process

Step 1: Choose the tap hole. This is always on the flat end opposite the vent. Look for a small circle or dimple marked on the top of the cask. This is the tap hole. If you can’t see a mark, it’s typically at the widest point of the flat end, roughly in the centre.

Step 2: Position the tap. Place the tap against the hole. Some taps have a pointed metal spike (screwdriver-style), others are blunt and wider. Match the tap to the cask type. Never use the wrong size or type of tap—it will leak or split the cask.

Step 3: Drive the tap in gently. With a small hammer, tap the top of the tap fitting with light, controlled hits. Do not swing hard. You’re driving the tap gradually into the wood or plastic cask wall, not smashing it. Usually six to ten light taps is enough. You’ll feel resistance as the tap seats into the hole.

Step 4: Stop when the tap is seated. Once the tap is firm and won’t move with a gentle push, stop. Overtapping can crack the cask or damage the internal seal. You should see the tap sitting flush or slightly proud of the cask surface.

Step 5: Check for leaks. With the vent in place, gently place a cup or cloth under the tap opening. If the cask is properly vented and the tap is seated correctly, you should see no drips. If beer is seeping around the tap, the tap isn’t seated properly—remove it carefully and redo it.

Step 6: Connect your line. Once the tap is confirmed dry, connect your beer line (if using a direct draw) or attach your cask connector. This is now safe to move into position for service.

Common mistakes that waste beer

Tapping without venting

This is the most common mistake. You tap the cask, pressure releases suddenly, and two to five pints spray across the cellar floor. You clean it up, and the till reconciliation is never quite right. Always vent before tapping, full stop.

Venting in the wrong place

I’ve seen staff put a vent hole in the side of a cask thinking it doesn’t matter. It does. The vent hole should be on the flat top surface, on the opposite end from the tap. Side holes create uneven pressure and often don’t stay sealed properly, especially if the cask is moving or settling.

Overtapping or using the wrong tap

Cask walls are not infinitely strong. If you hammer a tap too hard or use a tap that’s the wrong diameter, you’ll split the wood or puncture the seal inside. This leads to slow leaks you might not notice until the cask is half-empty and you’re wondering where the beer went. Spirits hide losses in over-pouring (a free-poured 25ml is often 32-35ml), draught hides it in poor cellar temperature and bad line cleaning waste, and most stock ‘theft’ is actually measurement error and forgotten wastage.

Not recording the tap date

This is where most pubs lose control of stock. You tap a cask on Monday, but by Friday no one can remember which cask it was or when you opened it. Then two weeks later you’re trying to reconcile a partial cask against till data and it’s impossible. Write the tap date on the cask in permanent marker, or better yet, log it in a simple stock app like the StockTap pub stock app as soon as the tap goes in. This takes 30 seconds and it’s the difference between knowing your numbers and guessing.

Leaving a cask vent open too long

Once the cask is vented and tapped, the vent hole does its job by letting air in as beer comes out. But if you leave the cask sitting with the vent hole open and nothing coming out, you’ll oxidise the beer. The vent should stay in place and sealed. Only remove it if you need to re-vent a cask that’s been sitting unused for more than a few days (which is rare).

How to track cask stock properly

Venting and tapping a cask correctly keeps the beer clean and prevents spillage. But it’s only half the job. The other half is knowing what came out of that cask and whether your till matches reality.

The most effective way to control cask stock is to dip every cask and partial keg, weigh open spirit bottles, and reconcile against till data the same day. This catches losses before they spiral. In my own pub, I was running stock on a tangle of spreadsheets and still losing track of partial kegs and spirit measures. I built a simple count routine around a dipstick and a set of scales, and the weekly variance went from guesswork to a number I could trust within a fortnight.

Here’s what I do every Tuesday morning:

• Dip every cask and partial keg — use a simple plastic dipstick, measure the depth of beer, record it by cask name.
• Weigh open spirit bottles — a small set of scales takes 60 seconds per bottle.
• Note any spillage or waste — if a line burst or a customer spilled a pint, write it down. Don’t guess.
• Pull till data for the same period — how many pints of ale did the till say you sold?
• Reconcile same day — if you sold 47 pints according to till but the cask shows only 44 pints used, you’ve got a 3-pint variance. Investigate that day, not three weeks later when you’ve forgotten what happened.

Most pubs that move from a messy spreadsheet to a disciplined count claw back 1-2 GP points within a couple of months, and a 1% stock loss on wet sales quietly costs a typical pub £3,000–£5,000 a year. That’s worth 15 minutes a week.

SmartPubTools has built a cellar management feature into their stock app specifically because they know most pubs don’t track cask dips at all. But even a paper notebook works if you’re consistent.

When to call the brewery

If you follow the steps above and the cask is leaking around the tap, or if the internal seal is damaged (beer seeping into the wood rather than coming out of the tap), that’s a faulty cask. Stop using it immediately and contact your brewery or supplier. They’ll replace it.

But first, check three things: Is the tap the right size for this cask? Have you overtapped it? Is the vent actually open and secure? Most “faulty” casks are user error. Only after you’ve ruled that out should you blame the cask.

If a cask has been sitting tapped for more than five days without being moved and the beer inside has started to oxidise (tastes flat or off), don’t try to save it. Mark it as waste, record it in your stock log, and move on. The cost of writing off a few pints is less than the reputation damage of serving poor beer.