The CO2 delivery didn't show up. Again. You've got a brite tank to purge, a canning run scheduled for tomorrow morning, and the gas supplier just told you allocation is tight for the rest of the month. Every brewer who worked through 2022 remembers that phone call, and plenty are still getting a version of it.

Here's the thing a lot of small breweries miss: about half of what you use CO2 for doesn't need CO2 at all. Purging tanks, pushing beer between vessels, blanketing, pre-purging kegs and cans, running the keg washer. Those jobs need an inert gas, not carbon dioxide specifically. A nitrogen generator for breweries makes that gas on site from the same compressed air you already run, and it doesn't care what the gas supplier's truck is doing.

This is a spoke off our main brewery air guide, Compressed Air for Breweries: What You Actually Need. Read that one for the whole air system. This one is just about nitrogen.

Where nitrogen replaces CO2 in the brewhouse

Walk the process and count the places you are burning CO2 for a job that only needs oxygen gone.

Tank purging. After CIP, a fermenter or brite tank is full of air. You push it out with gas before transfer so the beer never touches oxygen. This is the single largest CO2 consumer in most breweries, and nitrogen does it just as well. The oxygen leaves either way.

Transfers and pushing. Moving beer from fermenter to brite, or brite to the filler, with top pressure. Nitrogen works here for anything that is not finished, carbonated beer, and even then a nitrogen/CO2 blend is common.

Blanketing. Holding a headspace over beer or wort in a tank that isn't full. Nitrogen is less soluble than CO2, so it doesn't change carbonation the way a CO2 blanket will over a long hold.

Keg and can pre-purge. The keg washer's final purge and the can pre-purge on the filler both just need an inert gas to displace air. Some fillers also use nitrogen for the headspace dose right before the seamer, which is a small dose, but it happens on every single can.

Lab and QA. Dissolved oxygen meters, sample purging, and some analytical gear run on nitrogen.

What stays on CO2: actual carbonation, and packaging steps where CO2 is what you want in the beer. Nitro beers are their own conversation and use a 70/30 nitrogen/CO2 blend on the dispense side, which a generator can also feed.

How the generator works

Air is 78 percent nitrogen. A nitrogen generator separates it from the oxygen and everything else. There are two ways to do that, and the choice matters for a brewery.

PSA (pressure swing adsorption)

Two towers filled with carbon molecular sieve. Compressed air goes into tower one, the sieve grabs oxygen, CO2 and moisture, and nitrogen passes through. When the sieve loads up, the system swaps to tower two and vents tower one to regenerate. PSA units reach 99.9 to 99.999 percent purity and are the right choice when you want very low residual oxygen. The trade-off is that higher purity costs more air: as purity goes up, more of your compressed air gets vented during regeneration.

Membrane

A bundle of hollow polymer fibers. Air goes in one end, oxygen and water vapor permeate out through the fiber walls faster than nitrogen does, and enriched nitrogen comes out the other end. No moving parts, no towers cycling, very quiet. Membrane units are simpler and cheaper up front but top out around 99.5 percent purity in practice, and they are less efficient than PSA at the high-purity end. The Nano NMG membrane generator we carry sits in this category, and for a brewery that wants nitrogen for purging and blanketing it is often the right size and price.

What purity does a brewery actually need?

This is where breweries overbuy. Most brewers run tank purging, blanketing and keg work at 99.5 to 99.9 percent nitrogen, and a growing number are comfortable at 99.99 percent for packaging. A 99.5 percent stream is 0.5 percent oxygen, or 5,000 ppm. That sounds like a lot until you remember the tank you are purging started at 210,000 ppm. The purge is doing its job either way; what changes is how many volumes of gas it takes to get the headspace where you want it.

For canning and the can headspace dose, tighter is better because the gas is going straight over finished beer. That is where 99.99 percent PSA earns its keep. For everything upstream, membrane-grade nitrogen is fine and costs less to make.

One note on units: brewers think in dissolved oxygen, in parts per billion. Generator purity is specified in parts per million of oxygen in the gas stream. A 99.99 percent unit is 100 ppm O2 in the gas. Those are different measurements, and the gas number does not translate directly to DO in the package.

Sizing: think in SCFH, not tank volume

Nitrogen generators are rated in standard cubic feet per hour (SCFH). To size one, list every nitrogen use, the flow each one pulls, and which ones can happen at the same time. A brewery's problem is that demand is spiky: nothing for two hours, then a 30 barrel brite tank purge that wants a lot of gas in 20 minutes.

Two ways to handle the spike. Size the generator for peak flow, which is expensive, or size it for average flow and add a nitrogen receiver tank so it can fill the buffer between purges. The second approach is almost always the right one for a brewery. A generator making 500 SCFH into a 240 gallon receiver at 120 psi can cover a purge that momentarily wants three times the generator's output.

Small craft systems on the market run from roughly 200 SCFH up to about 2,200 SCFH, and that range covers most breweries under 20,000 barrels. A rough starting point for a 10 to 15 barrel brewhouse doing tank purging and keg work is 300 to 600 SCFH at 99.5 percent with a receiver. Add canning headspace and you either bump the flow or split it: a membrane unit for the cellar and a small PSA for the packaging line.

The compressor behind the generator

A nitrogen generator is only as good as the air feeding it, and it eats a lot of air. At 99.5 percent, a membrane unit consumes about three to four cubic feet of compressed air for every cubic foot of nitrogen it produces. A 500 SCFH generator wants 25 to 35 CFM of clean, dry compressed air, continuously while it runs. That is a 7.5 to 10 hp compressor's worth of air just for nitrogen, on top of whatever your brewhouse already uses for valves, the filler and the keg line.

The air also has to be treated. Oil and water destroy carbon molecular sieve and foul membrane fibers, so every generator manufacturer specifies an inlet train: a refrigerated dryer to a 38 F dew point, then particulate, coalescing and activated carbon filters, in that order. Oil-free compressed air is the cleanest starting point, and it is what the brewery hub recommends for any air that can end up in contact with product. Our oil-free air compressors and air filters collections cover the front end, and the Nano Purification collection has the generators, dryers and filter sets built to go together. Our general nitrogen generator guide has more on the technology if you want it.

Do the math before you buy. If your existing compressor is a 5 hp piston unit that is already busy, adding a nitrogen generator to it will not go well. Plan the compressor and the generator as one system.

Does it pay?

CO2 cost is the driver, and it varies wildly by region. In much of the country bulk CO2 still runs under 25 cents a pound, but breweries in tight markets have been quoted five times that during shortages, and delivery fees, tank rental and hazmat charges sit on top of the per-pound price. A brewery that shifts purging, transfer and keg work to nitrogen typically cuts CO2 purchases by 30 to 50 percent. At 10,000 pounds of CO2 a year, that is 3,000 to 5,000 pounds you are not buying, plus fewer deliveries and one less thing that can stop production.

Generated nitrogen costs whatever the electricity for the compressor costs, plus filter elements and a sieve or membrane rebuild every several years. Most breweries we talk to pencil out a two to four year payback on the generator itself, faster if they were paying shortage pricing or renting a bulk CO2 tank.

The number that does not show up on the spreadsheet is the canning run that happened on schedule because you were not waiting on a truck.

Mistakes breweries make with nitrogen

Buying 99.999 percent for everything. Ultra-high purity roughly doubles the air consumption compared to 99.5 percent. Use it where it matters (packaging, lab) and run the cellar on membrane-grade gas.

No receiver. Without a buffer tank the generator has to be sized for the biggest purge, and it sits idle the rest of the day. A receiver lets you buy a smaller generator.

Feeding it wet air. Skipping the dryer or running past the filter change interval kills the sieve or the membrane. The inlet train is not optional.

Forgetting the compressor. The generator's air demand is real and continuous. Confirm you have the CFM before you sign.

Running nitrogen into carbonated beer without thinking. Nitrogen is far less soluble than CO2, so pushing finished beer with pure N2 at pressure can strip carbonation. Use a blend or CO2 for that step.

Frequently Asked Questions

Can I purge my fermenters and brite tanks with nitrogen instead of CO2?

Yes. Purging is about removing oxygen, and nitrogen does that as well as CO2. Most breweries run tank purging at 99.5 to 99.9 percent nitrogen. Keep CO2 for carbonation and for pushing finished carbonated beer, or use a blend.

What purity nitrogen does a brewery need?

99.5 to 99.9 percent covers tank purging, blanketing, transfers and keg washing. Canning headspace and lab use are where breweries step up to 99.99 percent, usually with a PSA unit.

How big a compressor does a nitrogen generator need?

Plan on three to four CFM of compressed air per SCFM of nitrogen at 99.5 percent, more at higher purity. A 500 SCFH generator wants roughly 25 to 35 CFM of clean, dry air on top of your existing brewhouse demand.

Membrane or PSA for a small brewery?

Membrane for the cellar: purging, blanketing, keg washer. It is quiet, simple, and cheap to run at 99.5 percent. PSA when you need very low oxygen in the gas, mainly on the packaging line.

Will nitrogen change my beer?

Not when it is used for purging and blanketing. Nitrogen is barely soluble in beer at cellar pressures. It only becomes a factor if you push carbonated beer with pure nitrogen at high pressure for long periods, which can shift carbonation. Use CO2 or a blend for that.

If you brew and you are still paying to have every cubic foot of inert gas trucked in, a nitrogen generator for breweries is one of the few pieces of equipment that pays for itself and also takes a supplier off your critical path. Size the compressor with it, treat the air, and put a receiver on the outlet.