Liquid Nitrogen Dosing Tips & Best Practices

You decided to add Liquid Nitrogen Dosing to your packaging line. So, what’s next? In this article, we will share with you valuable information to guide you in successfully integrating a liquid nitrogen dosing system to your packaging process.

As a brewer or coffee roaster, you are a master of your craft. You want to share your creation beyond the borders of your pub and coffee house. This makes canning or bottling inevitable. In doing so, it may become necessary to incorporate the use of a LN2 (Liquid Nitrogen) Doser.

What is a liquid nitrogen doser? It is a vacuum insulated, open-to-atmosphere, stainless steel reservoir, mechanically designed to manage the two-phase flow of LN2, and comes with an actuator valve, controlled by a PLC to deliver a programmed and precise drop of liquid nitrogen. Sounds like a mouthful? Yes, but it is Cooler By Design TM, no pun intended.

To get you started, here are the essentials:
  1. Safety. This should be your first concern. When dealing with liquid nitrogen, you will be working with a cryogenic liquid at negative (-)320 degrees Fahrenheit which will cause frost bite on prolonged skin contact. Appropriate PPE or Personal Protective Equipment such as cryogenic gloves, safety glasses and face shield must be worn especially when setting up the system to start LN2 dosing. Once everything is all set up, and you’re not going to the touch the LN2 supply, there’s really no need to wear the cryogenic gloves as you won’t be in contact with extreme cold surfaces. However, definitely keep wearing safety glasses, not just for the LN2 doser, because it’s a smart, safe practice when operating a packaging line. Another safety concern is asphyxiation. At negative (-)320 degrees Fahrenheit, liquid nitrogen will be boiling, vaporizing to gas and expanding, which can cause asphyxiation in confined spaces. In the filling area, make sure oxygen (O2) monitors are in place and there is adequate air exchange. Provide Sub-contained Breathing Apparatus at the entrance if the filling room is a confined space. At the very least, ensure personal O2 monitors are worn by the operators. One should never compromise on safety especially with nitrogen gas as it is colorless so there is no way of visually detecting.
  2. Define what you need to achieve. What is it you are after? Your specific need defines the approach to successfully integrate LN2 dosing to your process. The following offers good advise on how best to achieve them:
    1. PRESERVATION. Shelf life extension through TPO reduction is achieved when oxygen in the head space of the can or bottle is diluted with large quantities of gas nitrogen molecules. Before we get into the details, let’s define TPO first. For TPO, the following formula applies:

      TPO = DO + HSO

      Where:

      TPO = Total Packaged Oxygen

      DO = Dissolved Oxygen

      HSO = Headspace Oxygen

      Normally, the atmosphere in the headspace of your can or bottle is Air with 78% Nitrogen, 21% Oxygen, and the balance being Argon, Carbon Dioxide, and traces of other gases. As the liquid nitrogen is introduced on the top of your container, it will immediately expand and increase the concentration of N2 gas molecules in the headspace, thereby, reducing the overall percentage of O2. Through proper LN2 dosing, the percentage of oxygen can drop to less than 1% of the headspace volume. With minimal O2 in the headspace, the rate of oxidation of the beverage will be reduced.

      Take note: Dissolved Oxygen (DO) levels are managed differently. The DO levels in beer or other beverages is a function of the volume of O2 that the beverage picks up from the brite tank, the conveyance, the pumps, and the filler. Liquid Nitrogen dosing only affects the reduction of oxygen in the headspace from the point of dosing up to the final seal at the seamer or capper. Therefore, to minimize O2 pick-up, other means would have to be taken such as inerting the brite tank, the conveyance, and the filling process with nitrogen gas among other things recommended by your filling line provider. What is the proper way of LN2 dosing to achieve headspace oxygen reduction? One must dose further upstream of the seamer or capper to allow the liquid nitrogen to boil and expand on top of the beverage. You must also guard the open container with LN2 from external elements which could blow away the N2 gas we are trying to put in. Simple flexi-glass shrouds over the conveyor, where the open container travels between the doser and seamer, helps a lot to contain the nitrogen gas molecules. Dosing further upstream basically buys you time to allow the liquid nitrogen to boil and expand. What if you don’t have the space for the dosed container to travel and allow the LN2 to boil off? This is when you use SoftDose™ Technology nozzles which facilitate the delivery of the liquid nitrogen dose in a spray pattern. This increases the surface area of the LN2 dose to accomplish quicker vaporization rates.
    2. PRESSURIZATION. With the pressure in, the cans are sturdier allowing for thinner container walls and cost savings on materials. Specifically for coffee and other non -carbonated beverages, liquid nitrogen dosing is necessary to pressurize the cans and allow it to go through the seamer. To achieve pressure in the can, there must be sufficient liquid nitrogen in the headspace prior to the final seal allowing the LN2 to boil inside a seamed can to build the pressure you need. Just be careful not to put too much liquid nitrogen to avoid over-pressuring the cans. Typically, to achieve pressure, one must dose LN2 closer to the seamer. It is essential to have consistent fill height or volume of the beverage in each can to achieve constant pressure as this defines having the consistent headspace volume. If your headspace volume varies, your final pressure for each can will also vary. Major causes of varying fill heights are mis-calibration of the fill valves and beverage splashing out of the can. Take the necessary measures to avoid and manage these causes from happening. Equally essential to achieve constant pressure when you have constant fill height is to have the same quantity of liquid nitrogen inside each can at the time of seaming. Refer to the tips listed under Preservation to keep the N2 in the can. However, you have to understand the operation of your canning line. Most inline canning systems employ the use of multiple fill valves and one seamer. For this operation, a batch of 4 to 12 cans are filled at the same time traveling all together down the conveyor towards the seamer where each can is seamed one at a time. If all of the cans have been dosed with the same volume of LN2 then each and every can in the sequence will have less and less pressure as they wait their turn to be seamed. This is because the liquid nitrogen is continuously boiling and you are losing to evaporation. A solution for this is to administer incrementally increasing dose volumes of LN2 in each can in a cycle to compensate for the wait time. The end result is to have the same quantity of liquid nitrogen inside each can at the time of seaming. Some in-line canning systems have indexing wheels or worm gears that spaces the cans apart to achieve constant time from the LN2 dose to seaming. If this is the case then you must dose the same quantity of liquid nitrogen each time. Another scenario is the rotary canning lines. One important aspect to consider are line speed changes as it affects the timing from dosing liquid nitrogen to seaming. When you dose the same quantity of LN2 each time, and the line slows down, your final can pressures will be lower. Conversely, if the line speeds up, your final can pressures will be higher. Here is where a doser with Speed Compensation ability becomes essential, commonly known as Speed Compensation feature, it adjusts the dose volume upon detection of line speed changes. This is carried out by setting up speed sensors tied in with the time of release of the liquid nitrogen dose, managed by algorithms in the doser’s PLC. For this section on Pressurization, we focused on aluminum cans. However, the same considerations also apply to aluminum bottles, PET bottles, PET cans, and other packaging types which need internal pressure from liquid nitrogen dosing.
    3. THE PERFECT POUR™ with NITROGENATION. Craft brewers like to tell their story with their product. To reach more customers they use cans, and with a can, the discerning consumer expects the perfect pour with a nice cascade and fine bubbles. Beyond the preservation, consumers also seek that perfect pour experience they get from the tap in a can. The dosing of liquid nitrogen can help, and it’s necessary for both widget and non-widget cans. Nitrogenation is what gives the consumer the same great taste and mouth appeal from a can which they traditionally get from a product poured out of the tap. How is the “perfect pour” achieved? Let’s consider a Milk Stout beer. With the can popped open, the nitrogen is released. The beer is poured and you will see the CO2 foaming action. As the bubbles rise to the top, the cascade is formed…that is a “perfect pour”! Carbon Dioxide (CO2) is part of the perfect pour, and it’s enhanced by liquid nitrogen dosing. Here is the science behind the perfect pour. With pressurized nitrogen gas in the headspace of a closed beer, the CO2 in the beer stays dissolved. The partial pressure of the nitrogen prevents the CO2 bubbles from forming. When the can is opened that nitrogen gas pressure escapes, and the CO2 can now bubble to the surface of the beer. This creates the much sought-after beer cascade or the “perfect pour”. The foamy cascade comes from the bubbling CO2 and proteins from the barley. Some of those proteins have “hydrophobicity”. This is like being allergic to water. As the CO2 bubble races for the surface, these proteins hitch a ride and bind to the bubble to avoid the water. The bubble bulks up, resulting in the cascading foam. Different proteins create different foam characteristics. Some coat the bubbles. Others make the bubbles more rigid or sticky. It all comes down to the qualities of the barley. Beer connoisseurs say a beer tastes better with a creamy cascade, partly due to the smooth texture, but also from the aromas which are pulled out of the beer as the bubbles percolate to the top. Depending on your specific objective or objectives, read further along and we will define best practices to optimize your LN2 doser.
  3. Optimize your Liquid Nitrogen Doser selection. The addition of any equipment to your canning or bottling line is a good investment to achieve a variety of new product offerings. Just like any investment, it’s in your best interest to optimize it. A good understanding of the following will help achieve this:
    • What is your market size and coverage for distribution? This defines your production output, the type of filler, and the model of LN2 dosing equipment.
    • What are the stages of your growth development? Planning for equipment set-up at start-up and upgrades as you grow will be key. Consider LN2 dosing systems that allow for upgrades to support your growth needs.
    • Should you buy or lease a liquid nitrogen doser? Evaluate the advantages and disadvantages of both. Seek providers who offer both purchase and lease-to-own opportunities.
    • Consider mobile canning services with liquid nitrogen dosing capabilities. The service exists and allows you to get into LN2 dosing rather quickly. Alternatively, this could be offering contract packaging services to others as another revenue stream.
    • Select a provider of liquid nitrogen dosing systems with actual brewing and roasting experience, and a good track record of acclaimed service support. Nothing beats a provider who knows your process.
  4. Utility Requirements. There are three basic requirements for LN2 dosers:
    • Liquid Nitrogen used for the actual dosing process, 22 to 70 psi pressure, depending on the model of doser. Typically run from a cylinder, 230 liter in capacity and obtained from your local industrial gas supplier.
    • Gas Nitrogen (GN2), used for purging the doser at start-up, and sometimes as process gas for the actuators of the doser, 60 to 70 psi pressure. Pulled from the same liquid nitrogen cylinder used for dosing.
    • Power: 110-240 VAC, 50/60 Hz, 110 W
  5. Care for your Liquid Nitrogen Doser. Now that you have your LN2 dosing system figured out, here are things to recognize and consider for long-term use and a trouble-free operation:
    • Purging: Moisture does not go well with liquid nitrogen. At negative (-)320 degrees Fahrenheit, moisture will instantly freeze in contact with LN2. Using GN2 is critical when purging. Anything other than GN2 may result in adding more moisture into the dosing system which may lead to ice formation, and ultimately blockages preventing the system from functioning properly. Purging with warm or hot GN2 is always preferable to cold GN2. Results are seen quicker as hot GN2 can vaporize moisture. Make it a standard operating procedure to always purge prior to starting up the system. NOTE: All cryogenic equipment such as the Liquid Nitrogen Doser requires purging to get rid of moisture from the environment.
    • Your liquid nitrogen doser is a double-walled vacuum insulated piece of equipment. Vacuum is pulled inside the annular space, or the space between the inner vessel and outer jacket. Do not puncture, weld or torch the outer jacket, otherwise you stand to compromise the vacuum which maintains the best insulation for LN2 to remain in its liquid state.
    • Always employ the use of a Safety Relief Valve (SRV) between two isolation valves as you can trap liquid nitrogen and have it over-pressurize the connection. Always have an SRV between the LN2 cylinder supply and the doser. The pressure rating must be in compliance with the Maximum Allowable Working Pressure (MAWP) of the doser.
    • Just like your canning line, clean the liquid nitrogen doser free of any residue of the product before and after each operation. Product residue will be the host for any bacterial growth. Being in the beverage industry, utmost cleanliness is an expectation.

We hope sharing this knowledge supports your decision to get started with liquid nitrogen dosing. Clearly, there is more to share and cover beyond this article.

Please visit our websites to download any of our educational webinars and literature: www.ChartDosers.com and/or www.DitchTheWidget.com

Until next time!!!

Juancho Tabangay
LN2 Dosing Specialist