Down the Vacuum Sealing Rabbit Hole
Computational chemist Chris Hendon and a few smart coffee people got together and tested how various coffees behaved when ground at various temperatures below freezing. I recommend reading about it here and here. My rough summary of what they found is that the lower temperature coffee is when it’s ground, the “better” the distribution of particle sizes (ie. grind quality). With higher grind quality comes the ability to extract more evenly the coffee, and a better-tasting cup results. Another benefit to storing coffee at freezing is that freshness is preserved for a really long time.
For a cafe, however, the logistical challenges outweigh many of the benefits. Vacuum sealing doses of coffee requires lots of time and even more plastic. Coffee doses cannot simply be frozen, as the moisture and oxygen will have detrimental impact on the coffee. Moreover, the methods recommended by Michael Cameron here are a good starting point, but difficult to pull off in a cafe. In order to offer customers fresher and tastier coffee, we’ve invested time into finding a method for vacuum sealing that addresses concerns of sustainability and efficiency. In this article I will provide an overview of the vacuum sealing methods we tried, why we tried them, why they failed, and what method ended up working for us.
The FoodSaver
Our initial setup was fairly simple: a small under-counter freezer, a FoodSaver vacuum sealer, a paper trimmer, and an impulse bag sealer. This setup was based on Micheal Cameron’s aforementioned article. To summarize: we would use the paper trimmer to cut down to size rolls of vacuum sealing bags. Our bags were around 3" x 5" and were sealed by the impulse sealer on all but one side. Coffee would be weighed out in a container and dosed into the open end of the 3"x5" bag. With the FoodSaver, we were able to seal one to three bags at a time. The vacuum sealer took about 15 seconds to complete its sealing process. After that, each bag would be labeled according to its brew method (F for filter, E for espresso), the initials of its origin and name, and the roast date. Coffees would then be stored by method and coffee type and placed into the freezer.
The above method allowed us to taste through coffees and track their performance/reception while they were vacuum sealed and frozen. However, for a café the method has many shortcomings. Between cutting the bags, sealing them, dosing, vacuum sealing, and labeling the process took a substantial amount of time and active attention from staff. Equally problematic was the amount of waste this method produced. Waste was created in two ways. First, despite cutting bags to their smallest functional size, we generated a lot of plastic. The bags were single-use and brewing hundreds of coffees per week would have led to irresponsible amounts of waste. Second, we experienced a high failure rate of the bags we made (around 10% of the bags failed to hold a seal). Any imperfection in the seal created by the impulse sealer or FoodSaver would lead to a break in the seal. The rigidity and sometimes low quality of the plastic made achieving perfect seals consistently difficult. This wasted extra effort, coffee, and plastic. Convinced of the value of vacuum sealing and freezing doses but uninterested in such a wasteful method, we started looking for a more sustainable and efficient method.
Nails, Electrical Tape, and Jars
Our next idea was largely informed by canning forums. We started looking for ways to seal coffee in small jars. FoodSaver makes sealable lids for Mason Jars but those were much too large for doses ranging from 15g to 21g.
We ordered a bunch of 2oz jars with metal plastisol-lined lids (more on that soon). Our sealing method was based on this method. We used a small nail and hammer to puncture holes in the center of each lid. The hole we then covered with a small piece of electrical tape. Our process for sealing is as follows. We’d weigh our doses in the glass jars and tighten the jar lid.
The electrical tape would be placed or adjusted on the lid so that it was just lightly covering the hole. We were able to create a seal by holding the accessory attachment on the FoodSaver against the jar lid. Because the tape was on loosely, air could be pulled out of the jar.When the FoodSaver completed its vacuuming process, the sudden increase back to atmospheric pressure forced the tape down, creating a seal. Because of this phenomenon, we were able to stop the FoodSaver mid-seal (once it had fully sealed, but not released) and achieve the same seal quality. This increased the rate at which we could seal batches of coffee by a modest amount.
The jar method worked well in that the jars were relatively easy to seal, generated no plastic waste, and were much easier to store than the bags. Not needing to cut and seal bags helped shave time off the process. Unfortunately, only being able to seal one coffee at a time may have offset the gains.
Chamber Sealers, Canning Forums
Improving the output rate was the next focus of ours. The goal was to find a way to seal as many jars at a time as we could. We tried sealing multiple jars at once in a FoodSaver container. However, the strength of the pump and design of the container didn’t work. A food-grade chamber sealer might have worked but they’re cost-prohibitive. Eventually, we discovered vacuum chambers designed for degassing compounds and “materials”. Here is an example of one.
The chamber sealer is simple. It’s just a pump that connects with hoses to a lid that seals against a container. When the lid is placed on the container and the pump is activated and vacuum valve opened, air is pulled out of the container until the pressure reaches -30psi/-1bar. Next, the vacuum valve is closed and the pump is shut off. There is a second valve that opens the lid and allows the container to return to atmospheric pressure. To make sealing jars work, we kept the tape pressed firmly attached to the lid. Lids were screwed on lightly so that air could be pulled out. The container can hold and seal up to 17 jars. After the vacuum is created, the force of air being let back into the chamber presses the jars down. The plastisol liner of the lid would seal against the rim of the jar. Jars had to be checked for seal and, if sealed, be tightened. We can identify the jars that are sealed because the lids have a stronger resistance to being turned. To make sure the seal stayed, we’d tighten the lids as much as possible. Using a chalk marker, we’d mark the lid with an assigned color or symbol. Jars would then be stored in a freezer.
It was when jars had sat a while in the freezer that we noticed sealing defects. Occasionally, and without much predictability, the jars would lose their seal. The problem was that the Plastisol lining the jar lids becomes solid at freezing. That brittleness makes for a seal that is really fragile and prone to randomly breaking. Coffee doses that had lost their seal would see a decrease in quality, especially when frozen for longer than a couple of days.
In canning, the jar lid/plastisol liner is heated to a temperature at which it is more malleable and can create a longer-lasting seal. We did not test ways of heating the lids prior to sealing because 1) in a heated sealing method, plastisol is single-use and 2) we did not want heat to affect coffee quality. Our next step was to find a material that would not lose its seal-holding capacity at low temperatures and that was food safe.
Liners, Liners, Liners
We started researching materials that would work and discovered a wide variety of jar lids and liners. There are many liners out there that can handle temperatures as low as -80F. The problem is that the material is so hard that a seal can’t be created in our setup. Vinyl-lined lids, for example, didn’t work well because they lacked the flexibility to be pushed against the rim of the jar and hold the seal. There were no jar and liner combinations that would work for our purpose.
Our next attempt was to find a silicone that could be applied to unlined jar lids. We experimented with a tube of Red RTV silicone (see this spec sheet for info). Our plan was to dispense the silicone into syringes and apply amounts around the inside of the jar lid–the way the plastisol liner had been applied. After a few applications of the silicone, it became obvious that this approach would not work. It’s challenging to evenly apply the silicone around the jar, even with a syringe. Air in the syringes would cause the silicone to shoot out unevenly and couldn’t be fixed by smoothing it out with a flat tool or finger as we had hoped. Once cured, the rough finish of the silicone prevented jars from sealing well.
Finally, we looked for gasket manufacturers who could cast or cut silicone to our specifications. There are plenty of companies local to us that handle cutting materials or gasket manufacturing. They also stock FDA-approved gasket material with the properties needed for sealing and freezing. Instead of a gasket or liner, we opted to use a solid disc-shaped piece of silicone. Using a solid piece of silicone, we wouldn’t have to worry about attaching the seal to the jar lid. The disc itself is what maintains the seal–the lid functions to hold the seal in place.
The silicone disks we use have a thickness of 1/16", durometer of 60A (this is a measure of the hardness of the plastic, higher durometer ratings mean a harder material, harder materials are less likely to seal in our system), and a diameter of 52mm. The material handles temperatures as low as -100F. That’s good news for us if we find feasible ways to store coffee at even lower temperatures.
Current System
What we hope is our final setup for vacuum sealing is this. We use unlined plastic jar lids, the silicone discs, and glass jars.
Coffee is dosed into jars (we love Acaia’s Auto-Tare feature very much). The liners are placed in the lid (or are checked to be in place), and the lid is loosely tightened against the jar. After vacuum sealing, the jars have a noticeable indent. We have yet to encounter a jar that, after being sealed, has lost its seal.
Miscellaneous Stuff
- Jars are labeled with a color and/or symbol. That allows us to quickly retrieve the correct dose while on bar. Filter coffee doses are just a line of a given color, espresso doses are a bracket-like shape.
- We use Notion to store all of our recipes and information on coffees, including their assigned color.
- When we are dialing in a coffee, we’ll dose/seal/freeze a good amount more than what we expect to use (22g or so) so that we can adjust our dose easily.
- We seal our coffees in batches in mason jars on the same day we seal the dial-in amounts. This is to keep the coffee at the same freshness as our dial-in doses. Mason jar liners are also made of plastisol, so you’ll need an alternative lid and liner like these. Mason jar lids get labeled with coffee information in their assigned color and are stored in black totes to keep them in the dark.
- Once a coffee has been dialed in, the mason jars are opened and coffees are dosed out.
Finding the best materials and processes for vacuum sealing took a lot of time and research. It’s our hope that this article can help expedite that process for cafes exploring vacuum sealing.
