reverse osmosis takes the water out of maple sap to turn it into the delicious maple syrup we all want to eat

Curious George learned the lesson the hard way: when the maple sap comes out of the tree, it tastes pretty much like water. It takes 40 or more gallons of maple sap to make one gallon of maple syrup. As George found out, the raw sap on pancakes does not taste good. The sap must be concentrated, and that means removing a lot of water.

The traditional method to concentrate sap into maple syrup has been to boil, boil, boil.  This is why you see the steam billowing from the cupolas of the sugarhouses all day long in the spring. However, in today’s modern sugarhouses, much of the water content of the sap is removed by using something called reverse osmosis. This process removes much of the water before it’s ever boiled. By starting with a higher concentration of sugars, the boiling time is greatly reduced. So what is this thing called reverse osmosis?

Reverse Osmosis: a process by which a solvent passes through a porous membrane in the direction opposite to that for natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure

Basically, powerful pumps force the maple sap through porous membranes. The water is squeezed out, but the sugars are too big to fit through the membrane. They are left behind in a more concentrated form. It’s that concentrate that is then boiled to make the finished maple syrup.

The use of reverse osmosis (RO) in the maple industry these days is extremely common. The technology is used to make almost every bottle of syrup that most people will ever taste. Due to its prevalence, I believe that people should know what it is and what some of the pros and cons are. I personally do not use reverse osmosis when making my maple syrup. Maybe someday I will, but for now there many reasons that I don’t. Regardless of my preference, the technology definitely has a place in the maple industry.

A Look at the Numbers

The RO process can be used to concentrate the sap to various sugar levels depending on the equipment used. The sugar content of the sap is measured in degrees Brix (°Bx), which essentially represents the percent sugar content in the maple syrup. Raw sap straight from the tree is about 2% sugar. That’s like pure water but with just a hint of maple. Maple syrup, the thickened sweet stuff that we like to pour on our pancakes, is about 67% sugar.

The impact of the reverse osmosis technology on the maple production process can be extreme. Small reverse osmosis systems might bring the sugar level from 2% up to 4%. That doesn’t sound like much, but the concentrate is twice as sweet as the raw sap. With 4% concentrate, the boiling time would be cut in half. An eight hour day would be cut down to four hours. Or perhaps you could double the number of taps without impacting your boiling time. All of a sudden, the lure of RO becomes readily apparent.

Imagine you are using one of the latest high-Brix systems that can bring the sap to an incredible 32% sugar content. That’s about half way to the sweetness of syrup, and nothing’s even been boiled yet. Looking at some rough numbers: 4% concentrate cuts time in half; 8% cuts in half again; 16% cuts in half again; 32% cuts in half again. Now your eight hour day is cut down to a half hour. Talk about a time saver! It wouldn’t make sense to fire up an evaporator for half an hour, but increasing your number of taps 16 times over might. The latest reverse osmosis systems are now getting up to a whopping 45% sugar content. That’s closer to syrup than water. You can see how operations quickly size up to take advantage of the technology.

I visited a sugarmaker who had an impressive operation on top of a mountain. I’m not sure what percent his RO system could handle, but he said that after he flipped on the oil burner, he could produce a barrel an hour. That’s a lot of maple syrup. However, in today’s maple industry, that farmer is nowhere near the size of the biggest producers. In an article from 2019, The Maple Guild, AKA The Island Pond Maple Factory, AKA Sap Jack, stated they could make a gallon of syrup every 1.6 seconds. Wow. Factory farms have certainly made it to the hills and woods of Vermont.

Environmental Impact of Reverse Osmosis

With that much syrup production, there’s also a lot of effluent, or ‘waste’ water discharged. With about 40 times as much water as syrup, the Factory in northern Vermont would discharge about 4,000 gallons of effluent for every minute when they are in production. I will admit that I have no idea how they handle it and I’ve never visited the factory. I’m only putting the pieces together and conjecturing. I do know that there have been discussions about possible regulations in the works to address the water discharge. I’ve also heard about a company in NY that plans to bottle effluent and market it as ‘tree water’. Really?!

The electric power required to run these RO systems is enormous. Most smaller farmers need to run additional power to their operations when they install the equipment. The trade off is that they save time and they don’t need to burn as much in their evaporators. Much of the electric power in the Northeast is derived from hydro-electric dams. They have their pluses and minuses, but there is an argument that reverse osmosis is better for the environment. That seems especially true for sugaring operations that burn fuel oil. The State of Vermont even offers incentive programs for maple farmers to add reverse osmosis systems.

An incentive program might be required for small maple farmers to even consider adding an RO system to their farm. When I was starting up my sugaring operation, I asked for a quote for a reverse osmosis system that could handle sap from about 2,500 trees. The estimate was $20,000. That didn’t include running the electricity, insulating the equipment room, all the required fittings, or ongoing maintenance. When faced with that sort of capital investment, it’s understandable that many small farmers would prefer to keep it simple, and just spend the extra time and firewood like their predecessors did. There’s beauty in the tradition.

Impact to Maple Flavor

Those are some of the nuts and bolts of RO, but what about the impact on flavor? UVM conducted a study back in 2010 that looked at the impact to flavor of maple syrup that was concentrated to 8% sugar with an RO system. The result was that the flavor difference were essentially undetectable. But there's more to the story. The RO technology has advanced dramatically in the last decade and most producers concentrate to well above 8% sugar content.

A fellow sugarmaker was at an equipment dealership a few years back and the sales rep was pitching reverse osmosis systems to a group of sugar makers. He warned them not to jump into reverse osmosis with a 20% RO machine right from the start. He suggested that they start with a rather low concentration percentage and then slowly increase the concentration levels over a few year period. That begged the question of why, especially since the increased production numbers were so alluring. The response: you’ll lose all of your customers because the flavor is so different.

I’ve only tasted ‘high-Brix’ maple syrup once. My first impression was that it tasted processed. Sure, it was maple flavored, but it just had a refined sort of essence to it. It was not served side-by-side with other syrups so it was hard to do a fair taste test. The sales rep from the equipment company was prancing around the room with the tray of samples telling the sugar makers how good it was while smiling and nodding. Just slightly biased.

I’d like to see the same group of maple producers sit down to a blind taste test with high-brix vs. no reverse osmosis syrup. I seriously doubt that the highly processed maple syrup would be the winner. I’ve heard it myself over and over again from farmers who don’t use reverse osmosis: customers and those in the business all say the syrup flavor of traditionally made maple syrup is better than when high-brix reverse osmosis is used. 

Personal preferences are certainly subjective. While I prefer the more traditional caramelized flavor of what I consider real maple syrup, others will prefer a lighter, more refined flavor. Some even prefer 'table syrup' made with no maple at all. That is something I'll never quite understand.

Maple Farmers and Reverse Osmosis

As of today, only a couple of the farmers working with Maple Farmers are using reverse osmosis. That isn’t to imply I don’t want to work with folks that use the technology. I want to work with small farmers, and a lot of them simply can’t afford to get over the capital investment hurdle. When I do start working with farms that use reverse osmosis, I pledge to only work with those that don’t go ‘too far’ with the concentration process. Our products are all about the flavor, and that is not something I’m willing to compromise by moving to high-brix maple syrup. I hope you try some of our syrup, and if you get a chance, try some side by side with some run-of-the-mill maple syrup from the grocery store. You’ll taste the difference.