Small-Scale RO Maple Syrup Production for the Hobbyist
By Gary Battenberg
A brief history
Maple syrup production is not only a popular hobby for those who want the authentic product for their flapjacks but it is becoming a small-business venture for many home-based producers all over the country. When local farmers’ markets open in early spring, it is common to find pure maple syrup on display, available for sale in small bottles and in some cases, even in gallon jugs.
When you think of maple syrup, does the image of a log cabin with smoke rising from the chimney come to mind? Perhaps a wagon-load of maple sap pulled by a team of horses to the sugar house where the sap is heated to evaporate the water? Or, how about a maple tree with buckets hooked on to collect the sap? Log Cabin and Aunt Jemima table products have been around for many years and taste good. They are not real maple syrup but rather are maple-flavored and made with sugar. To avoid false advertising claims, the wording is carefully crafted as ‘Authentic Maple Tasting Syrup’ and a closer look at the ingredients reveals these products are made with corn syrup.
In the 17th century, some dairy farmers would supplement their regular milk income during the short weather window between late winter and early spring, making and selling maple syrup. This work took place when daytime temperatures were around 40°F (4.44°C), following overnight temperatures below freezing. Maple syrup production in the early days was very labor intensive. Small holes were drilled into the tree and small tubes (taps) inserted that would allow the sap to be collected in buckets. They were carried to a central location (usually in the nearby woods) where the water would be boiled off in evaporators, which were (essentially) huge frying pans with fire boxes built underneath to yield the concentrated sugar for syrup production.
Shortly after the turn of the 20th century, St. Johnsbury, VT was the Maple Capital of the World. George C. Cary founded the Cary Maple Sugar Company, which controlled as much as 80 percent of the bulk maple sugar market of the period. His success was due (in large part) to reducing the manual labor associated with maple syrup production by modernization of sap collection, transport, processing, packaging and marketing.
Collecting the sap
Sap is approximately 98 percent water and it requires between 40 and 50 gallons (151.4 and 189.2 liters) of sap to make one gallon of maple syrup. Sap flows during a freeze, thaw and flow cycle. When the daytime temperature rises above a certain point, positive pressure develops in the tree, which causes the sap to flow out of an opening in the tree bark. The sap is replenished when the temperature drops again, creating suction, which allows the tree to uptake water to replace the lost sap. It is important to know that the sap is to be collected before the buds appear on the tree; otherwise, the sap acquires an undesirable tart taste and is not suitable for production.
How many taps and how much sap?
Taps are simply small holes (0.375 to 0.5-inch/9.5 to 12.7mm diameter) drilled at a slight upward angle and about 2.5 inches (6.35 cm) into the tree to reach the sapwood. To determine the number of taps a tree can support depends on the diameter of the tree. The tree diameter should be measured between four to five feet (1.2 to 1.5 meters) up from the base. A tree with a diameter between 10 to 17 inches (2.54 to 4.31 cm) will support one tap. Trees measuring between 18 to 24 inches (4.57 to 6.09 cm) will support two taps and diameters greater than 25 to 30 inches (6.35 to 7.62 cm) will support three taps. These recommendations ensure that not too much sap is extracted in order to maintain the health of the tree. Approximately 15 gallons (56.7 liters) of sap from each tap per season is the maximum recommended collection volume.
Three methods of collecting sap are used, including hooks and buckets, gravity lines and vacuum lines. For the hobbyist, the original hook and bucket method is the most simplistic and cost-effective (albeit more time-consuming) because the buckets must be manually carried from the tree to the storage tank. For those who have a small home-based business, the gravity and vacuum systems reduce the amount of manual labor attributed to the original method and the cost may be justified based on the seasonal volume.
The gravity system connects the taps from several trees to a gravity line that empties into a central storage tank. This method requires more thought and planning because the storage tank must be at the lowest point on the piping system and requires a large land area. The vacuum system is set up the same way as the gravity system but includes a vacuum pump, which draws the sap from the trees in a shorter time, which in turn leads to a higher sap yield.
Storage of the sap in preparation for de-watering is a critical phase for the hobbyist because this is the most difficult part of the collection process. Sap will spoil in the same way as milk, which means it must be kept chilled to prevent build-up of yeast and bacteria before the sap is processed into syrup. This build-up will have a negative impact not only on the taste of the syrup but also on premature filter plugging in the processing system. To prevent this from happening, processing the sap should not exceed seven days from collection. For larger hobby operations, where bulk quantities of sap are collected before production, sap can be pretreated with UV light to destroy harmful yeast and bacteria.
Boil or separate?
After collection and storage, the next step is to remove the water from the sap. (Traditionally, boiling the sap to evaporate off the water until the sugar concentration reaches the desired level, as measured by a refractometer, was the practical method for many years.) The boiling process involves pouring the sap into a large pan above an oven called an arch. The arch provides the heat for the pan which is specifically designed to allow the sap to flow and boil evenly. The disadvantage for the hobbyist is that the energy cost to boil off the water is prohibitive, especially for the small-batch hobbyist. There are several different fuels available for heating the arch, including fuel oil, natural gas, kerosene, wood and propane, all of which are costly. When energy costs are added to the equipment and material cost, a more economical approach is desirable and would be ideal. Fortunately, a more efficient way to remove the water from sap can be accomplished with membrane separation.
Separation by reverse osmosis
Up to two-thirds of the water in maple sap can be separated by using reverse osmosis before the boiling process, which will reduce the boiling time and relative energy costs. Operating the RO system at 120 to 200 psi applied membrane pressure will efficiently reduce the sap to a consistency suitable for boiling. Maple sap sugar will range between one and four percent, with two percent being the average. At two percent, you can separate up to 75 percent of the water with an average product-to-waste recovery ratio of 1:10 to 1:12.
Basic component list
For small-batch processes (one gallon/3.7 liters), a clean work environment and food-grade components are needed as follows:
• 55 to 60 gallon (208.1 to 227.1 liter) bulk batch tank
• Transfer pump
• Dual gradient prefilter package with differential gauges
• 1,500 gpd RO system with pressure gauges, permeate, concentrate and recycle flow meters
• Optional immersion heater
• Treated sap tank
• Treated sap recirculation pump
• Permeate tank
• Metering needle valves, SS
• Check valves
• Half-inch tubing and fittings or piping materials and service/isolation/cleaning valves
• Glass bottles for packaging the syrup
• Custom product labels
The complexity of a system is only limited by one’s knowledge of RO operation and maintenance, as well as understanding the nuances of assembling and operating a complete system properly sized for the estimated production volume.
When syrup production is complete for the season, it is important to thoroughly clean the system by flushing with clean water and sanitize with hydrogen peroxide solution. Prepare the RO membrane for storage with a membrane preservative recommended by your RO system supplier. It is not advisable to remove the membrane from the vessel to store in the off season. Once the RO system is completely cleaned and drained, it can be stored in a cool location (but don’t allow the system to freeze). There are some good suppliers that provide excellent technical support for the hobbyist, whether it is a small system for personal use or a larger system for the small enterprise. The Internet is a good place to search for the right combination for the project. You may also want to speak with your RO equipment supplier and inquire of their experience with maple sap separation. RO has been used in maple syrup production for more than 40 years and is a viable alternative to reducing the water content versus the traditional boiling/evaporation method.
Maple syrup production for the hobbyist is a growing trend; perhaps you may wish to join the crowd in this emerging market. With natural food of all kinds being highly sought after in farmers’ markets and select organic grocers, perhaps this may be a seasonal activity that fits with your enterprising spirit. If not, you can certainly take pride in enjoying your homemade, 100-percent pure maple syrup on your flapjacks, waffles or French toast.
About the author
Gary Battenberg is a Technical Support and Systems Design Specialist with the Fluid System Connectors Division of Parker Hannifin Corporation in Otsego, MI. He has 36 years of experience in the fields of domestic, commercial, industrial, high-purity and sterile water treatment processes. Battenberg has worked in the areas of sales, service, design and manufacturing of water treatment systems and processes utilizing filtration, ion exchange, UV sterilization, reverse osmosis and ozone technologies. He may be reached by phone at (269) 692-6632 or by email, email@example.com