Ohio State University Extension
This post is in response to the article on maple syrup quality written by Dr. Michael Farrell in the last edition of the Maple News. First let me say that the article was not only excellent but very timely. The article addresses an issue that all of us producing maple syrup need to look at as we start a new seasons production. What I hope to do is highlight some of the areas in the production process where quality can be compromised. These are often identified through off flavors. The University of Vermont and the Vermont Ministry of Agriculture have given us an excellent tool for identifying the sources of off flavors in maple, “The Map of Maple; Off –Flavors”. This was also published in the last edition and is also available from the IMSI publications
After producing maple syrup for over 40 years and teaching seminars on maple syrup production for close to 20 years I have made, and have seen others make, most of the common mistakes that lead to off flavors and poor quality. In this article I will go over some, but certainly not all, of the factors that lead to poor quality. Many of which can be controlled by the producers with proper best management practices. The map of Maple: Off Flavors identifies 5 primary areas where off flavors occur; Mother Nature, defoamer, processing, chemicals and others. I want to address each of these, not in order but how they would occur from the start of the season to the end.
When you start out the season you need to be aware of several problem areas that can lead to off- flavors. Most stems from equipment maintenance after the previous season and going into the new season. When producers and hobbyist ask how I should clean up my equipment, my response is with a lot of water and elbow grease. Anytime we use chemicals to clean equipment we run the risk of leaving behind residues that can compromise flavor. If we use chemicals on our pans to clean them at the end of the season the chemical residue needs to be thoroughly cleaned out. If we store filters make sure there is no mold on those filters when they come out of storage. If you have mold on your filters, throw them out. Never use detergents to clean filters it will alter the flavor. Finally make sure you store your chemicals in a secure place away from the process of making syrup to avoid unintended contamination of your product. Finally if you use a tubing cleaner make sure it is flushed from the system. If you suspect some cleaner may be left in the lines then let part of the first run go to the ground. Most of the above are common sense but they need to be mentioned.
Probably the biggest culprit when it comes to off-flavor is processing. This is where the majority of the mistakes are made that result in off flavors. When we grade syrup we look at 4 primary areas density, color, clarity, and flavor. Even though each is judged separately they are actually all interrelated. Density affects syrup quality in several ways; first syrup must be 66 brix to meet USDA standards and if it is below 66 brix it can ferment and cause an off flavor. Syrup above 67 brix normally does not have an off flavor but the higher density can cause crystallization in the bottom of the container and loss of revenue to the producer. As syrup moves across the front pan the density changes rapidly and so does the color. Density changes occur with the rapid removal of water increasing the sugar concentration. Color changes occur as the sugar molecules change due to the introduction of heat. These changes happen very quickly and need to be monitored closely. Anything that interferes with flow of sap through the evaporator can cause the syrup to get darker and possibly cause an off flavor. Many feel that density is the most critical part of the process and at times reaching the proper density can be very illusive. Improper density management can lead to two off flavors that are very common in syrup; fermented and scorched. It can also lead to an unwanted change in color. The additional boiling time can also affect flavor causing an unnatural taste that is not representative of the grade you are processing.
We use three tools to measure density, the hydrometer, the thermometer and the refractometer. All sugarmakers use a hydrometer. Hydrometers should be inspected or checked for possible problems and replaced if suspect. Often the paper with the scale printed on it can slip resulting in the wrong brix reading. The hydrometer can become coated with film resulting in an inaccurate reading. A good hydrometer will give you an accurate reading only if it is used at the right temperature. Temperatures below that require consulting a chart to get the right brix reading for a specific temperature. Maple syrup boils at 7 degrees above the boiling point of water or 219 degrees. Many producers use a thermometer to determine the draw off point. The only problem is that that the 219 reading is only accurate if the barometer is at 29.9 hg barometric pressure. A thermometer needs to be recalibrated every time the barometric pressure rise or falls. This makes a thermometers reliability somewhat suspect. However, syrup temperature is vital when it comes to setting an automatic draw off. The final tool is what many consider the judge and the jury of maple syrup density, the refractometer. What many producers do not realize is that, for a refractometer to work properly, it needs to read a product that is finished and one that is stable in temperature. This was pointed out the other day, when I had a conversation with Robert Crooks of Marcland Instruments. For a refractometer to work properly it has to be able to refract light coming through the sample it can only do that accurately if the sample in the instrument is a clear finished sample. Taking a sample of cloudy unfiltered syrup can lead to an inaccurate reading. The temperature of the product also affects the light refraction. Even though the refractometer is built to automatically compensate for temperature that temperature needs to be stable. If you leave freshly drawn off syrup set in a container it will continue to evaporate water until it cools down. Think of what happens to a roast when you pull it from the oven, it continues to cook. This is why it is recommended that you cover a container with hot unfiltered syrup to stop the loss of moisture. If you use a refractometer to set the draw off, take the syrup and run it through the filter and collect a sample allowing it to sit for 15 minutes then take your refractometer reading. This will give you the most accurate reading from your refractometer.
If you use a conventional auto draw-off, be aware that it takes time to complete the draw off process. This means that syrup will be drawn off over a range of temperatures. Therefore set the draw off to actuate slightly below the desired temperature and it will finish slightly above. Using a hydrometer is the best way to set your draw off. However, make sure you are reading the hydrometer at the recommended syrup temperature. You can use a refractometer but it has to be used on a finished temperature stable product. This process may take more time than you have to make a correction on the draw-off.
As sap moves across the evaporator temperature gradient sets up. Ninety percent of the water is removed by the time the sap reaches the middle of the front pan. Syrup needs to move from the middle of the syrup pan to the outlet relatively fast. Any interruption with this process that interferes with the temperature gradient and holds the syrup on the pan longer will result in syrup that can be darker and denser than desired. One common mistake is to allow the pans to cool during the firing process. Anytime you cool off the pans the temperature of the sap drops and this causes the boiling temperature to drop resulting in the sap on one side of the gradient to mix with sap on the other gradient. You need to keep a constant heat level on the front pan at all times. This is more critical in a wood fired evaporator.
The other problem is foam control. Excessive foam in the back pan can cause problems with you float and may interfere will your ability to control the level of the sap in the evaporator. If this happens you will need to use a defoamer to control the problem. When using defoamer, the only place the defoamer should be added is at the point where sap enters the rear pan and occasionally a couple of drops if needed, at the draw-off if foam builds up as you are drawing off. This should be done at regular intervals placing the prescribed number of drops (2 drop per foot of width) where the sap enters the evaporator. Never spray defoamer across the front pan to control foam. Using defoamer in this manner will impede the boil and break down the gradient. This can lead to the dreaded big batch. If the front pan is foaming excessively, then the foam is not being properly controlled in the back pan, correct the problem back there. Use only small amounts of defoamer, excessive use can result in an off flavor. Organic producers must use safflower or canola oils which are very poor defoamers. Be careful, using an excessive amount of these products can result in an off flavor.
The other problem that can cause scorching in an evaporator is to allow niter to buildup. When niter buildup it will insulates the bottom of the pan from the liquid creating a potential hot spot which can result in a scorched spot on the pan. You need to keep liquid in contact with the pan at all times. Always keep your pans as niter free as possible by rotating sides or using a clean set of pans. Using a good syrup filtering system to remove niter is vital if you want to produce syrup that meets the clarity standard. You should be able to read newspaper print through a sample bottle of syrup that has been properly filtered. Cloudy syrup with a lot of niter can produce an off-flavor. Remember every time you heat your syrup to a boil more niter will precipitate out and it will need to be re-filtered. That is why you do not want to bring your syrup to a boil when canning. 185 degrees Fahrenheit is the required temperature for canning.
As maple producers we fight the growth of bacteria through our entire system. When bacteria colonies multiply within sap they convert sucrose sugar molecules to Glucose and other invert sugar molecules. This increase in invert sugar, when exposed to heat will cause a darker product. This is most prevalent at the end of the season when the bacterial content of sap is at its highest. Bacteria can affect the entire process of making syrup from the tubing system right through canning. Because sap has a sugar content it is a perfect media for bacterial growth. It goes without saying you can never be too clean when it comes to making syrup. Sap needs to be collected in clean equipment, it need to be kept cool and processed quickly. At the beginning of the season if we start with a properly sanitized system we have few problems with bacteria but as the season progresses the problems increase. Maple Producers need to know when to end the season. Producing syrup late in the season when the trees are near budding and the sap is out of condition has little value to you or the industry. Syrup also needs to be packaged correctly to control bacterial growth in container that can lead to spoilage. That is why we always pack plastic jugs at 185 degrees. This prevents condensation which can supply an environment for bacterial growth in the container.
As you can see there are many areas within the process of making syrup the sugarmaker can have an impact on the quality of the product that is producing. The is attention to detail from equipment sanitation to efficiency of processing is what separates many producers when it comes to product quality. Making the highest quality product possible should be your goal, you reputation as a maple producer depends on it.