Can You Stop Boiling Sap and Start Again
The following article covers some of the most common frequently asked questions regarding the procedure and methods for collecting and boiling maple sap for the purposes of making maple syrup for the home hobbyist.
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For detailed instructions on how to tap maple trees, boil maple sap, and perform the maple syrup finishing boil, check out these articles:
Making Maple Syrup – Part 1 – How to Tap Maple Trees for Sap
Making Maple Syrup – Part 2 – How to Boil Maple Sap
Making Maple Syrup – Part 3 – How to Perfect the Finishing Boil
FAQs on Boiling Maple Sap for Syrup
The principle of boiling down your sap into maple syrup is really easy. You basically want to boil off the water, so that you are left with the highly concentrated sugar-water (syrup).
What is an Evaporator for Maple Syrup?
You may hear the term 'evaporator.' This is nothing more than a boiler consisting of a heat source to make the sap boil and a pot or pan to hold the sap. Part of the fun for many maple syrup hobbyists is inventing and building their own evaporator and improving its design every season!
A simple and efficient method to get started is using an outdoor propane boiler (commonly called a 'turkey fryer').
How long does it take to boil Maple Sap into Syrup?
It takes about 1 hour per gallon to evaporate maple sap into syrup. For example, it would take 10 hours of boiling to reduce 10 gallons of sap down to 40 oz of maple syrup.
How much Maple Syrup can you get from 5 gallons of Sap?
A typical ratio for sugar maple sap to syrup is 32:1. So if you start out with 5 gallons of sap, you will end up with 20 oz of Maple syrup. To get 1 gallon of maple syrup, you would need to start with 32 gallons of sap.
Typical ratios of sap to syrup run anywhere from 20:1 to 40:1, depending on the sugar content of your sap.
Sugar maple trees tend to have the highest sugar content, so often the ratio of sap to syrup for a sugar maple is on the order of 32:1 or so, at least in my experience. If you don't mind 'watery' syrup, then you can get away with less boiling, so you end up with a higher yield, like 20:1.
| Type of Maple Tree | Sugar Conc. of Sap (%) | Ratio of Sap/Syrup |
|---|---|---|
| Sugar Maple | 4.5 | 19:1 |
| Red Maple | 4.1 | 21:1 |
| Amur Maple | 3.9 | 22:1 |
| Silver Maple | 3.4 | 26:1 |
| Box Elder | 2.5 | 35:1 |
What is the Sugar Content of Maple Syrup?
The sugar content of maple syrup is 66% by mass, and 87% by volume.
How do you Calculate the Sugar Content of Maple Sap From the Ratio of Sap to Syrup?
There seems to be a lot of confusion regarding how the ratio of sap-to-syrup can be used to determine the sugar content of your sap.
The confusion comes from the fact that Brix is a percentage of mass-to-mass, whereas Sugar Content is a percentage of mass-to-volume. Syrup at 66°Brix has 66 grams of sucrose in a 100 gram sample of syrup, but it has 87 grams of sucrose in 100 mL of syrup.
For small amounts of sugar in a solution (like sap), the Brix and Sugar Content are nearly the same. However, as the concentration of sugar increases, the Brix value and the Sugar Content values begin to diverge (see the graph below).
This table shows the Brix value and the corresponding Sugar Content % for lower Brix values (typical of sap, e.g., 3°Br)) as well as higher values (typical of syrup, e.g., 66°Br) (equation from wikipedia, sg values from Table 109, NBS Circular 440):
| Brix | Grams of Sucrose per 100 mL of Syrup |
|---|---|
| 0 | 0.0 |
| 1 | 1.0 |
| 2 | 2.0 |
| 3 | 3.0 |
| 4 | 4.1 |
| 5 | 5.1 |
| 10 | 10.4 |
| 15 | 15.9 |
| 40 | 47.1 |
| 60 | 77.2 |
| 64 | 83.9 |
| 65 | 85.6 |
| 66 | 87.3 |
| 67 | 89.0 |
| 68 | 90.8 |
| 69 | 92.6 |
Note that the sugar content by volume is about 87 for a Brix value of 66.
There is a simple equation that is used for this is sometimes called "Jones Rule of 86," named after C. H. Jones, a researcher at the University of Vermont who published a paper with J. L. Bradlee in 1933 called "The Carbohydrate Contents of the Maple Tree." The details of which were made clear to me in an old publication called the Maple Sirup Producers Manual (Willits and Hills, 1938) on page 48.
By the way, the "Rule of 86" applied back when the standard Brix value of Maple syrup was 65.5°Brix. Now that standard maple syrup is 66°Brix (66.9°Brix in some states), the value should now be the "Rule of 87."
For sap, the percent of sugar (weight to volume) is small (typically 1-5%), so Brix and Percent of Sugar-to-Volume are nearly the same. Standard density maple syrup has a Brix value of 66°Brix, which corresponds to 87.2% solids as sugar.
The following table shows how many gallons of sap are required to make 1 gallon of syrup for various sap sugar concentrations.
| Sap Sugar Conc (%) | Ratio | Gallons of Sap to Make 1 Gallon of Syrup |
|---|---|---|
| 0.0 | – | – |
| 0.5 | 174:1 | 174 |
| 1.0 | 87:1 | 87 |
| 1.5 | 58:1 | 58 |
| 2.0 | 44:1 | 44 |
| 2.5 | 35:1 | 35 |
| 3.0 | 29:1 | 29 |
| 3.5 | 25:1 | 25 |
| 4.0 | 22:1 | 22 |
| 4.5 | 19:1 | 19 |
| 5.0 | 17:1 | 17 |
| 5.5 | 16:1 | 16 |
How much does it cost to make Maple syrup?
Buying all the supplies to make Maple syrup for home use will have a one-time cost of about $200. After that the cost of propane will come to about $25 per gallon of Maple syrup (assumptions: sugar content of the sap is 3% and the price of propane is $2.79/gallon). If you chop your own wood and boil maple syrup over a wood fire, then it is "free."
The average price per gallon of Maple syrup in the U.S. varies from year to year. It reached a peak of over $42/gallon in 2008 (Ref. Table 1, p37). In 2019, the average price was $31/gallon (ref.).
The bottom line is that if you are making maple syrup to save money, try something else. The main benefit of making your own maple syrup comes from the fun and satisfaction of taking sap from a tree and making something beautiful and delicious out of it.
How do I know when Maple syrup is done boiling?
Maple sap has finished boiling into Maple syrup once the temperature has reached 7ºF above the boiling point of water. In most places this is around 219ºF. For higher accuracy, use a hydrometer or a refractometer and stop boiling the sap at 66% sugar content – this way you can get perfect syrup every time without the guesswork.
I wrote an article on How to Use a Refractometer for Maple Syrup in case you want more details.
Can you stop in the middle of boiling maple sap, then start up again?
Yes, since it typically requires long periods of time to boil down sap, it is quite common to boil the sap for several hours one day, then cover the sap or put it into a refrigerated environment overnight, and then continue boiling the next day.
Many maple producers continually add more sap while it is boiling for even days at a time or throughout the entire maple syrup season, and wait until all of the sap has been boiled down to perform the finishing boil just once at the very end.
One thing to note is that the final product may end up slightly darker, due to the heating and cooling process and the Maillard reaction.
My maple sap froze, should I remove the ice on the top?
Yes. Freezing maple sap is a great way to eliminate water and increase the sugar content of your sap through a process termed freeze distillation.
How does this work? When the temperature of maple sap decreases, water and sugar molecules are both moving around. Once the freezing point of pure water is reached, water ice crystals begin to form, but only once the correct structure of water molecules are in place next to each other, effectively forcing out the sugar molecules. The remaining water/sugar solution continues to increase in sugar concentration as more water freezes. The frozen part is a more pure concentration of water. A similar process is used in salt water desalination by natural freezing, particularly if repeated several times.
In practice, some of the sugar molecules get trapped between pure ice water crystals, resulting in irregular ice crystals with some sugar molecules adhering to, or trapped between, them. The result is typically not pure water ice, but rather ice with a sugar content somewhere between about 0 – 0.8% (depending on how quickly the sap froze – the slower the better).
The sugar content of pure sugar maple sap is about 3%. By removing the ice with a lower concentration of sugar, the remaining solution has an increased sugar concentration.
By repeating the process multiple times, some claim it is possible to increase the sugar concentration to above 10%. Native Americans used this technique quite effectively.
Can maple sap go bad?
Yes. Maple sap becomes cloudy when it begins to go bad. Keep the sap close to 32 deg F and boil it within 1 week of collecting it.
Should you keep a lid on the pot when boiling Maple sap?
No! The point of boiling sap is to eliminate water, by having a lid on the pot, the water condenses on the lid and drips back into the sap, repeating the process and increasing the amount of time it takes to boil sap into syrup.
How can I filter out the 'Sugar Sand' from my maple syrup?
Sugar sand, or 'niter,' are tiny condensate particulates of potassium nitrate that remain in maple syrup after all of the boiling has been completed. Sugar sand isn't bad to eat and many people just leave it in the syrup. It can be a little unsightly, however, and perhaps confuse those who are not familiar with it, such as family and friends. If you want crystal-clear maple syrup, it is best to filter the sugar sand out.
Note: "Sugar sand" doesn't actually taste like sugar (unfortunately!). In my experience, it almost seems like it has no taste at all, maybe a bit 'dusty' tasting, if anything...
The most common way to filter sugar sand from your maple syrup is to perform a 3-step filtering process while boiling the sap. The first filtering step is done with a non-woven mesh pre-filter when your sap is nearing the end of the boiling process (e.g. about 30 minutes left in boiling).
Many people filter the sap at the point where they transfer from the large-scale (often outdoor) boiling to the finishing boil (often on a stove).
The final two-steps in the filtering process are usually done at the same time and when the boiling is completely finished, by putting one or more mesh pre-filters inside of a synthetic filter. The pre-filter helps to catch any larger pieces of debris before the syrup goes through the synthetic filter.
Synthetic filters are often made from a material called 'Orlon' which is a synthetic acrylic fiber first developed by DuPont.
These have a filtering size of around 200 microns which effectively filters out the sugar sand.
Synthetic filters are normally used wet, meaning that they are soaked in hot water, then allowed to drip off before being used for filtering. If a synthetic filter is used dry, the filtering will not be as efficient, and will take much longer.
Don't rush the final filtering step! When the syrup is done boiling (around 219°F), let it cool slightly to around 180-190°F, then perform the final filtering. If you filter at a higher temperature, sugar sand can still develop, and your syrup will still look cloudy.
Can you drink Maple sap directly from the tree?
Yes! I highly recommend it, tapping your maple trees And drinking the sap makes a very refreshing drink! However, be prepared for the fact that it isn't very sweet. The sugar content is relatively low compared to something like apple juice. This is why maple sap is generally boiled down into syrup; in order to increase the sugar content.
A Few Words On Boiling with Propane
Using a propane turkey fryer is one of the easiest and efficient ways of boiling down maple syrup. Here are some details concerning what the cost and time involved.
Refill vs Exchange
The 20 lb propane tanks I use hold about 4.6 gallons of propane. I recommend that you take them somewhere to be refilled, as opposed to exchanging the cylinders – and here's why. When you exchange the cylinder, the tank you are exchanging for is not filled all the way full and typically only holds about 3.5 gallons of propane.
I usually refill the tanks at Tractor Supply, where currently the price is $2.19/gallon. So to fill one of these tanks is about $10.
How Long Does One 20 lb Tank of Propane Last?
The tank will usually burn forabout 15-20 hours total(depending on how high you turn up the heat). This is enough to boil down about 20 gallons of sap.
Additional Articles in this Series on Maple Syrup Making!
These are the links to the other articles in this series:
- Easiest Way to Boil Sap for Maple Syrup
- 5 Reasons to Use a Propane Stove for Making Maple Syrup
- How to Use a Refractometer for Maple Syrup
- How to Perfect the Finishing Boil for Maple Syrup
- What is the Maillard Reaction in Maple Syrup?
- Frequently Asked Questions Related to Maple Syrup Making
- What is the "Jones Rule of 86?" And How Can I Use it to Make Maple Syrup?
- Free Maple Syrup Jar Labels (Printable PDF)
- "How to Make Maple Syrup Podcast!"
Detailed Picture Guides on How to Make Maple Syrup at Home
For detailed instructions on how to tap maple trees, boil maple sap, and perform the maple syrup finishing boil, check out these articles:
Making Maple Syrup – Part 1 – How to Tap Maple Trees for Sap
Making Maple Syrup – Part 2 – How to Boil Maple Sap
Making Maple Syrup – Part 3 – How to Perfect the Finishing Boil
Subscribe to the "How to Make Maple Syrup Podcast!"
Listen to the "How to Make Maple Syrup Podcast!"
Or listen to past episodes right from your browser:
"How to Make Maple Syrup Podcast!"
Learn to Make Maple Syrup in 4 MINUTES on YouTube!
Source: https://practicalmechanic.com/2020/04/10/faqs-on-boiling-maple-syrup/
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