Holding concentrate in a working bulk tank

[emericksmaple]

We are looking at installing a working bulk tank for next season. We will be concentrating to 15% - 16%. Does anyone know how cold we can go at that brix, before it will feeeze? I know the places that do high concentrate can go into the upper 20's.

[maple flats]

Check with Dr Tim, he gave that answer or formula before.

[DrTimPerkins]

Here you go. Approach the setpoint slowly. Thermometers and refrigeration can vary by a few degrees. Lower the temperature gradually. If slush starts to form, back off a little. An ice-cube in your bulk tank can ruin your day (or three).

22278

[emericksmaple]

Thank you, Dr. Perkins

[upsmapleman]

My question is do you need to take it down to just above freezing or can you take it to say 35 degrees and hold it.

[DrTimPerkins]

You can do whatever you like, but the colder you can keep it the longer it will store.

[Bucket Head]

Dr. Tim,

Any suggestions on what temperature any given percentage of concentrate should be stored at? Did you experiment any with different percentages and temps. when you got your tank? A lot of RO's out there with different performance levels so there might be a "no hotter than" temperature folks could aim for with their refrigeration set ups.

Thanks.

Steve

[DrTimPerkins]

Hey Steve ... Not sure exactly what you're looking for, but sap/concentrate spoilage is a function of time, temperature, sugar concentration and initial microbial load. We have done studies on it, with the following general results:

- warm sap spoils faster than cold sap
- higher sap sugar spoils faster than lower sap sugar
- sap spoils more the longer it is left out
- if sap has a lot of microbes to start with, spoilage will be faster

The colder it is kept, the longer it will last, but there is no single setpoint that we can say after this it is bad. Somewhat depends upon the types of microbes in the sap and aeration to some degree as well. Best way is to think of it as milk....how long would you leave it out at a given temperature and still drink it? An hour at room temp...probably OK. A day at room temp....probably not.

The issue this week is likely to be sap souring in the lines even before it reaches the sugarhouse. We are going to segregate our sap into different tanks and do test boils to see how it is....if it gets bad, we'll dump it until after a good freeze and hope that a return to cold weather will flush out the lines.

[Shaun]

"Somewhat depends upon the types of microbes in the sap and aeration to some degree as well. "

Is aeration a good thing or bad thing? Does UVM run the agitator in the tank continuous, some or not at all?

[Bucket Head]

Dr. Tim,

I had not seen the chart you provided before with the freezing points of concentration. So I was wondering if there was a "not good enough" temp. for concentrates. Or put another way, for instance, 8-10% sap could be held safely at average refrigerator temps. but high concentration has to be held at far below 32 degrees. And that got me to thinking about my set up.
For the record and for comparison, I hold 10-12% concentrate at 34 degrees, which is the lowest setting on my tank. Not sure how or if I could get it to go lower, but I have had great results with this tank at these levels.

Steve

[DrTimPerkins]

Does UVM run the agitator in the tank continuous, some or not at all?

We run the agitator if there is concentrate in the tank. This is not so much to aerate the concentrate as it is to keep the concentrate cool throughout.

For aeration, we use no-clog spray nozzle heads for sap coming out of the electric releaser into sap tanks. We've done it this way for several years. https://www.youtube.com/watch?v=9XxR8VzFiH4

[DocsMapleSyrup]

What does the aeration do for the sap? Sorry if it's a dumb question.

[DrTimPerkins]

Aeration adds oxygen to the sap, which comes from a very anoxic environment in the tubing. This changes the type of microbial flora which grows in the sap, and tends to make darker, but better tasting syrup towards the end of the season. Not a huge amount of research has been done on it yet.

[bryan.22]

Is there any issues with running refrigerated Concentrate into a Steam Away?

Does the refrigerated sap need to be trickled into the evaporator to keep the boil from slowing down to much?

[bryan.22]

Does feeding refrigerated sap/concentrate from a Milk tank into a Steam Away cause any changes in the process?

[Bucket Head]

Dr. Tim,

The aeration is only done on incoming "straight" sap, and not again when the concentrate is going into the bulk tank? The air is not "lost" or lessened during ROing? Or would concentrate benefit with another aeration nozzle at the concentrate discharge? Anything we all can do to help our late season sap will help. Especially on seasons like this years!

Thanks.

Steve

[DrTimPerkins]

Is there any issues with running refrigerated Concentrate into a Steam Away?

Does the refrigerated sap need to be trickled into the evaporator to keep the boil from slowing down to much?

It can certainly be a good bit colder and can slow the boil in the inlet partition unless it is preheated. Likely the same would happen in a Steam-Away.

[DrTimPerkins]

The aeration is only done on incoming "straight" sap, and not again when the concentrate is going into the bulk tank? The air is not "lost" or lessened during ROing? Or would concentrate benefit with another aeration nozzle at the concentrate discharge? Anything we all can do to help our late season sap will help. Especially on seasons like this years!

So far we are only doing aeration of the incoming sap. Very likely aeration of the concentrate would also help, but there isn't any research on it yet. Our RO out stream is slow (but very sweet), so probably not enough pressure to really aerate it much, but it could be done another way.

[Tmeeeh]

We have a 1600 gallon mueller milk tank, submarine shaped with a manway on the top. The cooling heat exchangers in the tank are questionable. One doesn't hold pressure, the other seems to. I spoke to a dairy milking system installer who recommended not using the heat exchangers in the tank but use an external chiller to cool the concentrate as it goes into the tank. He claims that the concentrate temperature will rise only about 1 degree per day in the insulated tank. Apparently many dairy farms are doing it this way. We anticipate sending 300 to 500 gallons of concentrate to the insulated tank per day when the sap runs. Another option would be to recirculate the concentrate from the insulated tank to the chiller and back to the tank. Is anyone doing this with concentrated sap?

[WMF]

What type of chiller did the dairy guy recommend? I know it is common for dairies to use a well water powered plate cooler to lower the temp into the 60 degree range and then they use refrigeration to get milk down to upper 30 degree storage.
For concentrate you will want to be in lower 30 to upper 20 range.
I have been told that plate type coolers used in dairies will leak between the two fluid paths so you should not use chilled glycol to power one for maple concentrate.

[minehart gap]

Hey Steve ... Not sure exactly what you're looking for, but sap/concentrate spoilage is a function of time, temperature, sugar concentration and initial microbial load. We have done studies on it, with the following general results:

- warm sap spoils faster than cold sap
- higher sap sugar spoils faster than lower sap sugar
- sap spoils more the longer it is left out
- if sap has a lot of microbes to start with, spoilage will be faster

The colder it is kept, the longer it will last, but there is no single setpoint that we can say after this it is bad. Somewhat depends upon the types of microbes in the sap and aeration to some degree as well.

Dr. Tim, I believe that virus, bacteria and fungi are all consider microbes, that said, what types of microbes are you finding in the sap? I should reword that, are you finding more than bacteria and can it be assumed that natural yeast is present? We typically hear of sap containing bacteria but you using the microbes term is throwing me off. I am fairly certain that there are no virus in the sap but after this past year nothing should surprise us about a virus.

I believe what Steve is looking for and would be great to have is a graphic calculator (I can not remember the correct term for a line graph typy calculator with three axis) saying at a particular sugar concentration and a particular temperature, sap will stay good for this amount of time before the bacteria makes the sap spoil. Sounds easy, I have no idea how to do it though.

[Tmeeeh]

What type of chiller did the dairy guy recommend? I know it is common for dairies to use a well water powered plate cooler to lower the temp into the 60 degree range and then they use refrigeration to get milk down to upper 30 degree storage.
For concentrate you will want to be in lower 30 to upper 20 range.
I have been told that plate type coolers used in dairies will leak between the two fluid paths so you should not use chilled glycol to power one for maple concentrate.

The type of chiller he's recommending is a self contained refrigeration unit with a small tank containing a water/glycol solution in it. The glycol is cooled by the refrigeration unit and is circulated through a jacketed tank (perhaps a milk tank could be used). Another option is to use a plate heat exchanger to run the glycol solution and the concentrated sap through. Maybe a brazed plate heat exchanger would be less likely to leak. These units are commonly used for beer and wine making. Some are 3 phase and run by VFD. Here is an example https://www.advantageengineering.com/breweryChiller/units/glycol-chiller_BG-3A.php
There are used ones for sale on the beer and wine used equipment lists.

I suspect the dairy guy I talked to suggested the chiller because there refrigerant circuit is simpler and less likely to leak than sending refrigerant into an old milk tank evaporator cooling circuit. The chiller has one or two pumps to move the cold liquid around, probably draws more amperage and costs more.

[DrTimPerkins]

I believe what Steve is looking for and would be great to have is a graphic calculator (I can not remember the correct term for a line graph typy calculator with three axis) saying at a particular sugar concentration and a particular temperature, sap will stay good for this amount of time before the bacteria makes the sap spoil. Sounds easy, I have no idea how to do it though.

Unfortunately there is no simple answer. Spoilage is related to time, temperature, sugar concentration and microbe type and level. Time can be controlled by processing quickly. Temperature can be controlled with a refrigerated bulk tank or other ways (open-top tanks, tanks in the shade, snow, etc.). Sugar concentration means that when you concentrate you'd better plan on either refrigerating it quickly or keeping it very cold. Microbes (a catch-all term for all types of things: bacteria, fungi, molds, yeasts, etc.)...and there are many dozen dominant types that can be found...vary by year, time of season, operation, cleaning procedures, collection methods, storage methods, filtering methods, microbial load upon collection, processing factors (like double-passing or recirculating through the RO), etc. Just too many things going on to be able to provide solid predictive tools. Any tools we could provide would provide a false sense of security for people who might think it was OK to store the sap for a certain time period, then find out it was not OK.

What we do know is that spoilage tends not to be linear, but rather is exponential, so the longer it goes the faster it gets worse. Sap might seem fine one day, but be bad very soon after. It might be fine sitting around for 2-3 days early in the season, but not even make it a day in the later season.

There is unlikely to ever be a calculator that will tell you it is OK to keep sap for XX hrs, after that it is too late. In general, the longer it is held, the higher the invert level, the darker the syrup, and the greater the chance of other issues (off-flavors, sour, ferment, etc.) or ropey sap/syrup.

[WMF]

I have looked at the brazed heat exchangers and have always been concerned with the inability to clean them. From my research the shell and tube type seem to be the best sanitary style but food grade ones are very expensive.
There are cheap stainless and titanium ones all over the internet for heating pools but they are not food grade. Not sure if they would be "food acceptable" like some of our other equipment or not.
A lot of the cheaper glycol chillers out there are not rated to chill down to the mid twenties or to be used in freezing or sub freezing ambient temps so do some research.

[Bucket Head]

Yes, I was looking for a chart/graph/calculator/anything saying if your concentrate was at "x" percentage, then your refrigeration should be no higher than "x" temperature. I was trying to gauge if my holding temp. (and anyone else who knew what their exact concentrate and temp. was) was good or not so good. I did not know if any benchmarks were out there or not. And I can see why there isn't anything out there, with all the variables that Dr. Tim listed. I guess I'll have to end on cleanliness is key and colder is better!
Thanks for the replies, guy's.

Steve

[Shaun]

My bulk tank cools only to 34F and I had no issues keeping clear 14% concentrated sap for~70 hours this year. That said we went 6 days without a freeze towards the end of this season and I boiled out and cleaned tanks everyday out of concern of sap spoilage. IMO the preloading of bacteria in the sap might be the largest contributing factor to spoilage when using a refrigerated tank. If the sap is bad to begin with freezing it will not make it much better.

According to the chart a temp of 29F would be ideal for my setup, but I am not going to worry about a few degrees.

[minehart gap]

In general, the longer it is held, the higher the invert level

This is an interesting comment. I know that I am only using part of your sentience and I hope by my doing that, I am not taking it out of context.

It appears that you are saying that invert sugar level is related to quality of sap. Is this true? What level in the sap constitutes bad syrup?

I believe that invert sugar levels are the measure of12 molecule sugars that have broken. I am assuming that the bacteria is what is breaking them. Am I even remotely correct? And by introducing oxygen, I would think that aerobic bacteria would increase but that doesn't make sense because more bacteria mean faster bad sap. What do I have screwed up in my thought process here?

[DrTimPerkins]

It appears that you are saying that invert sugar level is related to quality of sap. Is this true? What level in the sap constitutes bad syrup?

I believe that invert sugar levels are the measure of12 molecule sugars that have broken. I am assuming that the bacteria is what is breaking them. Am I even remotely correct?

The "energy" derived by living things is held in the bonds of different chemical structures. You can kind of the energy as rubber bands that are stretched around and holding different elements or groups of elements together. Microbes (or people) add a little energy to that bond to the point where it breaks the bond, releasing the energy and transferring it to other chemical bonds. A rather simple way of looking at it, but close enough.

Sucrose (by far the dominant sugar in maple sap) is a 12-carbon sugar. It is pretty much two 6-carbon sugars (glucose and fructose, collectively called invert sugars), that are held together by a bond. Microbes consume and break the bond holding the two 6-C sugars, releasing energy in the process.

What is left by the process are invert sugars (6-C). Only a rather small amount of invert is found even in sap that is quite contaminated with microbes -- generally up to a max of 2-5% invert even in the darkest syrup.

Invert sugars chemically react quite differently than sucrose with amino/organic acids. Generally these suite of reactions will result in color (darkening) and flavor development.

When you heat syrup, another darkening/flavor forming process occurs, caramelization. Fructose (a 6-C sugar) has a much lower activation energy than either glucose or fructose, barely above that of boiling sap/syrup. However some fructose can get entrained into niter, where it will brown and form strong flavors.

So altogether, more microbes = more invert = darker and stronger tasting syrup.

Unfortunately there isn't a set level where too much is bad and below that is good. It depends on lots of factors that vary considerably.

That's the simple answer...the reality is much more complex. There are lots of different organisms involved, some do good things, some do bad. It is kind of like with some microbes you get wine and others you get vinegar. Temperature is important in the rate of microbial growth as well -- as is sugar content.

Abby and I wrote a chapter on the chemistry of maple syrup in 2009. Unfortunately it is not available for free (the publisher needs to make money somehow). The abstract and some of the figures are located at https://www.semanticscholar.org/paper/Maple-syrup-production%2C-composition%2C-chemistry%2C-and-Perkins-Berg/29eca27b32d2d202cc8b5c4af04a709af4adee49#paper-header Basically it is all you NEVER wanted to know about the chemistry of syrup, unless you're: 1) a maple scientist, 2) a real glutton for punishment or 3) maybe just a bit touched in the head.

If you are in any of those groups, perhaps you'd enjoy grabbing a drink (made possible by happy microbes) and watching https://www.youtube.com/watch?v=NnanxblnBJ4&list=PLZP4fDl-nB9806BqBzubk9c86w-H_5IBv&index=16&t=1s


And by introducing oxygen, I would think that aerobic bacteria would increase but that doesn't make sense because more bacteria mean faster bad sap.

There has not yet been a lot of research on this, however the thinking is that vacuum tubing systems are very anaerobic (low oxygen). By aerating sap you are changing the level of oxygen and shifting the proportion and types of microbes in the sap. Many anaerobic microbes can give rise to poor flavor (fermentation, sour sap) and poor quality (slimy, ropey) sap. Aerating sap also increases the microbial conversion of sucrose to invert, so you do end up with a darker syrup, however the good strong flavors (especially caramelization) can mask or overcome potential poor flavors. Research is ongoing, and there are no strong recommendations as yet.

[bill m]

Is there any time before, during or after the RO process that UV sterilization would be of benefit? Would it help in holding concentrate?

[DrTimPerkins]

Is there any time before, during or after the RO process that UV sterilization would be of benefit? Would it help in holding concentrate?

Sure, but units that are really effective are also really expensive, so few producers use them. UV units made for water have very limited effectiveness. The thickness of the water (or sap) film around the unit and the flowrates are too high to achieve good kill efficacy.

[Tmeeeh]

I have looked at the brazed heat exchangers and have always been concerned with the inability to clean them. From my research the shell and tube type seem to be the best sanitary style but food grade ones are very expensive.
There are cheap stainless and titanium ones all over the internet for heating pools but they are not food grade. Not sure if they would be "food acceptable" like some of our other equipment or not.
A lot of the cheaper glycol chillers out there are not rated to chill down to the mid twenties or to be used in freezing or sub freezing ambient temps so do some research.

I found it to be less expensive in my situation to find a milk tank with a intact refrigeration system rather than use a glycol chiller. Less complicated, likely to have fewer problems operating it and less expensive. It looks like a used milk tank and compressor can be bought for about the same money as a new glycol chiller and heat exchanger.

[WMF]

I have been experimenting with running chilled glycol through the refrigerant jackets on a 2000 gallon Mueller for the last two years with good results.
This still requires a glycol chiller which can be expensive. I have a 1.7 ton chiller and it is none too big.
Most of the Muellers have two separate cooling paths. One in the bottom of the tank and another which is split between the lower part of the tank at each side about 4 o'clock and 8 o'clock.
The bottom plate is most important to a dairy user as small quantities of milk don't even reach the upper plates and it will not cool well if the bottom plate is not working.
You may want to find out which plate is not leaking in your 1600 gallon. If its the bottom plate you may get by with just refrigerating it as the btu's of cooling required is much less for a modest stream of cool concentrate than for warm milk.
If you have an unheated sugarhouse make sure any condensing unit you get has a crank heater and some sort of switching for the fans to keep the head pressure up in cold weather.

[Tmeeeh]

I have been experimenting with running chilled glycol through the refrigerant jackets on a 2000 gallon Mueller for the last two years with good results.
This still requires a glycol chiller which can be expensive. I have a 1.7 ton chiller and it is none too big.
Most of the Muellers have two separate cooling paths. One in the bottom of the tank and another which is split between the lower part of the tank at each side about 4 o'clock and 8 o'clock.
The bottom plate is most important to a dairy user as small quantities of milk don't even reach the upper plates and it will not cool well if the bottom plate is not working.
You may want to find out which plate is not leaking in your 1600 gallon. If its the bottom plate you may get by with just refrigerating it as the btu's of cooling required is much less for a modest stream of cool concentrate than for warm milk.
If you have an unheated sugarhouse make sure any condensing unit you get has a crank heater and some sort of switching for the fans to keep the head pressure up in cold weather.

It turns out that both the cooling paths in the 1600 gallon milk tank have leaks and won't hold pressure. I had hoped to send cold glycol solution through the bottom cooling path. I decided against using an external heat exchanger because of the risk of the concentrated sap freezing inside it and the expense. I found a 1000 gallon working milk tank with two three ton compressors and a self washing system for less cost than a new glycol chiller. The compressors have crank heaters. I will be using only one of them. Used glycol chillers are available on the winery, brewery and distillery equipment lists. It will be a challenge to mount the tank overhead to gravity feed into the evaporator with the steam away. Thanks for sharing your experience with the chiller. All of this reinforces the idea that we make our money in the woods and spend it in the sugar house! At 69 years old we are hoping refrigerating the concentrate will make for less frequent boiling days. This recent season we boiled fifteen days in a row!

[Shaun]

I put a Uni-Strut trolley system the full length of the sugar house attached to the collar ties and used it to lift a 625 gallon tank to the loft, it worked well and didn't cost a bunch. Depending on weight you might be able to use 3 or 4 trolleys or more to make it safe and spread the load. Good luck, you will be happy with the tank.

https://www.amazon.com/Genuine-Unistrut-P2950-EG-Trolley-Assembly/dp/B00KN9UA0S/ref=asc_df_B00KN9UA0S/?tag=hyprod-20&linkCode=df0&hvadid=168463824956&hvpos=&hvnetw=g&hvrand=16973791314248676237&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9058731&hvtargid=pla-305931538483&psc=1

[WMF]

22383
When you look into your concentrate tank and see this you have no guilt about waiting a few days to boil. This was 14 brix about 29 degrees and is just slushy on top with the agitator always running.
I ditched gravity feeding a long time ago and use an all stainless dairy/triclamp pump to feed the steam away with no regrets. Having the concentrate tank at ground level is safer in cold icy weather but every setup is different.

[Tmeeeh]

22383
When you look into your concentrate tank and see this you have no guilt about waiting a few days to boil. This was 14 brix about 29 degrees and is just slushy on top with the agitator always running.
I ditched gravity feeding a long time ago and use an all stainless dairy/triclamp pump to feed the steam away with no regrets. Having the concentrate tank at ground level is safer in cold icy weather but every setup is different.

There's no room in our sugar house for the 1000 gallon concentrate tank. Our existing concentrate tank is outside up on a platform. Definitely not safe climbing up there. However gravity works. Are you pumping directly to your steam away float box and circulating back to the concentrate tank or do you have a small concentrate tank overflowing back to the concentrate tank? How are you monitoring the level of remaining concentrate while you are boiling? We have been using a clear sight pipe visible from most anywhere in the sugar house .

[WMF]

I use electric level switch and motorized ball valve and pump directly into steamaway. I have a panel with flowmeter and bypass valve so I can adjust flow to a little less than steamaway is using and level control adds the difference.
The pump was fine tuned to be able to be dead-headed for a few minutes with no problem but that never happens much.
Only half of the sugarhouse is heated and I have the tank bulkheaded into the unheated part. We have running hot water to be able to take care of any freezing issues until the sugarhouse warms up from boiling.
I welded a fitting into the tank for a sight tube which I would not be without. Everything is set up to be easily drained when done boiling.
If i was wood fired and did not have a steamaway a lot more caution would be needed to feed the evaporator with a pump in my opinion.

[PiperHill]

Good morning,

I have a plastic tank «*250g*» for my sap not concentrated and it’s located outside , sometime early in the season it still very cold over night or maybe for few days. i’m always afraid to keep the sap and make a big ice cube . Can i drop a heated cable like the one for the gutter inside?

Thanks

[motowbrowne]

Good morning,

I have a plastic tank «*250g*» for my sap not concentrated and it’s located outside , sometime early in the season it still very cold over night or maybe for few days. i’m always afraid to keep the sap and make a big ice cube . Can i drop a heated cable like the one for the gutter inside?

Thanks

Nothing wrong with some ice in your tank. You wouldn't want the whole thing to freeze if it's full(but that's not likely), and keeping some heat tape around the valve isn't a bad idea. Personally I like when my tanks have a nice chunk of ice in them to cool the incoming sap and help keep it fresh.

[DrTimPerkins]

22383When you look into your concentrate tank and see this you have no guilt about waiting a few days to boil.

Looks familiar. :D Note however that cold will delay spoilage, especially if the sap/concentrate had a low microbial load to begin with, but it will not prevent it from happening altogether. I can tell you from experience that having to dump 500 gal of 35 Brix concentrate (~200 gal syrup) is VERY painful. Seemed like nothing we could do last year kept the sap and concentrate from going bad in the blink of an eye.

[Mean_Oscar]

How long will frozen sap and concentrate (0 to 10 F) last?

[Bucket Head]

As Dr. Tim mentioned, that time will vary, depending on the initial sap quality. I once held 12% concentrate for a week and it made great syrup. However, it was early season sap and was crystal clear. I didn't want to keep it that long, but it was bitter cold for a week and I didn't get any more sap. Late season sap probably would have been a different story. But just having the ability to hold sap and/or concentrate, for whatever reason(s), lowers the sugaring season stress level significantly!

Steve

[DrTimPerkins]

It's a difficult thing to predict given the number of factors. The main one, which isn't easy for sugarmakers to judge, is the level of microbes in the sap. The real problem is that once they get started, growth is exponential, so sap or concentrate can be just fine one day (or one week), but will have gone bad the next day.

[Mean_Oscar]

I need to clarify that question. These are 2 gallon and 5 gallon size batches in commercial freezers. I always figured frozen (0 F to 10 F) would keep indefinitely like orange juice concentrate (if it did not dehydrate and all of ours has lids). Or steaks or vegetables in a freezer. I have kept sorghum juice (20 Brix) frozen in a plastic bucket for several months and it was fine.

So the question better stated would be: would, say 6%, maple sap concentrate deteriorate in a month frozen brick hard? If there is a problem it may be the 2 1/2 days freezing and 2 1/2 days thawing when it is at the ice and water equilibrium of 32 F.

[Mean_Oscar]

Aside from experience, how do you decide if concentrate is "bad"? Appearance / opacity? Smell? Taste? pH? Brix decrease?