How Long Does Raw Sap Keep?

[Andy VT]

I'm looking for information on how long raw sap can be stored at what temperature.

It seems fairly widely accepted that it can go one week at 37 degrees F. But the great outdoors is not always 37 degrees F. Is there a chart for how long at what temperature? How long at 50F, how long at 60F, etc?

I found that "snowbanking" was only practical, well, when there was snow, which there wasn't always!

Andy

[hogisland42]

I have always been told to treat it like milk. How long would you leave milk out before you had to throw it away?

[Andy VT]

I have always been told to treat it like milk. How long would you leave milk out before you had to throw it away?

Haha, well, then I repeat my question for milk! I keep milk in the fridge for about a week, but I have no more clue about other temps than I do for sap. Though it might be easier to find a chart I suppose.......

Anyone know? Has anyone experimented? Anyone left your sap hanging on the trees for 3 days in 50F and had it still taste good?

[maple flats]

Too many variables. The biggest being temperature, followed closely by the sanitation practices. If in bucket collection, with good clean buckets 1 day is safe at 50F but barely. The best way to judge it is clarity, if the sap is still clear it's good,
However cloudy sap will still make good syrup, just not as much as when it was clear. Once it gets cloudy , that is caused by micro-organisms which are feeding on the sugar in the sap.
To keep sap fresh the longest you need to keep it cool.
I will not even attempt to make a chart for the progression of sap degradation, but Proctor may have one.

[berkshires]

I typically boil once a week, because it's a two hour drive from my home to my sugarbush/evaporator, and I work full time. If it's going to be crazy hot, or for other reasons, I may take a day off some weeks, but I typically boil weekends. So the sap is always in buckets until I come get it and boil it. Sometimes I have to dump a bucket of sap, but rarely. This year the only sap I dumped was at the end of season from some taps that were basically shut down, and had a half inch of mostly moths in the bottom.

Here are the days I boiled, and how warm it got in between
- 2/21 to 2/25 there were three days over 50, including one over 60. It also was in the 20s at night. Sap was fine.
- 2/25 to 3/9 (two weeks!) six days over 40, two days over 50, and one over 60. But many nights in the single digits, and most of this time was frozen solid. Sap was fine
- 3/9 to 3/13 three days over 40, two days over 50. Sap was fine. In fact, this was the first batch where I wasn't tossing ice from the buckets as I collected sap.
- 3/13 to 3/19 six days over 50, one day hit 70. Sap was fine. Some buckets getting a trace of cloudiness
- 3/19 to 3/26 most days were in the 50s. Sap was fine, though getting cloudy
- 3/26 to 4/2 four days in the 50s or 60s. Nearly all sap was at least a little cloudy. Many trees shut down. Had to toss one or two out of 25 buckets because sap was no good, but those buckets had at most an inch or so of sap in them.

Remember - if there's ice in your bucket, no matter how warm the air is, the liquid in the bucket is no way going to get over thirty-something degrees.

Hope that helps.

GO

[DrTimPerkins]

Too many variables.

That's the best answer. It is dependent upon time, temperature, storage conditions (tank cleanliness and type and aeration), and type(s) of microbes present. There are several reasons for the lack of clarity.

One reason is that different microbes have certain doubling times that vary. Growth (replication) in microbes is not linear -- it is logarithmic. Say for example it takes one cell 30 minutes to becomes 2. In the next 30 minutes they'll become 4. 30 minutes later you have 8, then 16, then 32, then 64.... So in a very short span of time growth becomes explosive under the right conditions. We're talking in the MILLIONS of microbes very quickly. Once populations build, that million becomes 2 million, then 4 million, then 8 million very quickly. Huge effect on the invert level in the sap (or concentrate) and the quality of the sap (and syrup).

Researchers (UVM Proctor, Cornell, Centre Acer) have done work looking at this on several occasions, but I think we're all a bit wary of giving any real estimates in writing because of the wide range of variables involved. We don't want people saying...."researchers said I had 5 days, but my sap was spoiled after 3."

Lastly, some microbes may cause sap to make dark (but good) tasting syrup, others will make horrible tasting syrup in the same time frame, and others yet will turn the sap ropey and unable to be processed. This, of course, depends upon time, temperature, collection conditions and storage conditions.

If you can tell me which microbe(s) you have, what the sap temperature has been from the time it left the tree to the time you processed it, and how long it's been since the sap exited the tree until boiling started, I can probably provide you a general answer. :)

So the best advice is ...treat sap as if it were milk, keep it cold, filter well, process quickly.

[Wannabe]

I typically boil once a week, because it's a two hour drive from my home to my sugarbush/evaporator, and I work full time. If it's going to be crazy hot, or for other reasons, I may take a day off some weeks, but I typically boil weekends. So the sap is always in buckets until I come get it and boil it. Sometimes I have to dump a bucket of sap, but rarely. This year the only sap I dumped was at the end of season from some taps that were basically shut down, and had a half inch of mostly moths in the bottom.

Here are the days I boiled, and how warm it got in between
- 2/21 to 2/25 there were three days over 50, including one over 60. It also was in the 20s at night. Sap was fine.
- 2/25 to 3/9 (two weeks!) six days over 40, two days over 50, and one over 60. But many nights in the single digits, and most of this time was frozen solid. Sap was fine
- 3/9 to 3/13 three days over 40, two days over 50. Sap was fine. In fact, this was the first batch where I wasn't tossing ice from the buckets as I collected sap.
- 3/13 to 3/19 six days over 50, one day hit 70. Sap was fine. Some buckets getting a trace of cloudiness
- 3/19 to 3/26 most days were in the 50s. Sap was fine, though getting cloudy
- 3/26 to 4/2 four days in the 50s or 60s. Nearly all sap was at least a little cloudy. Many trees shut down. Had to toss one or two out of 25 buckets because sap was no good, but those buckets had at most an inch or so of sap in them.

Remember - if there's ice in your bucket, no matter how warm the air is, the liquid in the bucket is no way going to get over thirty-something degrees.

Hope that helps.

GO

TONS of people do it just like this.

[Andy VT]

Believe it or not, these responses are actually pretty helpful!

Berkshires: That's amazing! I am not remotely considering pushing things to those limits, so that makes me feel better if you're getting good results in those conditions. I have one question: Do your buckets hang on the trees or sit on the ground? I have a theory that buckets on the ground stay a bit cooler. One comment: you could find frozen sap on Friday afternoon that spent Monday through Thursday at 60F, but I get your point about ice being a good sign!

Dr.Tim: That makes sense! I would think, though, that a study could be published with all sorts of caveats saying "well, here is what happened when we did x,y,z; variables include but are not limited to G through T" (most maple studies I've read are pretty much like this anyway, and understandably so), as opposed to "you can expect X when Y". Maybe a study is even out there; I haven't searched too exhaustively yet.

One guy I asked who never deviated from buckets on spiles and other mid-20th-century methods from childhood until now says "3 days as long as its not like 70F". That's not very scientific, but I've got that bit of data in the mix as well.

I do plan to boil as quickly as possible, but also thinking next year I'm not going to spend much time snow banking. It turned out to be somewhat time consuming and I'm thinking that time might be better spent bringing sap to a boil, even if I don't have time to finish it. Boiling has got to kill a lot of microbes and increase shelf life by a lot, as would higher sugar content.

So, my question and your answers are helping me think through how I might size things according to how long and how often I think I can (and how often I think I must) boil down sap.
I've love to hear more sap shelf life experiences if anyone's got any.
(P.S., I've heard that bringing up to a boil more than once darkens the syrup. I'm becoming increasingly skeptical of this theory in batch processing. However, I do think, in batch processing, adding low concentration to high concentration sap during boiling does darken things considerably, and I see this done a lot)

[DrTimPerkins]

Dr.Tim: That makes sense! I would think, though, that a study could be published with all sorts of caveats saying "well, here is what happened when we did x,y,z; variables include but are not limited to G through T" (most maple studies I've read are pretty much like this anyway, and understandably so), as opposed to "you can expect X when Y". Maybe a study is even out there; I haven't searched too exhaustively yet.

Too many people either don't read or ignore the caveats or don't really know the conditions (temperature, exposure, microbes) to make it really useful.

As for research...yup, several places have done these types of studies. Not a lot published on it due to the reasons I explained earlier. However you might glean some info by watching https://www.youtube.com/watch?v=NnanxblnBJ4&list=PLZP4fDl-nB9806BqBzubk9c86w-H_5IBv&index=21&t=19s

[berkshires]

Believe it or not, these responses are actually pretty helpful!

Berkshires: That's amazing! I am not remotely considering pushing things to those limits, so that makes me feel better if you're getting good results in those conditions. I have one question: Do your buckets hang on the trees or sit on the ground? I have a theory that buckets on the ground stay a bit cooler. One comment: you could find frozen sap on Friday afternoon that spent Monday through Thursday at 60F, but I get your point about ice being a good sign!


I'm not sure I understand your point about Friday afternoon the day having ice in it.

Once there is more than a little sap in a bucket, there is a long lag time between air temp and sap temp. So if the average temp for a couple of days is more than a little below freezing, you are going to have a solid block of ice in your bucket. Once the temp warms up the sap will start to flow from the tree, but it's going into a bucket with a huge block of ice in it. Even on warm days, it will take days for that block to melt, and in the meantime it will keep the sap cold. And usually at night it freezes up again, at least partially. So the milk analogy is a little oversimplified. Often times the question is more like: how long will milk last if it has a ten pound block of ice in it. That is a very different issue.

Regarding hanging buckets versus ground buckets, certainly if there's ice or snow on the ground, you are right it may help keep them cold longer. I certainly pack the ground buckets in snow when it's available. But a much bigger factor in my opinion is that hanging buckets are open to the air. That means more contamination from the air and from bugs, and it also means more air circulation to warm up the sap faster on warm days. I've had many more hanging buckets go bad. The ones on the ground are loosely closed. The only thing that gets in is sap.

The other factor is sun. Buckets with sun on them can go bad very fast. Most of my trees are in the woods, where they don't see a lot of sun, but some southern facing buckets do.

Also, like Dr Tim says, good sanitation makes a difference. Given the doubling rate he mentioned, it pays to start out with a low number of microbes to start with.

Cheers,

GO

[Andy VT]

Very helpful discussion, thanks everyone!
Good point Tim... what would one even do with the information given all the variables. Same as now... boil quick as you can. I think my takaway is definitely boil quick as I can, but if life means a few days will pass, don't despair, it might be OK!
Regarding the sanitation... I know that the buckets should be nice and clean when the season starts, but do folks do any mid-season bucket cleaning? I did not this year, and by early April the buckets were disgusting, so I think I'll be doing at least one late-season cleaning of the buckets next time.
Oh, and Tim, that video is awesome! I'm only 15 minutes into it but taking notes voraciously! I'll be asking more soon about the tap hole closing and how much it indicates tree health...

[bigschuss]

I know that the buckets should be nice and clean when the season starts, but do folks do any mid-season bucket cleaning? I did not this year, and by early April the buckets were disgusting, so I think I'll be doing at least one late-season cleaning of the buckets next time.


I can't imagine the extra work involved in doing a mid-season clean. If you're talking 10 buckets in your backyard...sure. If you're talking 120 out in the sugarbush...no way. I'm guessing your buckets in April were disgusting because the season was long over. My season here in the Berkshires normally ends in early April and my buckets are generally fine.

One more comment about storing sap. There are times when I have my 55 gallon barrels half full of liquid sap and I throw in solid blocks of sap that froze in my buckets...and that sap will keep for weeks.

[Andy VT]

bigschuss, that is also super helpful info! I pulled my taps on April 6 when I got my first batch of yucky-tasting syrup. Up to then, tasted great. So, yeah, definitely end of season; but I had some doubts because the buds (sugars and norways) didn't bloom until at least mid-April and we had at least 2 more freezes before then. So, started to wonder if I should have cleaned and continued. But you're right, a mid-season bucket cleaning would be quite a bit of work! I probably could stand to improve my pre-season sanitizing.

[Pdiamond]

I start with clean buckets, and they do not get cleaned until the season is over. Some may get dumped out because of off colored sap but put right back on the tree. worry about cleaning after season.

[Biz]

Does the type of collection tank influence bacteria growth and therefore the length of time that sap can keep? Stainless vs. poly tanks or IBC totes?

Dave

[bigschuss]

I start with clean buckets, and they do not get cleaned until the season is over. Some may get dumped out because of off colored sap but put right back on the tree. worry about cleaning after season.

I agree. I clean when the season is over, and in the spring I simply grab my buckets and put them out. Never had a problem in 20 years. I see some go through the process of "sterilizing" their buckets. Seems like a lot of wasted energy.

[Andy VT]

I agree. I clean when the season is over, and in the spring I simply grab my buckets and put them out. Never had a problem in 20 years. I see some go through the process of "sterilizing" their buckets. Seems like a lot of wasted energy.

How are you distinguishing cleaning and "sterilizing"? Or put another way, how do you (all) clean your buckets?

[DrTimPerkins]

Does the type of collection tank influence bacteria growth and therefore the length of time that sap can keep? Stainless vs. poly tanks or IBC totes?

Yes. SS is easier to clean/sanitize and drain fully. Poly tanks/totes are difficult to clean and almost impossible to drain completely (most standard configurations).

SS Open-top tanks tend to stay cooler. Poly tanks and enclosed tanks will warm up.

[ennismaple]

Does the type of collection tank influence bacteria growth and therefore the length of time that sap can keep? Stainless vs. poly tanks or IBC totes?

Dave Sap spoils much faster in poly tanks and IBC totes. There's a lot more surface area for bacteria to grow and they are more difficult to clean than stainless. Those tanks also tend to be enclosed and hold in more heat - accelerating bacteria growth. We used a poly tank for concentrate for a few years and then switched to stainless and saw a significant benefit in sap/concentrate quality.

[Ed R]

I have a different sap collection strategy when I pass the mid point of the season. I never put my sap in a tank. I just collect into the 15- 20 food grade buckets and boil them as I go. I've found that sap goes bad faster when you throw it altogether.

[Andy VT]

I have a different sap collection strategy when I pass the mid point of the season. I never put my sap in a tank. I just collect into the 15- 20 food grade buckets and boil them as I go. I've found that sap goes bad faster when you throw it altogether.
Are you saying that this is something you start doing at the midpoint, and prior to the mid-point, you are collecting in tanks?

[DrTimPerkins]

I have a different sap collection strategy when I pass the mid point of the season. I never put my sap in a tank. I just collect into the 15- 20 food grade buckets and boil them as I go. I've found that sap goes bad faster when you throw it altogether.

The "one bad apple" theory. :D

[Ed R]

I use a small gathering tank and a storage tank when it is cold and sap keeps well. After that I just gather into 5 gallon buckets, snap on the lids, then haul them to the shanty. I do have a 7-8 gallon head tank that feeds my 2x6. All of my trees are within 125 yards of the evaporater. The Good Doctor is right, it just takes one bad bucket when mixed with 20 good ones to start a bad process. Late in the season it's better to leave the sap in buckets in the woods than to pick it up, put it in 2 tanks, then leave it overnight to boil a day latter. I will also turn over my buckets if it's an extended warm spell , sometimes do a quick wash, then put them back on when/if sap weather returns. I made some really good late season syrup this year when everyone around me had given it up.