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TonyC

Freeze Dryers and Freeze Dried Food (Part 2)

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Host's note: this topic is continued from Freeze Driers and Freeze Dried Food (Part 1).

Hello everyone,

We are new to this discussion having just purchased and rec’d our freeze dryer a week ago. I have read with interest the exploits from all of you over the last 20 pages and simply want to thank all the participants for sharing their knowledge.

We have now completed our 7th batch of freeze dried food with great success (thanks in no small part to the knowledge obtained here). It has inspired me to give back as well. I have two thoughts to contribute to this discussion. The first is a warning and the second is an observation.

First the warning – Botulism

For anyone who has canning experience beyond making jams or jellies, you know the dangers of botulism. We use pressure cookers and proven recipes to insure we kill the bacteria before we can our food. These recipes include not only the ingredients, but the cooking pressure and the minimum time to cook the food. The “USDA Complete Guide to Home Canning” is the bible when it comes to this method of preserving food. A quick google search will turn of quote above will get you to the guide.

Why am I bringing this up? Because the bacteria that causes Botulism thrives in an oxygen deprived moist environment. Putting away food that is not completely freeze dried in Mylar bags or canning jars by pulling a vacuum or using O2 packets can potentially put you and your family at serious risk.

With the above said, we have successfully vacuum sealed dry staples for years by simply pulling a vacuum. We have also canned meats and stews with pressure cookers successfully, but we have always erred heavily on the side of caution. I urge you to do the same when you freeze dry your food. Err on the side of longer cycles to insure that the food you remove is completely dry (under 5% moisture content – the lower the better). If any of your freeze dried food has a frozen center and you store it in an oxygen free environment, you are putting yourself and your family at risk. Botulism is odorless and tasteless. And you won’t know that you are infected until you are ill. This is serious!

From Wikipedia

Botulism is a rare and potentially fatal paralytic illness caused by a toxin produced by the bacteria Clostridium botulinum. The disease begins with weakness, trouble seeing, feeling tired, and trouble speaking. This may then be followed by weakness of the arms, chest muscles, and legs. The disease does not usually affect consciousness or cause a fever.[2]

Botulism can occur in a few different ways. The bacterial spores that cause it are common in both soil and water. They produce botulinum toxin when exposed to low oxygen levels and certain temperatures. Foodborne botulism happens when food containing the toxin is eaten.

Prevention is primarily by proper food preparation. The toxin is destroyed by heating to more than 85 °C (185 °F) for longer than 5 minutes. It is not recommended to give honey to children who are less than one year of age due to the risk with this food. Treatment is with an antitoxin. In those who lose their ability to breathe on their own, mechanical ventilation potentially for months may be required. Death occurs in 5 to 10% of people.

In all cases, illness is caused by the botulinum toxin produced by the bacterium C. botulinum in anaerobic conditions, and not by the bacterium itself

Improperly preserved food is the most common cause of food-borne botulism. Fish that has been pickled without the salinity or acidity of brine that contains acetic acid and high sodium levels, as well as smoked fish stored at too high a temperature, presents a risk, as does improperly canned food.

Foodborne botulism results from contaminated food in which C. botulinum spores have been allowed to germinate in low-oxygen conditions. This typically occurs in home-canned food substances and fermented uncooked dishes.[10] Given that multiple people often consume food from the same source, it is common for more than a single person to be affected simultaneously. Symptoms usually appear 12–36 hours after eating, but can also appear within 2 hours to 10 days.

Although the botulinum toxin is destroyed by thorough cooking over the course of a few minutes,[19][20] the spore itself is not killed by the temperatures reached with normal sea-level-pressure boiling, leaving it free to grow and again produce the toxin when conditions are right.

2nd The Observation

Being the curious sort that I am I placed an Accurite Thermometer in my Freeze Dryer to see what was going on inside this great little box. I followed the cycles through the Freeze cyle and into the two hours into the Vacuum cycle I had previously moniotored the 3rd phase. I was surprised by what I found and had to go do some reading on freeze drying techniques to begin to understand what was happening.

I set the cooling cycle to 10 hours so I could achieve maximum cooling. Post Dry time was set to 12 hours.

See my observations in the table below. The temperature probe was placed behind the insulation disc seated on the bottom of the cylinder in front of the trays. I secured the temperature gauge to the door with a magnet. It was within inches of the sending unit inside the chamber.

I wanted to know how long it took to reach maximum cooling. The answer is 8 hours.

Best time to put in pre-frozen food? The answer is 1 hour. The temperature in the Freeze Dryer will be very close to the temperature of your freezer at that point.

I was amazed at how fast the temperature dropped when the vacuum pump first kicked on. The temps literally dropped dramatically by 11F from -39F to - 50F in less than 2 minutes. There was a frost line completely around the bottom of my door gasket from 2 o’clock to 10 o’clock.

I was equally amazed to see the internal temperature rise from -50F to +60F in 2 hours. The temps at the time in my garage were 62F.

I surmise that the chamber walls stay well below freezing while the food dries out above freezing in a near vacuum. I set my freeze dryer to reach below 10 mT for a few hours before completion in the hopes that the almost complete vacuum helps to sublimate the moisture in the food.

There is a great deal of engineering going on that I am not sure I completely understand. I fully expected to see temps well below freezing through all three cycles. This is obviously not the case.

All this said, I love the function that the machine brings to me. I think better understanding of the strengths and limitations of the unit will aid each of us in setting our expectations realistically, and insures that we optimize the machine to its fullest. We all want freeze dried food that is nutritious, and safe to eat. Understanding the process will only help us make intelligent decisions.

I hope my contributions are worth something to someone. Thanks again for this group leading the way.

Kindest Regards, Tony

Edited to change table to picture for proper viewing and cleanup text... I'm trying!

Table .jpg

Table .jpg


Edited by Smithy (log)
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Tony - Welcome to eGullet and to our FD thread. What a great first post! Thank you so much for doing all that temperature/cycle work. I have been trying to figure out how I could put a thermometer inside and still be able to see it to read the temps at various points throughout the process.

 

All I had been able to find out till now is that the heat should come on at ~500 mtorr and go off again at ~600 mtorr, at which point the pressure increases, the mtorr drops till it again goes below 500 etc. I was also told that the temp would go up and down from -50 to -5F during the cycling till the end when it will slowly rise to +50F. I had no real 'confirmation' of what exactly was happening. I am not sure what you saw was what I understood either but thank you for your work.


Edited by Deryn (log)

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For all "Newbies" and those experimenting.  i have put together a summarization of my experiences of what I now call

 

"Universal Laws for Freeze Drying".."UL's" for short.).  Listed below.

 

i.e. Things you absolutely cannot do without inducing a bad or failed experience.   I think this will keep a few others from making the same mistakes starting out like I have done in the past.

 

How do I know about these "Laws".. "I" have done them....."ALL" of them ..and Sadly..some more than once.. sorry to say.  LOL..

 

It's like one of those OTHER universal laws that exists... i.e.  You HOPE your bag of experience fills up BEFORE your bag of luck runs out.  lol  I think this UL applies here as well.

 

Mr. Mikes "Universal Law's on Freeze Drying"

 

1.    Never over fill the vacuum pump oil reservoir above the fill line.  The oil should be BELOW the fill line.

2.    Never leave the drain tube valve open while drying, Said action WILL blow out oil of the pump and ALL over everything.

3.    Loading more than 8 lbs of food in the trays will take longer to dry and have a huge ice build up that gets into the trays

       inhibiting tray removal.  Defrosting and re-drying will need to be done.

4.    Drying anything that is more than 3/8" thick or overlapping slices will not fully dry.

5.    Fatty-greasy items does not freeze dry. Pepperoni, sausage, Steak fat etc.

6.    High sugar items may and probably will not dry.. Siraccha, gummys...maraschino cherries etc.  Tray clean up is a mess.

7.    Drying bread items turn it into a crouton.

8.    Honey cannot be dried.

9.    Chocolate cannot be dried.

10.  Liquid items should be frozen flat in trays before inserting into the machine.

11.  Drying sick butter makes a HUGE mess.  Butter in foods is ok.

12.  Foods MUST be fully frozen for a full cycle for optimum performance of lyophilisation..(driving off water) i,e Ice creme etc

13.  Safety: Using an extension cord of 14 ga or less) WILL melt the plugs and connections over time and possibly cause a fire.

                    This is one law you DON"T want to ignore.  I recommend 12 ga cord as a minimum and preferably 10 ga cord-25'

                     length maximum (more on that one later)

14.  Extended periods of inactive time (not drying) with the door closed WILL cause extensive molding of the interior components...regardless

       of how "dry" you think it is inside the chamber.  "Note to self- Leave the door open".   (More on that later as well)

 

These are mine... Any other UL?

 

Mr. Mike


Edited by Mr. Mike (log)
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Botulism cannot grow under an Aw of 0.95 which far moister than even the most incompetently dried FD food. There's no remote concern for botulism when FDing.

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Aw info.. Here ya go..

 

See FDA link below for additional info or google AW for more info.

http://www.fda.gov/ICECI/Inspections/InspectionGuides/InspectionTechnicalGuides/ucm072916.htm

 

DEFINITION

The water activity (a w) of a food is the ratio between the vapor pressure of the food itself, when in a completely undisturbed balance with the surrounding air media, and the vapor pressure of distilled water under identical conditions. A water activity of 0.80 means the vapor pressure is 80 percent of that of pure water. The water activity increases with temperature. The moisture condition of a product can be measured as the equilibrium relative humidity (ERH) expressed in percentage or as the water activity expressed as a decimal.

 

Most foods have a water activity above 0.95 and that will provide sufficient moisture to support the growth of bacteria, yeasts, and mold. The amount of available moisture can be reduced to a point which will inhibit the growth of the organisms. If the water activity of food is controlled to 0.85 or less in the finished product, it is not subject to the regulations of 21 CFR Parts 108, 113, and 114.

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Kerry,

 

How did the strawberrys turn out?...

 

My previous experience was that they didn't do so well whole.. then again.. I was doing 10lbs at that time and it overloaded the machine with ice.

and the berrys were pretty big. 1" 1.5" in dia.

 

Were the biggest ones completely dry?..  I'd be interested if you could put those in a zip lock or vac seal and see if they get moist in the package over a few days time.

 

M


Edited by Mr. Mike (log)

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Here are a few things that I did to make our freeze dryer easier for us to use.  Hope this helps others.

First I labeled everything.  I used black on clear labels.  Here is the drain valve
Drain Valve Label.jpg

 

Here are the Freeze Dryer Controls

Control Labels .jpg

 

Next thing I did was build a little stand for the Vacuum Pump and label an oil catch cup in 1 oz increments.  This makes it easier to drain and replace an ounce from the pump after each Freeze Dry cycle, and to keep track of how many times I have drained and added the oil.  When the cup is full (on the 8th cycle), I do a complete oil change and empty the 5 gallon drain bucket.

Pump Stand n Cup .jpg

 

After reading of the horror stories on water being sucked back into the freeze dryer on this list, I decided to try to keep this from happening to us.

I placed a nice big 5 gallon Lowes bucket under the counter below the freeze dryer.  I then attached a couple of pieces of aluminum tubing (one with an inside diameter larger then the outside diameter of the smaller) that I had in the garage to secure the drain line high enough in the bucket so that I could dump the water the same time I complete a vacuum pump oil change (every 8th cycle).

 

It appears to work fine as the water was a good 8" from the tube after 7 cycles.

 

bucket and drain line - 2.jpg

 

I secured the tube to the bucket with 2 rivets. 

Bucket Rivets .jpg

 

Hope this is of benefit to someone...

 

Regards, Tony

 

 

 

 

Drain Valve Label.jpg

Pump Stand n Cup .jpg

bucket and drain line - 2.jpg

Bucket Rivets .jpg

Control Labels .jpg

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Kerry,

 

How did the strawberrys turn out?...

 

My previous experience was that they didn't do so well whole.. then again.. I was doing 10lbs at that time and it overloaded the machine with ice.

and the berrys were pretty big. 1" 1.5" in dia.

 

Were the biggest ones completely dry?..  I'd be interested if you could put those in a zip lock or vac seal and see if they get moist in the package over a few days time.

 

M

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Success! Decided to half the blackberries since they were quite large. Prefroze them and did an 8 hour freeze time and 8 hour dry time. Went to the all xxxmt with 5 hours left on the dry. I'm wondering if there is an indication that you could turn down the dry time and by how much? Maybe not worth gambling with?


Edited by thegrandmammy (log)

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I have run several cycles now and the only thing that got completely dry with one cycle were the bananas. Yogurt had cold spots near the berries, canned pineapple took two cycles as did the cantelope. Three pork loins had cold spots as well. I put them back in for two more hours freeze time. Is there a ratio to use for drying time? Can you over freeze food? Some of the canned fruit was done but most was not so I ran the whole tray again.

What if I'm not home when the cycle is complete. Does the ice in the chamber put moisture back into the food. Do I need to run some kind of cycle before removing the food? Thanks for any advise.


FD Newbee

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In response to Rett

 

Can you over freeze food? 

                        I assume you are talking about in the machine.. no you can't over freeze it.  You want it frozen. 

                        I have learned to freeze food to the machine default setting and just wait till the whole machine cycles to

                        the end for the "beeper" signaling it is done.  If you haven't overloaded the machine.  It should be completely dry.

                        If it's not dry.. run another heat cycle.

 

Some of the canned fruit was done but moist was not so I ran the whole tray again.    

                      The sugar content may be too high if it was in a syrup or you had too much volume of food in the machine for one drying run. 

                      When I do fruit, I run about 5 lbs max.. and remember to keep the thickness no more than 3/8" thick for best results.

 

What if I'm not home when the cycle is complete. Does the ice in the chamber put moisture back into the food.  

                     No when the water is driven out, it is frozen and will not re-enter the food unless the machine is shut off and

                     ice begins to thaw.

 

Do I need to run some kind of cycle before removing the food?

                     See my previous post  in part one last page (20) about running a short term heating mode to have the food/tray

                     warm hot  link here  so it doesn't collect a "frost layer"   For me, its just a precautionary measure ensuring the

                     product will not collect any more moisture while out of the machine.

 

Hope this helps

 

Mr. Mike


Edited by Mr. Mike (log)
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Tony - By any chance have you repeated your temperature test at all? The more I look at your chart the more I am confused by what appears to be happening temperature wise.

 

As I noted I was told that the temperature would cycle up and down for many hours between -50F and -5F and it was not till the drying was done that it would begin to rise to +50F. Secondly, I see your chart seems to be only for a 12 hour period - what food did you have in the drier on that run that it would dry that fast?

 

When I spoke to my contact at HR a while back he said that I should not expect my runs to be less than about 20-24 hours (though I had success at 16 hours on my first run (from start of freeze cycle to removal of food).


Edited by Deryn (log)

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Thanks Mike for the info. Could have been the sugar in the canned fruit. My ice cream sandwiches did not work either. They may not have been cold enough although they were in the freezer for two days. So to run just a heat cycle I need to put the food back in turn freezer to 0 and that will start the heat cycle for the 7 hour default, right? Does it need to run seven hours? Thanks again


FD Newbee

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Rett,

 

Higher quality ice creme seems to do better from my experience... even then if you "crowd" "IC samitches" you'll have "blow outs"  too thick via being pressed together and can't freeze properly or drive out water so it gets "boiled out".  If you use non canned fruit.. you'll prolly have better results.. i.e fresh or fresh frozen.

 

MM

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Pipsqueak wrote:
I saw in one of the earlier posts somebody mentioned they have a kill - a - watt meter running on their freeze dryer, but I can't Remember who it was. Have you ever checked the power factor when your unit is running? Mine runs about .4 when the heaters are off which seemed pretty low, but I didn't know what to expect.

PS,
I checked my Kill-A-Watt during the Freeze Cycle (no pump, no heaters) and it read 0.39. I checked it at final Drying cycle (pump on and heaters on) a got 0.7.

The beginning of the Freeze cycle uses 600+ watts but will drop to 385 watts after it gets going. First part of Drying cycle (before heaters turn on) is arounfd 685 watts. When the heaters kick on it draws 1200-1300 watts.

Hope this helps.

 

To TonyC and Deryn;
The difference between TonyC's temp measurement and what Deryn heard from HR "might" be the placement of the temp probe on TonyC's FD'er. Remember that the tray heaters turn on during the FD'ing process. The proble might be too close to the trays and are picking up the radiated heat from the trays and not the air temp of the chamber so it's not giving a good air temp of the chamber. Just a thought.

JimR

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<p>JimR

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Jim - Thanks. That should have occurred to me.

 

Just re-read Tony's post description about where he placed the thermometer and it was not on a shelf (where yes I would expect it to be heated) and it was not up top (heat rises) and it was not on the window proper where heat could come massing out of most, if not all, shelves - he placed it below the bottom insulation it seems - so I am not sure where one might get a real idea of what is going on. The only place left (which may not be feasible unless one had a stick on thermometer) would be along the sides at the widest point. Oh well. HR didn't answer me when I pursued that line of questioning (about temperatures) other than with that general -50 to -5F statement. I guess they got tired of my questions (not sure I blame them!).

 

I first saw the chart in the middle of the night and was excited. But, I think my brain was foggy at the time and I didn't notice the details very well. My bad. I am also terrible at physics - perhaps temperature and vacuums interact in ways I don't understand. Could well be.


Edited by Deryn (log)

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All,

 

I have made some proposals for organizing all the topics here for a reference guide for new to experienced dryers to use.

 

One section is to have a Food Tried n Dried guide.

 

This is a section where you can post your results for all of your efforts for ANYTHING you have dried.. good or bad results.

Link here  "Calling All Freeze Dryers" as a new topic in the Kitchen Consumer section. 

This is to keep the regular FD forum from being bogged down with this effort.

 

Outline for the Reference Guide is for the The Big Picture" for the reference guide.

Link here

 

This is for "us" and your inputs are needed

 

Input away!

 

Mr. Mike


Edited by Mr. Mike (log)

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We have at least one poster (yesterdays) who uses a different freeze-drier. I believe hers is a Freeze Dry Co. (formerly Northstar) model 2000 which was used previously as a florist's unit.

 

(ps apologies if I posted this information twice - hit post and thought it registered but can't find it now).


Edited by Deryn (log)

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I checked my Kill-A-Watt during the Freeze Cycle (no pump, no heaters) and it read 0.39. I checked it at final Drying cycle (pump on and heaters on) a got 0.7.

The beginning of the Freeze cycle uses 600+ watts but will drop to 385 watts after it gets going. First part of Drying cycle (before heaters turn on) is arounfd 685 watts. When the heaters kick on it draws 1200-1300 watts.

 

Thanks!  Those power factor readings seem similar to what I'm getting, but my power draw is a lot higher - about 1650 when refrigeration/heat/vacuum are all running.  My amperage reading is around 18.  The refrigeration cycle seems similar to yours, but my heater amperage and my vacuum amperage seem a lot higher.  

 

I think the heaters say 165 watt on them, and there are 5 of them, so that would be 825 watt just from the heaters, but it seems like when the unit is in the final countdown, the wattage goes down.  Maybe the heaters have some sort of thermostat on them?  I would think that if it really was running 825 watts in a vacuum chamber the shelves would get a lot hotter than they do.  

 

Maybe I can talk my wife into letting me get a Watts Up meter to find out what's really going on...


Edited by Pipsqueak (log)

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A Watts Up meter is like a kill-a-watt meter with a data logger. You could monitor the whole cycle and export the information to a graph to see what the whole cycle looks like. You would be able to see when the heaters kicked on and off etc. Unfortunately they're about $200 so it's hard to justify it just to see what a cycle looks like on the freeze dryer. :)

Maybe we should start a thread for the tinkerers among us trying to reverse engineer this machine.


Edited by Pipsqueak (log)

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