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Puffed Snacks 1: Wherefore the Puff?

October 27th, 2009 · 32 Comments · Puffed Snack

posted by Dave Arnold

I love puffed snacks. Everyone loves puffed snacks. I thought it was time we posted on them.

Love

Why do things puff?

In the snack food industry, most puffed snacks are made from starch passed through an extruder.  A screw inside a long barrel mixes, compresses and cooks via friction all at the same time (sometimes extra heat is added, but often friction alone does the trick).  By the time the screw reaches the die at the end of the barrel the product mixture is very hot (well over 100°C) and under high pressure. When the product is extruded through the die at the end of the barrel this pressure is released and water boils off very rapidly –  puffing and drying at the same time. We don’t have an extruder at school, but that doesn’t keep us from making puffed treats.

The products we puff in the kitchen are technically glasses: amorphous (non crystalline) homogenous solids that are stable and rigid.  They also contain water (ideally about 12%).  All glasses have what’s called a glass transition temperature at which they go from rigid to rubbery.  This temperature is usually a good bit (like 100°C) lower than the melting point where they’d become a liquid. For foods destined to be puffed snacks, the glass transition temperature is ALWAYS higher than the boiling point of water –here’s why: When you heat the glassy pre-snack rapidly above 100°C the water inside wants to boil but can’t because it is trapped inside a glass.  When the snack reaches the glass transition temp it suddenly becomes rubbery.  The water is  able to start boiling and expanding,  which it does rapidly.  After the water boils away the product sets (because there’s no more water to keep it plastic and flexible) and becomes crunchy.

Points to remember if you want to do your own puffing:

  • The product you start with must be amorphous.  Crystals won’t puff.  As you will see, that is an important point to remember.
  • The water content must be correct.  Too little water results in burning and less puffing because 1) the temperature of the item will get too high before the glass transition is reached; 2) there is insufficient water to puff adequately; 3) without enough water the snack won’t be flexible enough to expand.  In the biz they say water acts as a plasticizer.
  • Other substances can also act as plasticizers – such as salt (which also helps taste and might help with heat conduction) and  maltodextrin — any relatively small molecule that will decrease the viscosity of your product.
  • Heat quickly and evenly.  I like frying, but air popping, heat guns and microwaves work too.
  • Don’t add things to the snack that will burn before the item is fully puffed –like sugar.
  • Don’t add things that will compete with the water in the snack and prevent puffing –like sugar.

Things that will puff fall into two main categories (that I know of): connective tissue and starches.

Connective tissue has lots of collagen.  When you cook collagen you break it into to gelatin, which is soft and easy to puff. When you dehydrate the broken-down connective tissue it turns into a glass, which you can heat and puff — a la pork rinds.  Wylie Dufresne works similar wonders with beef tendon and cod swim bladders.

Starches are made up of two main molecules: amylopectin and amylose, usually with more of the former.  Industrial puffing people care a lot about the amylose to amylopectin ratio.  In extrusion applications, about 50/50 gives the highest expansion.  The main structure comes from Amylopectin, while the amylose helps to increase the fluidity of the mix and increase expansion. The ratio  isn’t so important to us. What is important is that the starch gets cooked thoroughly. Native starch is partially crystalline and won’t puff.  The starch granules need to be fully cooked to ensure that the crystal nature is disrupted and the starch can become nice and amorphous.  Some chefs (like Wylie) use pre-gelatinized starch to get around this problem.  Mix with liquid, dehydrate, and you’re done.  If you want to go this rought use Ultra-Sperse from the National Starch Corporation. Don’t bother with Ultra-Tex – it’s hard to hydrate properly.

Almost anything that is mostly starch will puff: rice, corn, pasta, doughs made from tapioca starch (nice and bland), wheat starch, corn starch, yadda yadda.

How do you make a puffed snack?

Making puffs is as simple as: over-cook, dehydrate, and fry.

First: Over-cook your item.  In the case of starch this ensures that the starch granules are  fully gelatinized and at their lowest viscosity.  In connective tissue like pork rinds, overcooking ensures that all the connective tissue is broken down and soft.  Cook  pork rinds in very salty water for 60-70 minutes, pasta in heavily salted water for 45 minutes.

Second: Dehydrate. If the moisture content of your item is above 15% you won’t get much puffing.  If it is below about 10% you won’t get much puffing.  Most people don’t have the ability to test moisture content (If you are anal and you know your moisture level is close you can get it just right by sealing your stuff in a container with a saturated solution of ammonium nitrate or sodium nitrite in water.  That will maintain 65% relative humidity which will give a moisture content of 12%). In practice determining the moisture content isn’t usually a problem.  When the product goes from being flexible to being plastic-y and shrinky-dink like — you’re done.  Try puffing a couple and see what happens.  Over-dried stuff doesn’t bubble much when fried and burns without puffing. Under-dried stuff starts to puff and boils a lot but has a hard center that doesn’t puff.  You’ll quickly get the hang of it.  I recommend putting your product in the dehydrator at 135°F for a couple hours and then turning the dehydrator off and leaving the product overnight. In our kitchen this usually works.  If you live in a very humid or very dry place your results may vary (sorry Louisiana and Arizona). If you don’t have a dehydrator turn your oven on low and crack the door.

Here are pictures of some stuff puffing in a microwave ( thus the blurry pictures).

PorkRinds1

Pork Rinds puffing in a microwave

PuffStarch

Ultra-Sperse M and chicken stock puffing in a microwave

PuffPasta1

Pasta puffing in a microwave

Here is the technique for puffing pasta.  No, you can’t just puff dried pasta, you have to cook the heck out of it and then dry it.  I built a rack to hold the pasta while it was cooking and dehydrating because it was so fragile it wouldn’t hold its shape.  The pasta  almost breaks under its own weight it’s so soft.  You don’t need the rack if you don’t want to keep the holes in the pasta intact. After dehydration the pasta should have almost the texture it had before it was first cooked –just a little more flexible.

PastaMontage1

Put pasta on the special rack, salt the hell out of some water, boil the hell out of the pasta (like 40 minutes), load the rack into the dehydrator.

PastaMontage2

When the pasta has taken on the texture of a shrinky-dink, you fry it.

Here is the recipe for pork rinds:

Take pork skin and boil it in heavily salted water for 60-75 minutes. Carefully drain and cool in the fridge. After cold it is sturdy enough to handle.  Scrape the fat off the fat side; more scraping = better puffing.  Cut the pork rinds into pieces and dehydrate until they feel like plastic.  Fry in very hot oil.

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32 Comments so far ↓

  • Darren teoh

    Hey man, funny you should mention it. We just made some rice puffs this week for class.

  • novalis

    Couldn’t you check moisture content by weight? Weigh the product before hydrating, then weigh periodically during dehydration. When dehydrated weight = prehydrated weight plus 12%, you’re done.

    I guess that might not work for pasta, because you probably lose some starch to the cooking liquid, but it would probably work for pork rinds or especially ultrasperse-based puffs, right?

    • Dave A

      I was thinking about that. The problem is you’d need to know the initial moisture content of your flour, etc.

  • novalis

    Dehydrate the flour first?

  • Jason

    per the pregelatinized starch bit (ultra-sperse: yes, ultratex: no) what about Wondra flour?

    Arguably the name isn’t quite as high-tech (although it does sound magical!), but it’s pregelatinized and designed to hydrate easily.

  • Chocolatesa

    Wow that sounds really cool, AND something I could potentially do at home!

  • Stephen

    The rind of cheese puffs up into a light crisp puffy cheesy thing when microwaved, haven’t experimented yet but was wondering if any slice of cheese (hard cheese such as Parmesan) dehydrated would puff, or are there other factors at work creating the rind

    • Dave A

      Interesting. I don’t know. I read a study on puffing imitation cheese, but it only worked on low-fat/high-starch fake cheeses. Keep me posted on puffing real cheese.

      • Stephen

        Tried an experiment with 3 slices of Parmesan cheese (different thickness, thin to about 1.5mm).

        Dehydrated them, then put them in the microwave for 1 minute.

        The thinnest one didn’t really puff but but was super crisp.
        Next step up puffed up but was quite dense, crispy though.
        The thickest puffed up the best, good air bubbles inside, very crisp, and intense flavour.

        see pictures here
        http://www.flickr.com/photos/30576463@N07/4057066597/

        (please excuse quality but had to take them on cell phone as camera is on holiday)

        I think next, I’ll try a cheese with a higher initial water content.

        • chizzef

          How long and at what temp did you dehydrate the cheese? They look great, i would love to try!

          • davearnold

            Cheese rinds? They sometimes puff as is or you can dehydrate at 135 till they are plastic-y enough

      • Stephen

        sorry new user to flicker, I had accidentally set the photo to private oops! All fixed now.

        http://www.flickr.com/photos/30576463@N07/4057066597/

    • Chocolatesa

      Thanks 🙂 That looks yummy, I’ll have to try that myself.

  • chadzilla

    Awesome… all the way down to the little fork stand thing.
    Funny that we’ve been microwaving pork rinds in Louisiana for years, but never really thought it through further… cajun mind block.

  • AGP

    Haha! Jeremie showed me how to do this several months ago and now we use the pasta for our bar snack! Boil orciette pasta for 45 minutes, dehydrate it overnight in my convection oven, and deep fry it at 375. Wer toss our with smoked tomato powder!! YUM!!!!

  • Wylie Dufresne

    if you want to puff real cheese, try microwaving parmesan rind…

  • jeremiah bullfrog

    I’m gonna go make chocolate pasta..then puff it up.

  • Chocolatesa

    Stephen, the flikr pic doesn’t work, it tells me it’s a private page…

  • schinderhannes

    Off topic:
    it seems impossible to leave a comment on the ABV testing! One always gets to a 404 page.
    thus zip comments so far.

    Here is mine, you can either hang it there or I´ll restate it later:

    I would try to keep as many parameters under control and constant as possible.
    The main one seems to be concentration of taste contributing ingredients.

    Why don´t you try to make an extra concentrated dink (lots a lime etc) and then dilute always with the same amount of a neutral liquid. Either straight alcohol (200 proof from the pharmacy) or pure water or mixtures thereof.

    Thus in a pretty good approximation the only parameter changed is ABV.
    The art would be to make these drinks still taste half good. So I would start with a drink normally containing Vodka and replace that by an 80 proof mixture of water and alcohol. Then leave it out to get your stock solution.

    Schinderhannes

  • Danielle

    Have you ever seen those Hidden Valley commercials where there’s cauliflower popped like popcorn? It was on TV last night and I was just thinking how awesome it would be if you could have puffed cauliflower with ranch dressing.

  • hylan Joseph

    try steaming the pasta in a pressure cooker first,than frying it. A company I worked for years ago was trying to develop a pasta snack chip and this yields a pretty awesome puffed product.

    • nastassiar8se

      Great tip. Can’t believe I didn’t think of that.

    • sygyzy

      Steam it after dehydrating?

      • Dave A

        Hi Sygyzy,
        I don’t understand. You can’t puff by steaming after dehydrating unless you do it under great pressure (like an old school puffing gun). Steaming is a good way to gook out starch pasted before dehydrating. Tell me what you mean.

  • Jon

    So do you recommend using Ultra-Sperse rather than tapioca flour which is what a lot of other chefs use? Are there any percentages for Ultra-Sperse, or is it just by a “when it feels right” kind of way?

    • Dave A

      Hi Jon,
      Tapioca starch is made into a dough which needs to be fully cooked –usually by steaming. That technique works great. Ultra-Sperse is just made into a dough without cooking and is then dehydrated. Unfortunately, we just do it till it feels right. Janet Carver over at National Starch, the makers of Ultra-Sperse, might have a more accurate recipe.

  • Jimmy DeCaff

    I have experience making ‘shrimp chips’ from a shrimp paste and various starches. It got me thinking about making an artificial popcorn, as the only difference is that the corn kernel is hard and allows the pressure inside to build up, exploding violently. Step one would be getting the amylose to amylodextrin to protein ratio down. Any ideas for an edible coating that would allow pressure to build up?

    And completely off the subject (sorry), I am wondering about powdered fats. Why is it that I am always seeing tapioca maltodextrin used? I have some generic maltodextrin of both DE 10 and 20… Will either of these work the same way as tapioca maltodextrin?

    • Dave A

      Jimmy,
      The other interestig thing about popcorn is that we pop it in a raw state. We have tried pressure cooking popcorn, drying it and then popping it, but the pop is much less.
      Not all tapioca maltodextrins will work for the fat powder application. You need NZorbit from the National Starch Corp. That brand of tapioca maltodextrin is specifically designed as a bulking agent. The maltodextrin is in the form of a helix. The inside of the helix is hydrophobic, and absorbs fats. The outside is hydrophilic, so when you add water (or put it in your mouth) the whole thing dissolves. The helix structure of NZorbit isn’t unique, whst is special is its ability to bulk up, which is why fats can form powders and not pastes.

  • IVY

    we have machine puffing all food grain such as maize ,wheat and so on.
    If puffing rice , 10kg one batch and 60KG in an hour.this machine also can extend into procue wheat/rice bar line,and peanut/sunflower seed cake,coffee corn line and so on.

    This is the machine working video you can have an look.http://v.youku.com/v_show/id_XOTYzODg3NjA=.html

    The machine have CE certificate.we also supply some other snack food machine too,like:
    Bread machines;
    coffee corn line;Cornflakes,Breakfast cereals;
    Potato chips line ,bread,bean processing machine;
    Iron plate roast cake line ,french cookies line;
    Egg roll ,wafer/biscuit line .

    Any question just tell us.Best wishes,nice day!

    yours

    ivy
    International Department
    Mobile:86-013930146703
    Skype:ivy2028
    export_ivy at hotmail.com