DouglasBaldwin

As much as I like my chamber vacuum sealer, I would be just as happy using heavy duty freezer Ziploc bags for sous vide cooking --- I add about a quarter cup of liquid and use the water displacement method*. You are absolutely correct that the only reason to vacuum seal when cooking sous vide is to allow for the efficient transfer of energy from the water to the food. Moreover, O’Mahony et al. (2004) found that the majority of pouches after vacuum packaging had high levels of residual oxygen --- which means vacuum sealing does not necessarily reduce the risk of aerobic bacteria. * To quote the current draft of my upcoming book, "Sous Vide for the Home Cook": "To remove most the air from the bag: (i) fill a deep container (such as a pan, pitcher, or bowl) with fresh cold water, (ii) submerge the bottom of the unsealed bag in the water until only the sealable top is above the surface of the water, (iii) start sealing one side of the bag and feed the sealed edge under the water as you go, (iv) when you have finished sealing the bag, it should be completely submerged in the water, (v) remove the bag from the water and check that the seal is good and little or no air remains in the bag."

Pedro, I'm afraid you are quoting the caption to a table which I emailed you (and a couple others), but have never posted on here or on my web site. So, to keep everyone in the loop, I uploaded it to: http://www.douglasbaldwin.com/HeatingTimeGeoFactor.pdf. Note that the times are for the heating of thawed foods and not pasteurization. For pasteurization times -- which is what you will need when cooking poultry, meat, or fish -- please see the appropriate tables in my guide.* The linked table is only meant to give a reasonable time range for heating foods in a water bath and to show how sensitive cooking time is on the shape of the food. Very Best Wishes, Douglas * Note that all the pasteurization times in my guide assume the worst case scenario: the minimum reported thermal diffusivity for that food, a lower surface heat transfer coefficient, and that the shape is an infinite slab.

A couple months ago I contacted the manufacture of Ziploc (S. C. Johnson & Son, Inc.) and they told me their heavy duty freezer bags were safe up to 195F/90C. While I still use my chamber vacuum sealer for just about everything, I actually prefer Ziploc bags to the FoodSaver. I just add about a quarter cup liquid (stock, court bouillon, etc) to the bag, submerge the bottom of the bag under water to displace the air, seal and cook. So far, I haven't had a single bag fail --- but, I never had any of my FoodSaver or chamber vacuum sealed bags fail either.

It is really the change in pH that matters. I just suggest baking soda because it is a pantry staple. The only real problem with using baking soda, say to brown onions for a soup base, is that if you don't add an acidic component later you will have a soapy tasting soup.

Your oil was indeed too hot. If you are searing in a smoking hot pan with an oil with a high smoke point, I absolutely agree that you do not need or want a glucose wash. If, however, you have an anemic range or a light pan or a low smoke point oil, then a glucose wash will allow you to sear the meat at a lower temperature in about the same amount of time as your very hot pan. Therefore, I would only recommend using a glucose wash when searing in a 175--200C/350F--400F pan; when searing in a 200C/400F or hotter pan, I would not recommend using a glucose wash.

Stu, I'm afraid it wasn't anything as exciting as that. When browning meat cooked sous vide, we want brown the surface without overcooking any of the interior. Since time (primarily) determines how much of the interior is overcooked, we must brown the surface as fast as possible. For the fastest possible browning, we need amino acids available to react, we need reducing sugars available to react, and we need heat to get the reactions going. Martin (over at Khymos) showed how well baking soda improved the browning of onions by making the amino acids more available to react. In meat, we are more concerned with the availability of reducing sugars, so washing the meat with a reducing sugar (such as glucose or fructose or lactose) should speed up the reaction considerably --- this availability means we can brown as quickly in a (smoking) hot skillet as we can with a blowtorch. It happens that someone (Skog, 1993) already thought of washing the meat with a glucose solution to speed the reaction, so my only novel part is applying it to sous vide cooking. -- Douglas

In a sense, you are both correct. At lower temperatures (131--135F/55--57C), the enzyme collagenase is able to break down collagen into gelatin. Collagen which is not broken down my enzymatic actions will dissolve into gelatin around 144--145F/62--63C. To quote my guide:

You can also just cover the water bath with plastic wrap (with the plastic pressed down to the surface of the water).

There is no practical concern with reheating the food at or above 130F (54.4C). It would be prudent to reheat it in such a way that the core reaches 130F (54.4C) within 6 hours to prevent C. perfringens from outgrowing and multiplying to dangerous levels --- however, this requirement isn't very sharp and needs to be studied in more detail.

You can safely hold the food at -20C indefinitely. Eventually (after many years), you will develop some freezer burn on the food (since a very small amount of gas is able to permeate the plastic), but it will still be perfectly safe to consume. My only recommendation is to label the bags with a permanent marker so you figure out later what type and cut of meat it is and how it was prepared.

You are correct that the spores have not been destroyed --- the only way to destroy all the spores is to use an pressure cooker. You have, however, pasteurized the food --- that is, you have reduced all the vegetative pathogens (the pathogens which are alive) to a safe level. So long as you keep the food sealed in their pouches, they cannot be contaminated with additional vegetative pathogens. Thus, all you need to do to assure the safety of the sealed pouches of food is to prevent the spores from outgrowing and multiplying to dangerous levels. This is easily achieved by rapidly chilling the pouch in ice water and either freezing or storing at (i) below 36.5°F (2.5°C) for up to 90 days, (ii) below 38°F (3.3°C) for less than 31 days, (iii) below 41°F (5°C) for less than 10 days, or (iv) below 44.5°F (7°C) for less than 5 days. [Please see the safety section of my guide for more details and references to the appropriate scientific literature.]

What an interesting idea. I'm guess that it will work as well or better than water, but I won't know until I give it a try.

adey73: Yes it is post-cooking once it comes out of the bag. infernooo: So long as you don't add too much glucose or baking soda, it tastes just like traditionally seared meat, it just takes a lot less time (and heat) to achieve the same level of browning. One of the benefits of this method is that it decreases the production of carcinogens formed during the Maillard reaction (when compared with traditional cooking methods). To quote the recently expanded "Maillard Reaction" section of my guide: Edit: Added quote from my guide.

Like most of us, I use a (butane) blowtorch for most my searing. If you tend to overcook the interior of the meat when using a pan with smoking hot oil, you can use the following trick: (i) prepare a glucose wash (100 g water plus 2--4 g corn syrup), (ii) dry the surface of the meat and brush the glucose wash over the meat, (iii) sear in the smoking hot pan until nicely browned (say 20--30 seconds). If you do a side-by-side comparison, I think you will be surprised at how effective the glucose wash is at enhancing the Maillard reaction; note that it has to be a reducing sugar (glucose, fructose or lactose) and not table sugar (which is sucrose). You can also try adding a pinch of baking soda to the wash, since increasing the pH of the meats surface increases the availability of the amino acids which can react with the reducing sugars. Be careful though not to add to much baking soda or corn syrup, since baking soda can give a soapy taste if there isn't enough acid (on the meats surface or in the sauce) and too much corn syrup will give an unwanted sweetness.

That is an interesting question, I'm not sure why most studies do not consider anything less than 135F/57C in eggs or poultry; . For an educated guess, we can use the D-values for Salmonella enteritidis of 4.5 min at 58C and 6.0 min at 57C in [J Appl Microbio 83 (1997) 438--444]. These D-values give a z-value of 8C (1/log_10(6.0/4.5)). Therefore, at 131F/55C it would take 6.5*6.0*10^((57-55)/8) + 35 = 105 min and at 133F/56C it would take 6.5*6.0*10^((57-56)/8) + 35 = 87 min (where the study found that the egg took 24--35 min to come up to temp). From Table 4 of the survey article [J Food Sci 71 (2006) R23--R30] (which includes many studies at 55C, 57.5C, 58C, ..., 70C for Salmonella spp in poultry), I compute a D-value of 4.8 min at 60C with a z-value of 6.46C. Thus, a 6.5D destruction of Salmonella spp is: 6.5*10^(9.97- 0.1548*55) + 35 = 220 min at 131F/55C and 6.5*10^(9.97- 0.1548*56) + 35 = 165 min at 133F/56C. However, since Salmonella enteritidis (which is the strain found in eggs) is a less thermally resistant strain than the Salmonella senftenberg containing `cocktail' used in most the studies, the times in the previous paragraph should be sufficient. Edit: Added extra detail.

Sous Vide Hamburgers First off, there is no greater risk of botulism in hamburgers than other food products prepared sous vide. As stated up thread (and in my guide), to prevent the outgrowth and toxin formation of Clostridium spp. (e.g., C. botulinum and C. perfringens) either: (a) hold the food at or above 54.4C/130F until ready for service or (b) rapidly chill (in ice water), chill hold (at below 38F/3.3C for up to four weeks or freeze indefinitely), and rethermalize/reheat (at between130F/54.4C and the original cooking temperature) until ready for service. Can you pasteurize ground beef sous vide? You betcha! In fact, most the studies which determine the pasteurization times for beef use ground beef (which has been inoculated with a pathogen) and placed in either a vacuum bag or a test tube which is placed in a water bath controlled with an immersion circulator for a set length of time! Thus, you can pasteurize your hamburger using the times in Table 5.8 of my guide. You cannot, however, linearly extrapolate pasteurization times to temperatures lower than 131F/55C! From Table 5.8 in my guide, you can see that I use D_60^9.22 = 3.63 min; this means that at 55C/131F it takes 6*3.63*10^((60-55)/9.22) = 75.9 min or at 53C/127.5F 6*3.63*10^((50-53)/9.22) = 125.1 min. However, C. perfringens can grow and produce toxins at temperatures up to 127.5F/53C. Therefore, 54.4C/130F is the lowest practical temperature which meat can be safely held or pasteurized at.

You can also use a few drops of Corolase (from AB Enzymes). It will break down all the gelatin in the sauce in less than a minute, and you can then reduce it to your hearts content. It will not produce a clear sauce like syneresis will, but it is fast.

The reason Heston put the meat in a 50C/120F oven for 18--24 hours after searing the outside was rapid aging (also called conditioning). According to Lawrie's Meat Science (p. 239--240), meat held at 43C/109F or 49C/120F for 24 hours had a greater increase in tenderness than meat kept for 14 days at 2C/36F; he notes, however, that while the tenderness increase was particularly high at 49C/120F, it had a somewhat undesirable flavor. Without a doubt, this rapid aging is well within the real danger zone of -1.6C/29.3F to 52.3C/127.5F. Is there much danger if the surface of the intact beef muscle is pasteurized with a blowtorch or boiling water? If we can assume that the interior of intact muscle is essentially sterile, than it should be safe. How valid this assumption is when we don't know the provenance of our meat? I don't know. If you do plan on doing rapid aging, I would recommend the higher temperature (49C/120F) since all but C. perfringens stops growing by 50C/122F (and this is only because of the Phoenix phenomenon which (to the best of my knowledge) has only been observed in the laboratory).

Air (even forced convection air) is not sufficient for sous vide cooking. The heat transfer coefficient of commercial convection ovens is only about 15--30 W/m^2-C, compared to 300--10,000 W/m^2-C in water baths and convection steam ovens (also called steam retorts) [Nicolai and Baerdemaeker, 1996]. So, when cooking in a water bath or a steam retort, the surface comes up to your desired core temperature almost immediately --- the same is not true in convected air. Indeed, you can reach your hand into a 400F/200C oven without getting burned, but you wouldn't think of plunging your hand into boiling water (even if it is 200F/100C cooler)!

The MVS31 has no trouble compressing fruit. Edward is spot on in his discussion about the power of different vacuum pumps; how strong the vacuum is depends much more on the type of pump than its power. As for speed, I find that the MVS31 can vacuum seal the bags faster than I can fill them.

The chamber is quite easy to clean --- it is very easy to remove and replace the seal bar. I won't need to change my oil for another year, but it looks quite easy (it certainly doesn't require to flip the machine upside down!). While you can open the lid about 8in with a cabinet 24in above the counter, you would have to hold it open while you position the bag; if you had 28in from counter to cabinet, the lid could be opened all the way. Personally, I put it on a sturdy stand at the end of my counter (since I already lost enough counter space to all my water baths!).

I also have a MVS31 (but from this guy) and love it. I haven't used any other chamber vacuum sealer, but it seems very well made and its digital controls are very easy to program and use. It is definitely a space hog, but I suspect that the same is true of any chamber vacuum sealer of usable size.

As with everything, it depends. Let us first consider taste and texture. The very best taste and texture is from cook-hold* sous vide cooking. Depending on how long the food will be stored, either cook-chill or cook-freeze** will be better. For short storage times, cook-chill is often better than cook-freeze because freezing can damage the cell structure of the cooked food and alter its texture. For longer storage times, cook-freeze is often better because spoilage microorganisms (which often survive pasteurization) and warmed-over-flavor (WOF) can increase to unacceptable levels at chill temperatures. Repeated cook-chill/freeze processing would only exasperate these issues. From the food safety perspective, I would also not recommend repeated cook-chill/freeze processing. The problem is not from vegetative food pathogens, but from spores outgrowing and producing toxins during the repeated rapid chillings and heatings. I cannot easily say how many times you could safely repeat the cook-chill/freeze process because it depends on the rate of heating/cooling, the type of spore-forming pathogen present in the food, and the chemical properties of the food. (See my guide for more details on food safety.) In summary, I would recommend avoiding repeated cook-chill/freeze processing. * Cook-hold: vacuum sealing the raw ingredients, heating to your desired core temperature, (holding at that temperature until pasteurized,) finishing and serving. ** Cook-chill/freeze: vacuum sealing the raw ingredients, heating to your desired core temperature, holding at that temperature until pasteurized (for a 6D reduction in Listeria), rapidly chilling to limit sporulation, store in a refrigerator below 38F/3.3C for less than four weeks (or freeze until needed), reheat in a water bath at or below the original cooking temperature (typically 131F/55C), finish and serve.

I agree with you Sam. Many studies have shown that oil does not penetrate the fries during frying, but during the cooling period after the fry is removed from the oil. In general, the final oil content is proportional to amount of moisture lost during frying; so, decreasing the thickness, increasing the frying time, and/or increasing the temperature will all increase the final oil content.

While they are certainly pasteurized, they are not shelf-stable or sterilized. Since many spore forming microorganisms are found in dirt, we cannot assume that the potatoes will be essentially sterile (as we often do with the interior of intact muscles meat). Indeed, a dozen or more academic journal articles mention B. cereus and Clostridium spp. spores in potatoes prepared sous vide. Thus, I would recommend rapidly chilling the potatoes (in the vacuum pouch) and storing below 39F/4C to prevent the outgrowth and multiplication of B. cereus. Edit: Fixed typo.