Archive for January, 2010
Today Polyscience made the demonstration that a non stired water bath cannot be as efficient as an immersion circulator. It is funny to see that Polyscience directly mentions Sousvidesupreme in the TAG of the article.
Polyscience video indicates clearely that a non stired water bath has a longer response time to reach the desired core temperature. Therefore, it is obvious that Douglas Baldwin cooking tables sould be used with care. Douglas Baldwin indicates in the Pratical Guide to Sous Vide “With all these digital controllers, I highly recommend setting the temperature offset (measured near the temperature at which you wish to cook) using a high quality digital thermometer. Indeed, at the default settings the thermistors used in the above controllers can easily be off 2–4°F (1–2°C)”.
Freshmealsolutions mentions clearely in the user manual of the SousVideMagic : “If you don’t have a proper food core temperature sensor probe, always cook at desired core temperature settings for the duration as specified by reliable recipes with an additional safety factor of at least 25% longer…”
In addition the manual indicates “The default settings are designed to overshoot 1 or 2 degree higher for safety reasons. You can reduce the overshoot by making your own PID adjustments. See the document “PID Tuning”.”
There is now some weeks I wanted to verify by myself if a sous vide equipment is more energy efficient than a “traditional” convection oven. Cooking sous vide some kind of meats can take even several days (for example 72 hours pork ribbs at 57°C). What are the electricity costs?
How to proceed to illustrate this point?
My first thought was to compare the quantity of energy used by a convection oven and an immersion circulator (or a PID controller) in order to obtain the same doneness (rosé) on a 1 Kg beef filet.
Therefore I purchased in a do it yourself shop a very cheap appliance (EUR 11) to calculate the quantity of energy used by an electrical appliance (“consomètre” – refer to the picture on the left).
Unfortunately this “consomètre” cannot be plugged to my convection oven (the electrical cables of the oven are directly connected in the wall. In other word I have no mains where to plug this “consomètre”.
Thus I have decided to restrict my test to the assessment of the amount of energy used during a cooking process of at least 8 hours at 60°C. The final goal is to determine the cost of such cooking process.
I will not spend any time on the scientific explanation between Power and Energy since the purpose of this blog is only cooking. Nevertheless, for those who want to refresh their mind about physics basics I recommend reading this small article.
In order to determine the price of the energy consumption of an immersion circulator during 8 hours at 60°C I took a round pot of 15 liters and filled it with 28°C tap water.
It took 22 minutes for the swid to reach the target temperature of 60°C at full power (2,170 W).
Then the swid was stable very fast (some secondes only). At this stage the total energy consumption was 0.74 KWh which represents 8 cents (in France, 1 KWh = 0.11 €).
During the next 8 minutes the swid was struggling with power variation in the range from 50W to 600W. I would say the average could be in the area of 300W.
After 1 hour (excl. pre heating) the power variation was in the range from 14W to 200 W. At this stage (1:20 hours incl pre heating) the total energy consumption was 1.06 KWh.
Then I covered the tank with a plastic wrap in order to avoid water evaporation and let the swid run for additional 7:25 hours. When I came back in the morning the result was amazing. Power variation was in the range from 11 to 25 W. Total energy consumption was 2.05KWh (8:45 hours incl pre heating).
For France this represents a cost of approx. € 0.22 (0.33$ with currency rate of 1€ = 1.5 $). Astonishing isn’t it?
Bruno Goussault’s DVD mentions a recipe of a pear cooked sous vide:
- 1 pear
- 30 g chocolate
- 20 g vanilla sugar (vanilla extract plus sugar)
The recipes mentions puting the pear sous vide and immerse the pouch in a water bath set at a temperature of 8O°C until the pear is “done”.
Their is no mention of the cooking time. I checked several times the pear before it becomes too soft and therefore decided to stop cooking the pear after 30 minutes. I chilled the pear and kept it in the fridge one day before serving it.
The result is a very nicely cooked pear but I can’t say this pear was something special. It was good but nothing amasing. I think the main advantage of this way of cooking pears is the possibility to keep them 15 to 25 days in the fridge (at the condition to keep them in the pouch). This is definitely a very good point for professionnals.