Comparing the Cost of Cooking Using a Slow Cooker & a Thermal/Hay Box Cooker - Energy Prices October '22

[GadgetGal]

October ’22 Energy Price Cap – Cooking with a Slow Cooker Compared to a Thermal Cooker/Hay Box

(Costs using the 'new' October '22 Price Cap are for direct debits. There are a few 'regional' minor variations and the costs for pre-payment meters and 'credit' payments are different.)

I first learned about hay boxes nearly 50 years ago but only got around to using one about 3 years ago.
For convenience, I bought a MrD thermal cooker - the vacuum type. They are very robust and puncturing/breaking them would be quite difficult, even if you tried.

All of that said, 2 years ago, I needed to make a meal for 20 people to be eaten outside (10C outside temperature). Obviously, the Mr D one wasn't big enough for that so I made one by using a cooler box.
I added bubble wrap in the corners to prevent heat escaping from gaps and lined the 'pan cavity' with aluminium foil so the bubble wrap didn't melt from the heat of the pan. I used a 10L SS stock pot in my DIY cooker, adding a cushion on top of the pan lid before putting the cooler box lid on. I used both the MrD and my DIY cooker (pasta bolognaise in one and lentil & veg soup in the other. Both were steaming hot 7 hours later, everything was cooked to perfection.

You don’t need a cooler box or cooler bag (although the in-built insulation makes it easier to construct); you could make one from other recycled items such as a cardboard box or laundry basket with an old duvet, woolly jumpers etc. as insulating material … or literally, a box filled with hay. You can also sew one like a Wonder Bag (filled with polystyrene balls); if you Google thermal cooker or Wonder Bag, you can find free patterns. Thermal cookers are VERY energy efficient (see below), easy to make, portable (you can take it anywhere), safe (no worries about leaving an electrical appliance on if you’re out) and they make a great science or craft project for children.

I also did some research recently to compare cooking a stew/casserole with a slow cooker and a thermal cooker. If using a thermal cooker/hay box you need to: have the pan at least 80% full; bring to the boil & then rapid simmer for 10 minutes to create an on-going 'food safe' cooking temperature (it needs to be maintained at over 63C).

I estimated a total of 15 minutes on the hob for a thermal cooker and if using a *slow cooker, 1 hour on high and 6 hours on low - as per most manuals. (*I researched dozens and used an average of 12 'typical' slow cookers - I excluded multi cookers because wattages varied too much.)

Findings (using the 'new' October '22 price cap):

Gas – 10.33p kWh; Electricity – 34.05p kWh

Slow cooker – ‘High’ 210W x 1 hr = 7.15p & ‘Low’ 207W x 6 hrs = 42.29p; Total cost = 49.44
Thermal cooker – using gas hob for 0.25hrs – 2.58p (Saving 46.86p and 19x cheaper than a slow cooker)
Thermal cooker - using electric 2.3kW hob for 0.25hrs – 19.58p (Saving 29.86p and 2.5x cheaper than a slow cooker)

I hope the above makes sense and you find it useful and interesting. I must admit, even I am surprised at the cost saving when using a gas hob for the initial 15 minutes cooking time!

[jennyjj01]

Awesome. Thanks.
The time you quote for a slow cooker is similar to what I'd use cooking a small joint of meat or a chicken casserole. Would the haybox idea cook a joint, because presumably it would not be simmering.

[Norma]

There’s a book called ‘The Fireless Cook Book’ that’s available. I’m not sure if it’s an adapted version of the one published in 1913 but you can buy it new or on 2nd hand bookshops. Personally:

1. I’d be very wary of cooking a whole joint or chicken like this because there are minimum temperatures that have to be maintained to be regarded as safe, preventing bacteria growth in meat. You couldn’t be sure that these were obtained and maintained in all parts of the bird or joint over several hours
2. I’d boil a meat stew at the end of the cooking time for a few minutes to raise the temperature and ensure bacteria are killed off

There’s loads on the internet about safe cooking with hayboxes.

[GadgetGal]

Awesome. Thanks.
The time you quote for a slow cooker is similar to what I'd use cooking a small joint of meat or a chicken casserole. Would the haybox idea cook a joint, because presumably it would not be simmering.

Not something I've done personally but from what I've read and looking at YT videos, you can and many people do cook a joint in a hay box. There are 2 methods:

1) Sear the joint then put lots of veg underneath and around the joint, then follow the 'usual rules' re. 80% 'rule' and boil/rapid simmer. This is a recipe for pot roast sirloin: https://mrdscookware.com/recipe/pot-roast-beef. This is the most common way of cooking a joint in a thermal cooker.

2) Sear the meat before cooking; then wrap in foil - if you don't want the veg, place a trivet in the bottom of the pan and follow the 'usual rules' or place the joint, wrapped in foil on top of veg and 'follow the rules'.

If you want your joint to have a more 'crispy' outside, you could sear the meat again after thermal cooking but obviously, your energy usage would increase too.

One other thing with a thermal cooker, if you don't have any electricity or mains gas, you could do the initial cooking on a BBQ or camping stove - some people take them camping to save on fuel usage. (My daughter is going on a 5 day survival course in October where thermal cooking will be used for some of the meals' - including venison.)

There are a few recipes for different things here: https://mrdscookware.com/recipes

I've also seen YT videos of bread cooked in a thermal cooker. It is 'crustless' but still looks spongy and fully cooked.

This is an excellent video I found recently that gives a bit of the history of thermal cooking and demonstrates 2 soups and bread being cooked. Well worth watching: https://www.youtube.com/watch?v=4dlbbCAHzrc

[GadgetGal]

There’s a book called ‘The Fireless Cook Book’ that’s available. I’m not sure if it’s an adapted version of the one published in 1913 but you can buy it new or on 2nd hand bookshops. Personally:

1. I’d be very wary of cooking a whole joint or chicken like this because there are minimum temperatures that have to be maintained to be regarded as safe, preventing bacteria growth in meat. You couldn’t be sure that these were obtained and maintained in all parts of the bird or joint over several hours
2. I’d boil a meat stew at the end of the cooking time for a few minutes to raise the temperature and ensure bacteria are killed off

There’s loads on the internet about safe cooking with hayboxes.

I've got a PDF version of The Fireless Cook Book - it's very useful and interesting, (not looked at it for a while though).

Regarding the safe cooking - there isn't a problem keeping cooking at over 63C (the 'safe zone') - this is why it's essential to have the pan at least 80% full and rapid simmer for 10 minutes. It kills off pathogens/bacteria and creates enough thermal mass to continue cooking safely ... PROVIDING ... your insulation is adequate i.e. if you can feel heat from the pan on the outside of your insulated container, you either don't have enough insulation or it's poor insulation. It's easy to test a *joint with a meat thermometer after cooking to ensure it has reached the correct temperature for the type of meat you're cooking (*and you can use an 'ordinary' cooking thermometer for a stew).

I've read of far more 'bad'/unsafe practices from people using a slow cooker - not many people seem to pre-heat the pot for 15 minutes and then cook using the high setting for the first half hour or so. I've also come across people who even cook from frozen in a slow cooker - literally just dump a load of frozen veg, frozen meat (diced chicken or beef are classics) and set the slow cooker to cook on low - that will never reach a food safe temperature quickly enough.

[GillyBee]

I have successfully cooked a boneless turkey roast weighing just over a kilo in a thermal cooker. I put it into a roasting bag and surrounded it with boiling water. It got 30 mins simmering rather than 15mins to ensure good heat transfer and I used a meat thermometer to check it had cooked through OK before serving.
I have a ham in the fridge at the moment. It is a toss up whether I pressure cook it or thermal cook it. If I thermal cook it I will report back.

[GadgetGal]

I have successfully cooked a boneless turkey roast weighing just over a kilo in a thermal cooker. I put it into a roasting bag and surrounded it with boiling water. It got 30 mins simmering rather than 15mins to ensure good heat transfer and I used a meat thermometer to check it had cooked through OK before serving.
I have a ham in the fridge at the moment. It is a toss up whether I pressure cook it or thermal cook it. If I thermal cook it I will report back.

That's really good to hear - I will be interested to hear how your gammon/ham turns out if you do it in your thermal cooker. There's a gammon/ham recipe on the Mr D website if you look at this link: https://mrdscookware.com/recipe/perfect ... glazed-ham.

[rik_uk3]

I've used haybox/pressure/slow cookers for years, use them all now but don't get into a panic about cost, do your homework.

1 Unit of electricity rounded up is 30p
My kettle is 3kw so 3 units per hour turned on and running =90p per hour

500ml cold water to boil 1 minute, so cost of your brew 1.5p

Electric showers are often 10kw so £3 per hour running = 5p per minute, you 5min shower will set you back 25p, four in the family works out at £1 day so cut your shower back to under two mins

Power is expensive but put it into perspective

[GillyBee]

1 Unit of electricity rounded up is 30p
My kettle is 3kw so 3 units per hour turned on and running =90p per hour

500ml cold water to boil 1 minute, so cost of your brew 1.5p

Which is why my 1Kw microwave is a cheaper way to cook some things than the hob.

e.g Frozen beans with a tablespoon of water = 3 minutes on the microwave. On the hob I need to add more water to prevent burning and it takes longer. Christmas pud and "steamed puddings" are also microwave wins taking under 5 minutes instead of an hour or more simmering on the hob as the sugar & fat heat very quickly in a microwave.

[jennyjj01]

I've used haybox/pressure/slow cookers for years, use them all now but don't get into a panic about cost, do your homework.

Power is expensive but put it into perspective

Indeed.
A good comparison might be HayBox or slow cooker for six hours compared to electric oven for one.