THIS RECIPE WAS UPDATED ON 16th JANUARY 2016
SECTION 1: THE SCIENCE OF ICE CREAM MAKING AND PREPARATION TIPS
1. Freezing the bowl and equipment
For this recipe, I use the Cuisinart ICE 30BC (click here for my review), which comes with a removable bowl that needs to be frozen overnight before it can be used. The following is a list of domestic ice cream machines with in-built compressors that I’ve tried and would also happily recommend:
- Lello Musso Pola 5030 Desert Maker (click here for my review)
- Cuisinart ICE-100 Compressor Ice Cream and Gelato Maker (click here for my review)
- Lello 4080 Musso Lussino (click here for my review)
- Breville BCI600XL Smart Scoop Ice Cream Maker (click here for my review)
TIP#1 – Cling film
For the Cuisinart ICE-30, the day before you start making your ice cream, take the bowl and cover the top with cling film; use an elastic band to help keep it in place. The cling film will help prevent water vapour in your freezer, as well as any ice that may fall in, from freezing to the inside of the bowl. Any water that freezes at the bowl wall will likely be incorporated into the mix during the churning process, with possible implications for texture if a sufficient amount is incorporated.
It’s also important to freeze enough water in some ice trays to make an ice bath. We’ll be using an ice bath to quickly cool the ice cream mix once it’s been heated, minimising the time the mix spends in the ‘danger zone’, between 5 (41) and 65°C (149°F), where bacteria likes to multiply.
TIP#2 – Freezing the container
Take a 1 litre plastic container and the freezer bowl and put them in your freezer overnight. Freezing the plastic container will remove any stored heat. Heat stored in the container causes the ice cream that contacts the side and bottom to melt, resulting in an increase in ice crystal size.
1.1. Ice crystals in ice cream
Ice crystal size is a critical factor in the development of smooth and creamy ice cream (Donhowe et al. 1991). Smooth and creamy ice cream requires the majority of ice crystals to be small, around 10 to 20 µm in size. If many crystals are larger than this, the ice cream will be perceived as being coarse or icy (Drewett & Hartel 2007; Goff & Hartel 2013).
Ice crystal size is determined by the mix composition and by the freezing process, of which there are two stages: 1. the dynamic freezing stage, where the ice cream mix is frozen in an ice cream machine while being agitated to incorporate air, and 2. the static freezing stage, where the partially frozen ice cream is hardened without agitation in a freezer. Ice crystals form only during the dynamic freezing stage and grow during the static freezing stage.
In this recipe, we will be looking at what we can do to promote the development of small ice crystals during the dynamic freezing stage and then preserve these small crystals during the static freezing stage.
2. Setting the freezer temperature
Your freezer’s temperature has a significant effect on residence time and on ice crystal growth.
2.1. Residence time
If you’re using the Cuisinart ICE 30BC, or any other machine that requires you to freeze the bowl before it can be used, your freezer’s temperature will have a considerable effect on residence time. Residence time is the length of time the ice cream mix spends in your ice cream machine during the dynamic freezing stage and has a significant effect on ice crystal size (Russell et al. 1999; Goff & Hartel 2013; Drewett & Hartel 2007; Cook and Hartel 2010). Russell et al. (1999) found that ice creams made with shorter residence times had smaller ice crystals.
Your freezer’s temperature determines the temperature of the freezer bowl when you leave it to freeze overnight. Lower freezer bowl temperatures can lower the bulk temperature of the ice cream faster, reducing residence time and improving the ice crystal size distribution (Russell et al. 1999; Drewett & Hartel 2007).
TIP#3 – Lower your freezer’s temperature
Set your freezer’s temperature as low as it will go, ideally between -23 to -29°C(-9.4 to -20.2°F), to get your freezer bowl as cold as possible. The colder you can get your freezer, the colder it will get the freezer bowl and the shorter the residence time is likely to be. The shorter the residence time, the smaller the ice crystals and the smoother the texture is likely to be.
I’ve found that my freezer’s temperature has a noticeable effect on residence time when I use my Cuisinart ICE 30BC. When I set my freezer to ‘super freeze’, which gets the temperature down to about -27°C (-16.6°F), it takes about 18 minutes to churn an 800g batch of ice cream. When I set it to -18°C (-0.4°F), it takes about 30 minutes to churn the same amount.
2.2. Ice crystal growth
No new ice crystals are formed during the static freezing stage but the existing small crystals grow in size until the temperature decreases to -18°C (-0.4°F), or ideally -25 to -30°C (-13 to -22°F), to halt this growth. If the ice crystals grow too large during the static freezing stage, a corse or icy texture will develop (Arbuckle 1986).
Quick hardening during the static freezing stage limits ice crystal growth (Goff & Hartel 2013). Similarly, Donhowe (1993) showed that faster cooling of ice cream during hardening resulted in smaller mean ice crystal size.
TIP#4 – Promote quick hardening
To promote quick hardening during the static freezing stage, make sure your freezer is as cold as it will go, ideally -25 to -30°C (-13 to -22°F). Place your ice cream at the back of your freezer where it’s coldest. Try and clear some space in your freezer when chilling your ice cream. Putting ice cream in a densely packed freezer will reduce heat transfer, resulting in an increase in freezing time.
3. Setting your fridge temperature
It’s also important that you set your fridge to between 0 and 2°C (32 and 35.6°F) to increase the rate of crystallisation of the fat globules when you age your mix overnight. Crystallisation of fat during the ageing process helps maintain the shape of ice cream when it is served and also helps minimise the rate at which the ice cream melts (Goff & Hartel 2013). If you don’t allow the fat globules sufficient time to crystallise, it is likely that your ice cream will suffer from relatively fast meltdown and less retention of shape.
4. The size of your pan
The size of the pan you use will affect the rate of evaporation and heating time. I use a large pan with a 23cm diameter to achieve a 15% reduction after 25 minutes heating at 72°C (162°F). If your pan is smaller than 23cm, you will likely need to continue heating your mix for a further 5 minutes or so to reach the desired 15% reduction. Let’s have a look at why it’s important that you heat your mix for the full 25 minutes at 72°C (162°F) and achieve at least a 15% reduction. .
5. The importance of heating time and temperature
There are three principal reasons why we will be heating our mix to 72°C (162°F) and holding it there for at least 25 minutes: 1. to pasteurise the mix, 2. to improve foaming and emulsification, and 3. to improve body and texture.
If you’re running a business and making ice cream to sell, you need to ensure that you are in compliance with food safety legislation. Here in the U.K, the Dairy Products (Hygiene) Regulations 1995, Schedule 6, part v 1 (a) states:
1. Pasteurised ice-cream shall be obtained by the mixture being heated—
to a temperature of not less than 65.6°C (150.1°F) and retained at that temperature for not less than 30 minutes;
to a temperature of not less than 71.1°C (160°F) and retained at that temperature for not less than 10 minutes; or
to a temperature of not less than 79.4°C (174.9°F) and retained at that temperature for not less than 15 seconds.
Ice cream needs to be pasteurised in order to destroy all pathogens and the enzyme phosphatase that may be harmful to health. This is just as important for those of us making ice cream to sell as it is for the home cook.
5.2. To improve foaming and emulsification
The second reason we’ll be heating our mix to 72°C and holding it there for 25 minutes is to improve whey protein foaming and emulsification. Foam formation and its stability is important for texture and for the retention of air that is incorporated into the ice cream during the dynamic freezing stage. Heating milk so that the whey proteins undergo partial protein unfolding yields a more voluminous and more stable foam and improves the emulsifying characteristics of milk protein (Philips et al., 1990). At high temperatures, however, foaming and emulsifying characteristics may be impaired due to protein aggregation (phillips et al., 1990).
At what temperatures, then, do the whey proteins found in milk start to undergo beneficial partial protein unfolding and at what temperatures do they start to aggregate? Sava et al. (2005) held that thermal denaturation of whey protein involves 2 steps: an unfolding step at 70 to 75°C (158 to 167°F), and an aggregation step at 78 to 82.5°C (172.4 to 180.5°F), that mostly follows unfolding.
TIP#5 – 72°C (162°F) for 25 minutes
I’ve found that when I hold my mix at temperatures above 72°C (162°F) for a prolonged period of time, the unpleasant ‘eggy’ hydrogen sulphide taste begins to form and becomes noticeable on eating. I would therefore recommend heating your ice cream mix to 72°C (162°F) and holding it at this temperature for 25 minutes as this significantly improves ice cream body and texture. I’ve run several tests where I have kept the temperature constant at 72°C (162°F), as well as the composition, but have varied the heating times. I’ve found that a mix heated for 25 minutes produces smoother and creamier ice cream than compared to mix heated for 5, 10, and 15 minutes at the same temperature.
5.2.1. Surface hydrophobicity
Surface hydrophobicity is also important in determining emulsifying activity (Monahan et al., 1993). Damodaran (1996) held that denatured proteins have better foaming properties, attributed to increased hydrophobicity, and greater interfacial contact. Sava et al (2005) found that surface hydrophobicity increased considerably at temperatures between 70 and 77.5°C (171.5°F) when whey protein was heated for 45 minutes, with greater increases noted after longer heating times.
Functionality of whey protein also depends on its solubility. Heating at a temperature between 70 (158) and 75°C (167°F) results in a minimal loss of solubility. Sava et al. (2005) noted a decrease in solubility of only 10 to 20% compared with the native protein after 45 minutes.
The literature points to an optimal heating temperature for whey protein at somewhere between 70 (158) and 75°C (167°F). In this temperature range, whey proteins undergo reversible unfolding, which improves foaming and emulsification. Holding whey protein at between 70 (158) and 75°C (167°F) for an extended period of time significantly increases surface hydrophobicity with only a minimal loss of solubility, which improves foaming.
5.3. To improve body and texture
The third reason we are going to heat our ice cream mix to 72°C (162°F) and hold it there for 25 minutes is that heating milk also improves body and texture because of the denaturation of proteins and the consequent increase in their water-holding capacity (Goff & Hartel 2013), which contributes to smooth and creamy texture by helping to minimise ice crystal growth.
6. Weigh your pan
Before you start preparing your mix, it’s important to first weigh your pan and record its weight. This is necessary so that you can check the level of reduction after 25 minutes heating.
The starting weight of our mix will be 1000g. After 25 minutes of heating and a 15% reduction, you should have a mix weight of 850g plus the weight of your pan. If your mix weighs more than 850g plus the weight of your pan, put it back on the heat and continue heating.
Here is how to check the level of reduction after heating for 25 minutes:
My 23cm diameter pan weighs 1606g.
1606g pan + 1000g starting mix = 2606g starting weight.
After 25 minutes of heating, my total weight (1606g pan + 850g 15% reduced mix) should be 2456g.
If my total weight after 25 minutes heating is greater than 2456g, I will continue heating until the weight falls to 2456g or less.
7. Why is skimmed milk powder added to ice cream?
The use of skimmed milk powder in commercial ice cream making is usually associated with economy-style ice cream as it is a cost effective way of reducing the more expensive cream whilst maintaining total solids. In homemade ice cream, however, I’ve found that it is essential for the promotion of smooth and creamy texture.
Skimmed milk powder’s primary role in homemade ice cream is to increase the non-fat milk solids (NMS), namely the whey protein. Flores & Goff (1999) demonstrated that milk proteins had a large impact on texture by limiting ice crystal size and enhancing their stability. I’ve not been able to achieve the same smooth and creamy texture in my homemade ice cream after 25 minutes of heating without the addition of skimmed milk powder.
SECTION 2: THE RECIPE
Makes just under 1 quart (1 litre) of ice cream
About 15 minutes
About 30 minutes
Ice cream maker
A zip-lock bag
1 litre plastic container
Full-fat, semi-skimmed, or skimmed Milk
Skimmed milk powder
60g Wholemeal bread crumbs
1 tsp dark rum
1/4 tsp vanilla extract
1. The importance of butterfat
Milkfat contributes significantly to the rich, full, and creamy flavour and to the smooth texture of ice cream (Goff & Hartel 2013). It’s important that you check the fat content of the cream and the milk that you’ll be using in order to calculate your mix.
Above is the spreadsheet I use to calculate my mixes and I’ve included it for you guys to calculate the exact quantities of milk and cream that you will need. Simply enter the cream fat (usually found on the back of the cream carton and around 35% for you guys in the U.S) and milk fat percentages in the two yellow cells at the top of the spreadsheet. This will then give you the quantities of milk, cream, sugar, egg yolks, and skimmed milk powder needed (in grams) in the cells in blue.
You can use full-fat, semi-skimmed, or skimmed milk. Here in the U.K, our double cream and skimmed milk contain around 47.5% and less than 0.5% of fat respectively, which I have entered as the default values. I recommend using organic milk and cream and organic free-range eggs whenever possible. I use organic milk and cream and organic free range eggs for my business and find that I get a much richer flavour from organic milk and cream and a much deeper colour from free range egg yolks.
2. Toasting the bread
Pour the bread crumbs onto a large baking tray, spreading them evenly, and cover with 40g of Demerara sugar. Pre-heat the grill to a medium-to-high heat. Place the baking tray about 10cm from the heating source and begin grilling the bread crumbs making sure that they are regularly turned and mixed to prevent the bread and sugar from burning. Continue grilling until all the bread is nicely and evenly toasted; this takes me around 10 minutes. You will see some of the sugar starting to melt and the crumbs darken. It’s important that you are attentive to prevent the bread and sugar from burning.
Once the bread is evenly toasted, pour the crumbs and sugar into a large pan and heat over a medium-to-high heat whilst constantly stirring. This will melt more of the sugar into the crumbs and impart a smoky and nutty caramel flavour. Once the sugar starts to smoke, continue stirring for another 5 seconds or so and then take off the heat. Continue stirring for another minute or so to prevent the sugar from burning and allow to cool to room temperature.
3. Preparing an ice bath
Before you start preparing your mix, take a large bowl and fill it with enough ice to make an ice bath. Have a large zip-lock freezer bag ready next to the bowl, along with some table salt. We will be using the zip lock bag and water bath to ensure that the mix is cooled as quickly as possible once it has been heated, minimising the time the mix spends in the ‘danger zone’, between 5 (41) and 65°C (149°F), where bacteria likes to multiply. The longer your mix spends in this ‘danger zone’, the more bacteria is likely to multiply, imparting an undesirable taste and smell.
4. Heating the mix
Weigh your pan and record its weight. We will use this weight to check whether we have achieved the desired 15% reduction after 25 minutes of heating.
Once you’ve prepared the ice bath and weighed your pan, add 140g demerara sugar and 46g skimmed milk powder followed by 78g egg yolks. Mix the yolks, sugar and skimmed milk powder to help prevent the yolks from curdling during heating.
Add the cream and milk and spend a good minute or so mixing all the ingredients before you switch on the heat.
Over a medium heat, heat the mixture until the temperature reaches 71°C (160°F), making sure that you are constantly stirring. You’ll risk burning the proteins and curdling the egg yolks if you do not constantly stir the mix.
Once the temperature reaches 71°C (160°F), turn the heat down to medium-low, move your pan slightly off the heat, and continue heating and stirring until the temperature reaches 72°C (162°F). Use your thermometer to keep your mix at 72°C for 25 minutes, adjusting the position of your pan to help regulate the temperature. Remember that it’s important that you keep your mix at 72°C (162°F) for the full 25 minutes to obtain optimum foaming and emulsifying characteristics. A mix heated for less than 25 minutes will not have the same smooth and creamy texture.
5. Cooling the mix
After 25 minutes, take the pan off the heat and weigh it. If the weight is greater than 850g plus the weight of the pan, place it back on the heat and continue heating for another 2-3 minutes or until you get the weight down sufficiently.
Carefully pour the mix into the zip-lock bag followed by 50g of the bread crumbs and seal. Place it in the water bath and pour about a tablespoon of salt onto the ice to lower the temperature and cool the mix faster. Place the remaining bread crumb and sugar mixture in your fridge.
Once the mix has cooled to room temperature, place the zip-lock bag in the fridge and leave overnight to age and to extract the nutty brown bread flavour.
6. Churning the mix
Once you’ve allowed your mix to age overnight, pour it into your machine followed by the dark rum, vanilla extract, and the remaining bread crumbs. These will give the ice cream a nice crunchy texture.
TIP#6 – Leave the compressor running for about 15 minutes
If you’re using the Cuisinart ICE-100, Breville BCI600XL Smart Scoop, Lello Musso Pola 5030, Lello Musso Lussino 4080, or any other machine with an in-built compressor, with the bowl in the machine, switch on the compressor and leave it running for 10-15 minutes before adding the mix. This will ensure that the freezer bowl is as cold as possible when the mix is added, which will contribute to a reduction in residence time.
TIP#7 – Use your thumb to push the dasher against the side of the bowl
If you’re using the Cuisinart ICE 30BC, use your thumb to push the dasher against the side of the bowl as soon as you pour in the mix. This will ensure that the dasher scrapes off the layer of ice that freezes to the side of the bowl. Any ice that is frozen to the side of the bowl will act as an insulator, slowing the release of heat from the ice cream to the bowl and increasing the residence time. Remember that the longer the residence time, the larger the ice crystals will grow and the sandier the texture is likely to be. Goff & Hartel (2013) note that even a very thin layer of ice remaining on the bowl wall can cause a dramatic reduction in heat transfer. The longer you keep the dasher pushed against the bowl wall, the shorter the residence time is likely to be.
Use a spoon to push along any static lumps of ice cream and ensure that the mix is constantly moving whilst in the machine. Static lumps will likely take longer to freeze, giving the ice crystals more time to grow.
Your mix will be ready when it develops a nice dry, stiff texture, and starts forming ribbon-like swirls. When you remove the dasher, your ice cream should stick firmly to it.
The point at which your mix is ready for extraction will vary from 14-45 minutes depending on the machine you use. For the Cuisinart ICE 30BC, your ice cream should be ready at around 30 minutes of churning. For the Cuisinart ICE-100 and the Breville BCI600XL Smart Scoop, this should be after 32 and 33 minutes respectively. For the Lello Musso Pola 5030, your ice cream will be ready after around 14 minutes and the Lello Musso Lussino 4080 after about 16 minutes.
Just before your mix is ready, quickly take the plastic container out of the freezer and have a large and a small spoon ready. It’s important that you empty your ice cream from the freezer bowl and get it into your freezer as quickly as possible. The extraction time, that is the time it takes to remove the ice cream from the machine and get into into your freezer, has a considerable effect on ice crystal size. This is because as you extract your ice cream from the bowl and into a plastic container, it spends time at room temperature. At this relatively warm room temperature, some of the ice melts from the large ice crystals and the crystals that were initially small melt completely. When you then get your ice cream into your freezer for the static freezing stage, the melted ice re-freezes onto the large ice crystals that survived. The result is that the total number of ice crystals is reduced and their size increases, the perfect formula for coarse texture.
TIP#8 – Get your ice cream into your freezer as quickly as possible
Just holding ice cream at relatively warm room temperatures as you’re extracting it from your machine results in an increase in mean ice crystal size and a decrease in the number of ice crystals present (Goff & Hartel 2013). It’s therefore important that you extract the ice cream from the freezer bowl and get it into your freezer as quickly as possible.
8. Static freezing
When you finish churning your ice cream, it will be extracted from your machine at around -5°C (23°F) and will have a consistency very similar to that of soft serve ice cream. Ice cream is usually served in its scoopbable state at around -12°C (10.4°F) and so you will need to get your ice cream into your freezer to harden. Because ice crystals continue to grow until the temperature drops to -18°C (0.4°F), ideally -25 to -30°C (-13 to -22°C), the faster you get your ice cream below these temperatures, the less ice crystal growth will occur.
After about 4 hours, depending on your freezer, the ice cream will have a nice firm scoopable consistency, somewhere around -15°C (5°F), and be ready to serve.
TIP#4 (again) – Promote quick hardening
To promote quick hardening, make sure your freezer is as cold as possible when you freeze your ice cream. Place your ice cream at the back of your freezer where it is coldest. Try and clear some space in your freezer when chilling your ice cream. Putting ice cream in a densely packed freezer will reduce heat transfer, resulting in an increase in freezing time.
9. Serving your ice cream
Serve your ice cream at around -15°C (5°F). If you can wait, allow the ice cream to warm to below -12°C (10.4°F) before eating. As the serving temperature is increased from -14.4 (6.1) to -7.8°C (18°F), flavour and sweetness become more pronounced.
10. Storing your ice cream
At -18°C (-0.4°F), it is recommended that homemade ice cream be kept for about a week. Ice cream can be stored for several weeks at -25°C (-13°F), and several months at -30°C (-22°F) (Goff 2012). Even at these low temperatures, however, ice crystals will eventually start growing in size. The longer you store your ice cream in the freezer, the larger the ice crystals will grow and the sandier the texture is likely to be.
Try to minimise the number of times you take your ice cream out of the freezer as temperature fluctuations especially promote recrystallisation during the storage of the ice cream (Donhowe & Hartel 1996). Goff & Hartel (2013) state that temperature fluctuations may be associated with 1. changes of temperature of storage, 2. heat shocks, where ice cream is left at room temperatures for extended periods of time, and 3. opening and closing of doors in freezers and storage cabinets. Changes of temperature of storage are associated with frost-free home freezers where temperatures can vary quite widely during the frost-free cycle (Ben-Yoseph & Hartel 1998). Heat shocks occur when ice cream is removed from the freezer, thawed before serving, and then the unfinished ice cream returned to the freezer.
TIP#9 – Switch off your frost-free setting
If possible, switch off your frost free setting when storing ice cream to prevent temperature fluctuations, which contribute to ice crystal growth.
I’d love to hear from you if you do give the recipe a try so do get in touch and say hello!
All the best,
If you’ve found this post helpful and would like to say thanks, you can help me write more content by using the links below to order your ice cream goodies from the chaps at amazon. 🙂
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