how I make ice cream
When I share ice cream with friends, it doesn't take long before someone asks, "so how do you make your ice cream?" The short answer, "uhh, I guess I use a spreadsheet and an ice cream machine", is never satisfying. (no, there's no tossing of ziploc bags back and forth, no you can't just use less sugar, no it's not cheaper than store-bought)
After three years, I've learned a bunch of tips that I wish someone had shared with me when I was just starting. I want to walk through the three days that it takes for me to make a batch, and along the way, motivate the science behind each step as opposed to mandating a "best process" without any explanations. Lastly, this is definitely not a followable recipe. Maybe in the future I'll publish some accessible guides for flavor's I'm really proud of.
A quick disclaimer: This isn't the most accessible process, but I hope it doesn't deter from making homemade ice cream. Learning some basic principles and putting in 30% of the effort will still result in really yummy ice cream.
Jump ahead
Day < 0
Design
An ice cream project starts long before the ice cream machine is plugged in. While it takes a minimum of three calendar days to go from raw ingredients to servable hard-pack ice cream, the planning starts much earlier.
Recipe design and the chemistry of mix composition is a whole 'nother topic, but you will typically wrestle with a fair amount spreadsheeting and math (like solving for linear equations) in search of your platonic ideal pint.
Flavor design and selection will also have a big impact on your base mix. The goal is always to target the best texture without compromising for the integrity of the flavor you want to showcase. This starts with deciding on a high-level base: custard, Philly, non-dairy, other etc., and continues with decisions like whether you should use locust bean gum or lambda carrageenan for a given recipe.
You may have to experiment with flavor integration: Do I need to steep my flavor under heat? Cold steep? Add after curing? During churning? Folded in while packing? We can keep the lessons I've learned about flavor integration to a future post.
Of course, you will also have to budget in the time it takes to go grocery shopping. Subtle flavors really demand high ingredient quality. Since you're taking on this labor of love already, I don't think it's worth going for milk or any other ingredient that you wouldn't enjoy consuming on its own.
Day 1
Mix
Pretty self explanatory, but we begin by combining the base ingredients together.
In many ways, ice cream making is more like applied chemistry than cooking, and lack of precision in measurement can have dire consequences. For example, a common benchmark for the amount of stabilizer in a mix is 0.2%-- that's about a gram per pint of mix, and even a half gram deviation could make your ice cream too gummy. When you're investing three+ days and quality ingredients, don't waste your effort by half-assing it. Measure everything by mass to a decent amount of precision. (Trust your gut on how precise, you're allowed be a couple grams off on a 600g cream pour)
Depending on the recipe/flavor you might opt to mix by hand or use a blender, but there are a few principles to keep in mind.
Powder
Most dry powder ingredients can be mixed together first so they're evenly distributed, but some need to be pre-mixed into a slurry with a small amount of liquid to prevent clumping. If you drop tapioca starch into a large amount of cold liquid, you can look into franchising a bubble tea shop since your mix will inadvertently end up with small tapioca pearl clumps. Treat it in the same way you'd make a corn starch slurry to thicken a stir-fry, but you can use a small amount of milk which will then be subtracted from the total milk mass.
Eggs
Eggs (if used) can be another pain point. It's probably easier to just buy cartons of egg yolk (especially for like commercial batch sizes), but I prefer to just use normal eggs. That means the yolk mass your recipe requires is usually not going to be the exact amount the IRL eggs yield. That's why I generally try to tweak my target total mix mass to match the yolk yield I get on a given day.
A rule of thumb: Medium eggs have about 15g of yolk. That means about three eggs (45g) per pint is reasonable if you're using a conventional 4% egg yolk solids benchmark for frozen custard. Another piece of advice, learn some use cases for egg whites because you'll end up with a lot.
Tools
If you mix using a blender, keep ingredient order in mind (i.e. liquids first). Depending on your mix composition, you should also avoid over-mixing if you're using a high powered blender-- you don't want to end up with whipped cream or overheat your mix.
When transferring liquids between containers, a rubber spatula helps a lot with squeegeeing every last bit.
Hey look, six medium yolks is ~90g like I promised
Heat
Why heat the mix?
There are three drivers for heating the mix: safety, texture, and incorporation.
Don't make poison. Pasteurization is important regardless of whether you use eggs or not, and you want to make sure you're not serving a biohazard to your friends. Holding the mix at temp will destroy and deactivate pathogens and enzymes that you don't want to be around.
Heat improves texture. At certain temperature ranges, milk proteins undergo denaturation. This unfolding of protein has a bunch of positive effects including encouraging a more stable mixture and reducing iciness in the final product.
Many dry ingredients mix better when heated. The obvious example is speeding up the rate of sugar dissolution, but heat is also required for some stabilizers, like tapioca starch, that only begin to gelatinize over 60C.
In short, the literature points towards holding your mix at 72C (162F) for 30 minutes. This range checks all the boxes we need: It's held long enough at a temp that guarantees pasteurization and "good" protein denaturation, and not hot enough to promote "bad" protein denaturation nor cause yolks to curdle into scrambled eggs and develop an undesired sulfuric () aroma.
How should we heat the mix?
If you look around online, most recipes will recommend heating the mix over the stove top, with some more thoughtful sources suggesting using a bain-marie to prevent scorching the mix. In my experience, stovetop heating is too annoying to deal with.
First, it's tedious to maintain a steady temperature: Unless you have a precise temperature controlled induction cooker (like the $1500 ChefSteps Control Freak), you have to fiddle with a thermometer and your heat control, and constantly stir and scrape. On top of that, you still have to account for water loss from evaporation. This requires additional measurements, and either calculating in advance or having to further adjust your mix after heating.
I've found that the answer to all of this is simple, heat the mix in a temperature controlled water bath and seal the mix to ensure there's no water loss or contamination during the chilling and curing steps: Use an immersion cooker (sous vide)!
Cuisson sous vide
After mixing, I transfer my mix into heat-safe sealable glass containers and make sure to use about one container per pint of mix to ensure enough surface area. You can also use more traditional vacuum sealed bags-- I stopped doing this because I kept running into leakage problems with crappy quality freezer bags (my problem I know). I think with high quality bags, you might even get a better result since you can more easily massage/mix during the cook if needed. This is especially useful for flavor ingredients that don't hold well in solution. The bags also conduct much better during both the heat and chill steps.
Regardless of which method you choose, if you heat sous vide, start the water at room temperature so you have a better idea of when the mix reaches the target temp; keep the bag/container away from the circulator, walls, and base of the basin; and every once in a while shake up the mix to make sure internal heat is evenly distributed.
Other than these points, heating sous vide makes this step pretty brain dead. Just transfer, seal, and then hit the start button on the cooker. Once the cooker hits 72C, let the mix hold temp for half an hour.
Containerized and warming
Chill
After your mix is done holding at temp, you'll want to chill it to below 5C (40F) as quickly as possible to get it out of the danger zone where bacteria can start to run wild. Even if you're working with a fully sealed pasteurized mix, it's probably still a good idea to be hasty with this step.
All the usual tricks work here, a salted ice water bath plus occasional agitation would be my suggestion. Once it's cool enough for the fridge, move it in. It doesn't hurt to transfer your whole ice bath over if you have the space. (Goes without saying, but do not put hot stuff into your fridge)
Cure
After all this work, you might be inclined to churn your ice cream right away-- this would be a mistake. Without going too deep into the science, aging your mix in the fridge causes fat to crystallize. This encourages a stronger emulsion which results in a smoother, less icy texture. For more reading, the industry buzzword that you'll see around is the partial coalescence of fat crystals.
That concludes day one of work. Let the mix cure overnight (minimum five hours), and rest up-- there's plenty more work to do.
Day 2
Churn
It's time to get to the most exciting part of the process, transforming your hard work into ice cream.
Although the popularity of Pacojet-like (Ninja Creami etc.) ice cream makers are becoming more popular, I'm going to focus on traditionally churned ice cream machines (since that's what I use). Compressor machines with self-contained refrigeration are the ideal option, but our small NYC apartment can only sanely fit a frozen canister machine. I've used the same machine since I started, the two-quart Cuisinart ICE-70. The downside of non-compressor machines is that they require at least three days of pre-freezing to fully chill the canister, and that only one batch can be made at a time per canister. (Do not try to immediately make a second batch without another 2+ day pre-freeze)
The science of churning
Before diving into methodology, it helps to understand why we churn. Also referred to as dynamic freezing in the literature, the goal here is to freeze the water in the mix while minimizing ice crystal size. All churning machine types operate by allowing the mix to freeze in a thin layer on the very cold surface of the chamber, and then immediately scraping the frozen mix off of the walls with what's called a dasher. The crystallized mass is then incorporated into the relatively warmer mix. Ice crystal size directly correlates with the perception of smooth or icy texture, therefore the goal is to operate the machine in a way that prevents the formation of large crystals and prevents the growth of larger crystals. In short, churning is how you end up with ice cream and not a blunt trauma weapon.
Machine settings vary, but the main thing to consider is how fast the ice cream maker rotates. Some machines will lie by labeling settings as "Gelato" or "Ice Cream", but the only difference in these buttons is the variation in RPM. Higher RPMs will whip more air into the ice cream which results in a lighter and airier product, but biting into a high overrun product will immediately remind you of cheap big tub ice cream brands like Edy's or Dreyer's (no shade intended). I adore a dense and chewable ice cream, so I will always go for the slower setting (~50RPM) that results in a lower overrun (think Häagen-Dazs density).
Get active
It's important to note that there is no shortage of active work that you can do during this step 🙂.
Before you start to churn, consider hitting your mix with an immersion blender. This helps homogenize the mixture especially if you're working on a flavor that tend to fall out of suspension. Be wary of introducing heat, and if needed, throw the containers back into the fridge for a bit before you pour it all into the machine.
To begin, most machines are not that great at scraping the nucleated mix from the sides of the chamber (we don't all have a Lello Musso). You'll find that design flaws, engineering tolerance, and the soft plastic will cause a thin frozen layer to form and continue to grow. Unintuitively, ice is an insulator, so this barrier will prevent the liquid mix from accessing the colder nucleation sites on the bare chamber surface. For this reason, a known trick is to either use an ergonomic implement (your thumb? a wooden spoon?) to firmly press the dasher into the side of the chamber until the walls scrape cleanly. (Note: this only works in machines where the dasher is stationary and the chamber is the part that rotates)
As shorn ice crystals reincorporate into the mix, they will clump together into masses that roll around or freeze onto the dasher. Be vigilant in breaking these up and making sure they don't stay in the middle of the chamber for long, otherwise your handcrafted tiny ice crystals will melt and reform into larger crystals.
Another vocab word you'll read regarding this stage is residence time, or the duration your mix stays in the machine. The literature suggests that a lower residence times result in smaller ice crystals and reduce recrystallization, so don't forget about your ice cream after you start the machine. This is also the reason why you want your chamber to be as cold as possible. If possible, lower your freezer temp while pre-freezing a frozen canister.
Extract
So far I haven't addressed when you know the ice cream is done churning. Our target is the draw temperature at which the mix has chilled enough to ensure that enough ice crystals have formed. If we haven't achieved enough ice crystal formation at this stage, liquid water will undergo its initial crystallization in the freezer-- this results in much larger ice crystal formation since static freezing doesn't involve any of the shearing from dynamic freezing.
The highest temperature you should consider beginning extraction at is -6C (21F), but research has shown that even colder temperatures of -10C (14F) result in an even smoother product. This is obviously limited by the temperature of your frozen canister or compressor machine, so if your freezer only gets as cold as -7C, no amount of time in the machine will ever get you below that. For frozen canisters, as time passes and the chamber absorbs more energy, your theoretical minimum draw temperature will continue to rise as well.
During the churning step, if you're bored you can take temperature readings and run some back-of-the-napkin-linear-regressions to forecast when your mix will reach the target draw temp. I use an instant read thermometer (Thermapen), but an infrared thermometer works as well. In my machine, for a quart batch, it usually takes around 25-30 minutes.
Time for a skill check
I would like to introduce the most cursed ice cream making KPI: extraction duration. Time spent in the heat of your room temperature kitchen will cause your ice cream to immediately start to melt, and we all know that frozen melted ice cream does not make for a good texture (everyone has tried at one point in their life to resurrect a forgotten pint).
Despite high-quality blogs and recipes consistently warning of the dangers of being slow to transfer gloopy soft serve into containers for the freezer, no one ever shares any practical tips on how not to make this a terrible messy experience.
And now, an interlude of a recollection of my first time.
As you go to pull out the dasher you realize that about an entire cup of ice cream has coalesced onto the plastic.
In a panic you try to scrape the scraper clean with spatulas that are far too unwieldy, so you give up and dump the poor dessert encrusted plastic into the sink. Trying to salvage the remainder of your ice cream, you start to scoop into your little pint container, but you discover that freshly churned ice cream is very very sticky. In the moment, you attempt to improvise a novel double spatula technique to free the scoops into the pint, but this ends up smearing dairy everywhere as it starts to melt.
You also realize that you have left cavernous air pockets in your pint, so you try to tamp the mix down, but this only causes the packed ice cream to stick to your spatula again. By the time you have extracted most of the loose mix, you realize that a solid quarter centimeter of ice cream has frozen to the chamber walls, since the dasher is languishing in your sink instead of scraping.
You carefully try to scrape the walls and realize you are now a Thai rolled ice cream vendor. By the time you toss these residuals into your pint, they're softly floating in an increasingly liquid pool.
Your net yield is a three-quarters full pint of a formless mess and a crime scene of a kitchen counter.
No one needs to go through this learning experience, so I will offer some advice. (maybe it builds character though)
Budget for more ice cream than you intend to pack. At least make as much liquid mix in volume as you intend to yield, overrun should cover residual losses.
A small plastic rice paddle is your best friend. These things are ergonomic, non-conductive, and won't scratch your canister. Wood would work as well. While I will sometimes lay out an arsenal of rubber spatulas and scrapers, I find I never end up reaching for them.
The dasher is annoying to deal with, so just give your best effort and move on. You can usually lift it out of the chamber, give it a few good scrapes, and dump it into a mixing bowl for the rest of the mix to melt into. If you have time at the end, you can try to salvage it by adding any collected melted mix back into the machine and hand scraping it.
If you're packing pints, follow the technique the gelatieri use. Lift up a heaping mass with your paddle and transfer into the pint by inverting your paddle and scraping the flat of the paddle alongside the inner rim of the container. This ensures that the ice cream is stripped off of the paddle, and also will pack down any ice cream that is getting close to the top. I'll try to get a video of me doing this at some point.
Be at peace with an imperfect yield. It is more important to get your ice cream into the freezer as fast as possible. As the confectioner, you get the privilege of drinking melted mix out of your organizational bowls or developing your rolled ice cream skills as you eat any leftovers out of the machine after extraction is done.
(Is this the ice cream equivalent of the chicken oyster??)
Extract and pack
Freeze
If you've gotten to this point, you now have containers of soft serve sitting in your freezer. During this static freezing stage, the ice cream will continue to harden. If you did everything right and extracted at a recommended draw temperature, new ice crystals will not form since you have already seeded countless tiny ice crystals. It'll take at least six hours for your product to fully firm up. I always plan to leave it overnight.
Pat yourself on the back, but keep the apron for all the dishes you've left in your wake.
Day 3
Serve
For scoopable ice cream, you want to let your pint warm up to at least -18C (0F). "Gelato" (loaded term) is typically served at even warmer temperatures greater than -12C (10F). It's up to you to decide how to serve it: I really enjoy dense ice creams so I tend to serve on the cold side, but flavors really come through as the ice cream starts to warm up above freezer temps. I can't say I've ever pulled out the thermometer at this point though, I just go by feel.
If you're a little freaky in the sheets, take notes for every batch you make. How is the initial sweetness? What about how you perceive the sweetness to change over time? Is it too icy? Is it cakey? Gummy? Melts too fast? Too hard to scoop? Does the flavor come through? Is it too eggy? Do you hate how the color turned out? Part of the fun of this for me is working hard towards improving your spreadsheet recipe and learning about all the different ingredients and chemistry that goes into making your dream pint.
Hold an ice cream party and invite tasters, I promise people will jump on the Partiful. You are immediately the coolest friend since you have ice cream to share (and everybody loves ice cream).
Happy tasters
Citations
This has mostly been a braindump, but I plan to go through and add citations to everything.
The best resources I've come across as a try-hard hobbyist include "Ice Cream 7th Edition", by Goff and Hattel, a comprehensive work on all things ice cream science (you can easily find a pdf if you search around), the incredible blogs by Paul of Underbelly and Ruben of Ice Cream Science.