This blog documents my journey into low temperature baking (LTB), which is gentle baking at temperatures below 300°F/150°C (mostly below 250°F/121°C), cooking times up to several hours and occasionally days. Low temperature baking includes slow baking, steaming, and dehydration or "warm air baking", the main use of heat in raw foods cuisine. Technically, steaming and dehydration aren't baking, but if they are producing bakery-style goods, then on VaporBaker, they are forms of baking.
LTB can offer better flavor, eveness of cooking, different textures and a healthier composition compared to the furnace heat of conventional ovens. LTB benefits the environment because of lower energy consumption. LTB appliances themselves are very energy efficient. According to Planet Green, slow cookers, for example, are 3 times more energy efficient than toaster ovens (never mind the huge wall ovens in homes), AFTER taking into account the longer operating times of a cooker.
This article only broadly describes LTB methods and techniques. The blog itself is a compendium of my LTB recipes, baking tips and techniques and equipment. Because the recipes are culinary experiments, the ingredient quantities may sometimes barely serve one, though if desired, they could be doubled or tripled to serve more.
There's been renewed interest in low temperature cooking techniques, such as steaming and its haute cuisine cousin sous vide for entree and main course dishes, but not as much for bakery and dessert type goods. Steam baking has been in existence since the discovery of boiling water. Today, it is widespread, if not the favored form of baking. The English have their steamed sweet and savory puddings (which, to Americans, are really steamed cakes and pies), the Asian cuisines have their steamed buns and other snacks, the Americans have their steamed quickbreads like Boston brown bread.
Slow baking is less common. In old times, bread could be baked in a dutch oven buried in the ground and surrounded by lumps of hot coal. That setup can be replicated by a slow cooker on the kitchen countertop or by an oven set at low temperatures. Standard slow cooker baking, however, is not necessarily LTB, because a slow cooker can get much hotter than 300°F over time. Slow cookers also bake inconsistently, because heat power varies from model to model. If its internal temperature can be monitored and held down, a slow cooker can be an excellent LTB appliance.
While raw foodies every now and then do steam and boil foods briefly, warm air baking in a dehydrator is the preferred form of "cooking" to preserve nutrients. Raw foods cakes and breads are mixtures of ground nuts, grains and fruits, shaped into loaves and disks or poured onto trays, and dried at temperatures around 105-115°F/40-46°C. This very low temperature range preserves natural enzymes in food. Raw foods chefs are brilliantly inventive, on the one hand trying to mimic the taste and texture of cooked foods, on the other hand innovating with creations unique to their cuisine.
The dehydration recipes on VaporBaker will not necessarily contain 100% raw ingredients and dehydrator temperatures may go higher than recommended by raw guidelines (food can dry at temperatures up to 140°F/60°C) . Where possible, I will suggest a raw equivalent. Warm air baking is a worthwhile technique outside the raw foods and food preservation context. There's more to it than beef jerky and fruit roll-ups.
My cardinal rule for VaporBaker LTB is temperatures should not exceed 300°F and preferably not higher than 250°F, the point at which toxic compounds (like trans-fatty acids, acrylamides and advanced glycation end products or AGEs) begin forming.1 Controversy rages as to whether these compounds pose a significant threat to human health, but the goal of avoiding them helps to set the upper range of LTB temperatures.
It's possible to bake with exacting heat these days. All dehydrator models (except entry level) have a thermostat. Steam baking (dry and wet) is inherently precision, because water always boils (at sea level) at 212°F. LTB ovens (such as an electronic countertop oven or a slow cooker with temperature control) can output precise heat if they have a thermostat. However, it's always a good idea to monitor oven and food temperatures with cooking thermometers.
Despite all this talk of precision, I try not to obsess over baking temperatures except when testing recipes. For general baking, so long as the numbers remain within guidelines, I let the food cook until it's done, raising or lowering the heat whenever I happen to pass the baking station. Only in a restaurant where customers expect consistency is high precision important. I reach for my trusty instant read thermometer less often than I'd like to admit. The eyes, nose, fingers, a thin wood skewer can be as good a gauge of doneness.
THE EQUIPMENT
The primary LTB appliances are ovens and slow cookers, steamers and dehydrators. For slow baking, conventional home ovens are less than ideal, because their construction and thermostats aren't designed for LTB. New and affordable products do address the LTB market. There are countertop ovens claiming high temperature accuracy priced at less than $200 US. At the other end, passive solar ovens, heated only by the rays of the sun shining down on them, have no trouble making 250°F, even in the dead of winter. Somewhere in the middle are slow cookers, which are more affordable, more versatile, more reliable (compared to a solar oven), but they aren't "set and forget" appliances Thus, the greater part of this article is about how to bake in a slow cooker.
I have read reviews of cookers that heat up so fast, they boil water within an hour. They are fine for baking if tempered with an external temperature control. For manually adjusted heat, these cookers may run too hot for LTB, because one will be constantly scrambling to turn the heat up or down to maintain a steady temperature. My cookers half full of water and set on HIGH for several hours don't boil water (they may simmer after many hours, but don't boil). When buying cookers, check the display models for power consumption. This number has a "W" at the end (for "Watts") and is found near the AC cord exit on the appliance next to the voltage spec. If the number is too high, it could indicate an fast-heating cooker. On the bottom of my 1.5-quart cooker, it reads 120V @ 120W. On my 5.5-quart cooker, it reads 120V @280W. By comparison, toaster ovens and countertop ovens are rated between 1200W and 2000W.
Slow cookers are cheap. I recommend getting two: a small one and a big one. The small one should be round and is ideal for baking small quantities of food, for turning into a dehydrator and as a heat source for rising bread dough. My 1.5-quart cooker cost me $6 US. The large one could be either round or oval. I like the oval crocks for full-size loaves of bread and small cakes. My 5-quart round will hold an 8-inch cake pan with room to spare for a thermometer. A large cooker can bake larger quantities of food, not only because the crock is larger, but also because the heating element is more powerful. The large ones aren't expensive either. A basic 6-quart model can cost as little as $25 US (my 5.5-quart cooker with digital timer was $26 on sale and my standard 5-quart cost just $20). Don't be swayed by fancy controls and features.
Speaking of fancy controls, basic slow cookers (the kind with single-knob heat selector) can be upgraded with an add-on temperature control, the same kind of accessory sold for home sous-vide setups. For LTB, a temperature control is optional, but very helpful. One of my large cookers cannot accept a temperature control, and baking with it is an exercise in patience and vigilance to keep the temperature steady.
Slow cooker temperature controls range in price from as little as $10 for a DIY solution to as much as $200. The simplest controls are repurposed lamp dimmers. The gray box in the picture above is an example of a homemade control. See the link above for more information about how temperature controls work and how to choose one. A temperature control is not a requirement for LTB, but it will make life easier. Again, to anyone who plans to bake a lot in a slow cooker, I STRONGLY recommend adding a temperature control.
High-tech steam ovens (which can cost several times more than a convection oven) cook food the same way as a stovetop steamer - with boiling water. Stainless steel steamers with the width to accommodate full-size cake pans are higher-end or specialty items these days, but my hefty, 9.5-inch inside diameter, 3-piece stovetop steamer set was just $25 on closeout. Two-tier bamboo steamers up to 14" in diameter sell for less than $20 (put these over a saucepan of boiling water - no wok needed). My 7.5-inch stainless steel steamer insert cost me $4 US at a close out store, and fit perfectly in a 2.5-quart saucepot I already owned (the lid fit the steamer too). This smaller insert has the height to hold my 4.5-inch tall bundt pan with room to spare.
Dehydrators (or warm air ovens) are still considered esoteric. General home goods stores stock one or two basic models for around $20-$40 US, but the cheaper ones don't have thermostats. I've seen plans for homemade dehydrators powered by the sun, a room heater, terrarium heater or hair dryer. A slow cooker with a temperature control dries food better than most entry-level dehydrators and can be converted into a multi-tiered dehydrator (see Presto Chango: Turn A Slow Cooker Into A Dehydrator). A regular oven with the door propped open a crack is a no-cost solution, if the oven will operate so far down the thermostat.
Most home kitchens already have most of the equipment for LTB. There certainly is expensive LTB gear for those who can afford it, such as precision countertop ovens, standalone steam ovens, add-on slow cooker thermostats and cookers with temperature dials (an electric roaster is like a slow cooker with an oven thermostat), but a modest investment is all it takes to get started.
Thermometers: Thermometers are essential for checking food and oven temperatures. Slow cookers don't even have thermostats, so I have to monitor cooker temperatures with an analog (dial) oven thermometer or a digital remote probe thermometer. Don't allow them to touch the bottom and walls of the crock, which are hotter than the air inside the crock and will give misleading readings. Put an analog oven thermometer on a trivet (see picture below) or make a stand for it from craft wire. Similarly, a temperature probe should be protected by a wire coil sheath that dissipates heat buildup.
For other situations, I use analog and digital instant-read thermometers. Discount home goods stores sell analog (dial) ones for as little as $6, but the costlier digital thermometers have the advantage of faster and more accurate read times. One of my digitals has a large display, which is easier to read but more cumbersome to hold. The smaller one stabilizes faster.
Test the accuracy of a new thermometer and account for any discrepancies in use. The first way to test it is by dipping it in boiling water, IF the boiling point of water at that location is known. At sea level, water boils at 212°F/100°C, but at higher elevations, water boils at lower temperatures. If the boiling point of water at a specific location is not known, research it online.
The other way to test a thermometer is to dip it in ice water. It should read 32°F/0°C. Not all thermometers read down the the freezing point of water. My candy thermometer doesn't go that low.
Note 1: instant-read thermometers have a probe for inserting into food. The heat sensor in the probe must contact the food to get an accurate reading. In an analog thermometer, the sensor is about 1.5 inches up from the tip of the probe. In a digital thermometer, the sensor is at or very near the tip of the probe, and is more appropriate for testing low-rise cakes and cookies.
Note 2: if the thermometer has a slow response, pre-heat the probe by inserting it in the food for a few seconds before turning it on.
BAKING TIPS
Browning: Of the three types of low temperature baking on VaporBaker, only slow-baking in a dry oven can brown food in a reasonable amount of time. From a chemical perspective, browning is the result of Maillard reactions, enzymatic reactions and the caramelization of sugars. Of these, caramelization is the primary source of browning in baking below 250°F/121°C. Fructose, for example, caramelizes at 230°F/120°C, but glucose and maltose do so at over 320°F/160°C. In general, bread browns at 221°F to 239°F (105°C to 115°C)2, and meat browns at around 302°F/150°C. Browning (especially browning from high temperature Maillard reactions), while imparting delicious flavor, can create toxic compounds. Therefore, when food must be browned, it should be very lightly browned and exposed to high temperatures briefly.
Pre-Heating A Slow-Cooker Oven: In many recipes, the slow cooker must be preheated to a target temperature. For a large cooker (like my oval 5.5 quart), monitor the temperature with an oven thermometer. The thermometer should be on a stand or trivet and not touch the crock, which will be hotter than the air inside. Position the oven thermometer so it won't interfere with the placement of the food, but the dial is still visible.
For a small cooker, if a mini thermometer that will fit unobtrusively in the crock isn't available, a digital remote probe thermometer can monitor the cooker temperature. The probe should be protected with a metal coil to dissipate any hot spots and to stop the probe from touching the crock. The lid can hold the probe in place (re-position to balance if necessary). The method creates a gap, because the lid isn't seated. Put a towel around the lid to block the gap and prevent the hot air from escaping.
Once the thermometer is positioned, put the lid on and cover it with some kitchen towels or a slow cooker draft stop to block heat loss. If the cooker has an external temperature control, follow the control's instructions for pre-heating. Otherwise, turn the cooker to HIGH and heat until it reaches the target temperature. Then turn down to WARM or LOW to steady the temperature.
An empty slow cooker can take over an hour to reach 250°F/121°C (faster if it is insulated with a draft stop). If the batter or dough must be baked as soon as it's ready, wait until the cooker is near or at pre-heat temperature before preparing the dough or batter.
Adjusting Slow Cooker Temperature: If the cooker has an external temperature control, follow the control's instructions for maintaining temperature.
Slow cookers heat up slowly, so check the temperature periodically by reading an in-place oven thermometer or a digital thermometer with a remote probe installed inside the cooker. (Be sure the keep the thermometer or probe away from the bottom and sides of the crock to get the most accurate readings.) To read an analog oven thermometer when there are moisture-absorbing paper towels under the cooker's lid, cut or tear a small hole in the towels so the thermometer will be visible through the glass lid (see picture above). If the hole extends under the lid itself and allows heat to escape, put a kitchen towel around the lid to block the gap.
The average slow cooker (without a fine temperature control) only has 3 settings: WARM, LOW and HIGH. Once the cooker attains a target temperature, shift back and forth among these settings to steady the temperature. If the temperature is too high and there is no lower setting, either turn off the cooker or position the lid askew to vent heat or both. When the temperature has fallen below the target temperature, turn the cooker back on and/or re-seat the lid.
Whatever the oven temperature is maintained manually or automatically, VaporBaker's choice baking temperature for LTB is 250°F/121°C and a maximum of 300°F/150°C. If the cooker should go above 250°F, the food isn't necessarily damaged, because chances are good that it took a while to go that high and the food hasn't been exposed to the highest temperatures for all that time. Simply reduce the temperature and continue baking.
No-Thermometer Baking: If there is no thermometer available or it is too inconvenient to track the temperature, then watch the browning on the bread or pastries. Most breads and pastries begin browning below 250°F/121°C, so if the surface is just starting to brown, then the surface temperature may not have exceeded 250°F/121°C yet. If the surface gets too brown, food temperature may be past 250°F and the inside may be overbaked. Slow-baking without a thermometer is risky, but feasible.
Slow Cooker Oven Capacity: While some steamer inserts and dehydrator trays can be stacked to expand capacity, standalone ovens and slow cookers have fixed capacity. Ovens come with racks that increase the effective capacity. Slow cookers don't usually come with racks, but they can be made from craft wire.
The picture above shows baking racks made from 16-gauge brass wire (sold in craft stores) to support a second pan over the first or to serve as trivets (if the pans loaded with food aren't too heavy). I shaped the wire with a mini needle-nose pliers. The wire ends are "taped" with a strip of aluminum foil and crimped in place.
My small cooker's crock is only 5 inches in diameter and has room for a single mini pan on the bottom. The picture above shows how a baking rack can expand the capacity. It sits in the small cooker, holding a second cake pan over the first. The triangular rack works well with my 4-inch round tart pans. I crafted rectangular racks with adjustable tines to support a range of odd size pans.
Note: The heat is more concentrated at the bottom of the cooker than the top. I wrapped the bottom pan in a collar of aluminum foil so that the cake would bake evenly with the upper cake.
The wire racks also function as a pan support in my 5.5-quart cooker. The crock in the large cooker above has sloping sides. An 8-inch cake pan (for full-size cakes and flat-breads) will fit only halfway down the crock. The wire stand provides a stable platform for the pan and holds it away from the bottom and sides of the crock. (Very heavy pans though would buckle a wire stand. Then, I recommend a small heatproof baking cup or bowl as a support.)
Caution: stacking too many foods can overload a slow cooker so that it doesn't reach the desired temperature or takes a long time to reach that temperature.
Trivets: When baking in a cooker, a pan should not sit on the bottom of the crock, which can get so hot that it scorches foods. Lay a pan rest or trivet made by rolling aluminum foil into a "Z" or zig-zag or wavy shape on the bottom of the cooker first.
To level the trivet, place a pan on top and gently press down to correct any sloping. I recommend rolling foil trivets that span the bottom of the crock for easier placement of pans.
When stacking pans, the bottom pan is likely to bake slightly faster than the top pan, because it's closer to the heat source. Wrapping the lower pan with an aluminum foil collar can slow the baking. My experience has been that the overbaking is slight, and I usually don't bother a collar.
Dry Steaming vs. Wet Steaming: In dry steaming, the steam never touches the food. Instead, the steam only heats the vessel containing the food. For example, the top part of a double boiler holds the food and is heated by the steam from, or direct contact with, the hot water simmering in the saucepan underneath, but a double boiler makes a poor dry steamer because the steam only heats the bottom of the food pot.
Between dry and wet steaming, wet steaming cooks faster and leavened foods tend to rise higher. Some batters don't form properly under wet steam. In the picture above, both cakes from the same batter were steamed for 10 minutes. The cake on the left was dry steamed, and the one on the right was wet steamed. The wet-steamed cake shriveled up, because it absorbed moisture, which collapsed the cake's structure. If a recipe requires a long steaming time, dry steaming can help prevent sogginess. These are generalities, and recipes may use either method under various conditions.
To dry steam cakes and breads in a steamer or water bath, the cake or bread pan is sealed to block out the cooking steam. Any heatproof pan with a tight lid will work. If the pan doesn't have a lid, cover the top with aluminum foil and secure it with a string before setting it in the steamer. Small pans or rubber molds can be enclosed in a foil pouch formed with room for the food to expand.
In wet steaming, the cooking steam touches the food. A simple steamer can be made by putting a heatproof colander on top of a saucepan of boiling water. It works best if the colander doesn't leak steam from the sides. Bamboo steamers are made for wet steaming, although they can dry steam if the food is covered while steaming. Contrary to some cookbooks, bamboo steamers don't need a wok to hold them; put them over a saucepan of boiling water. Choose a saucepan that closely fits the bottom rim of the steamer.
Water Vapor in a Slow Cooker: Slow cookers are not leak-proof. Steam can escape the crock during baking, but also builds up under the lid and can drip back onto the food. A few layers of paper towels under the cooker's lid will absorb moisture and hold back any condensation that forms on the lid.
1 Burton, Norah, Concern Regarding Acrylamide In Food, March 20, 2010;
Goldberg, T. (et al.) Advanced Glycoxidation End Products In Commonly Consumed Foods, J Am Diet Assoc. 2004 Aug;104(8):1287-91;
Acrylamide In Foods, MedicineNet.com, 2005.
2 Browning, Food-Info.net (Wageningen University, The Netherlands).
Purlis, E., Salvadon, V., Bread Browning Kinetics During Baking, Jrnl of Food Engineering, June 2007.
