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Thermal Profiling for Crumb Set


What is Thermal Profiling for Crumb Set?

Thermal Profiling for Crumb Set is the ability to read and analyze the change in temperature within a product while it is in the oven. This procedure is a step in the quality assurance program that helps produce a consistently high quality product.

Performing a thermal profile, and knowing what is happening in the oven, is critical to controlling the quality of the product. Excessive moisture loss results in a dry, crumbly product, experiencing higher staling rates. Inadequate bake out leaves too much moisture in the product, resulting in a gummy product that takes a longer time to cool, and too much moisture that enhances microbial spoilage (image 1).

Bread slices illustrating the time/temperature S-Curve, showing the importance of a thermal profile.

Image 1: Bread slices illustrating the time/temperature S-Curve.2

When the bread or cake enters the oven, the first thing that occurs is heat transfer.1 Through different heat transfer mechanisms of convection, conduction, and radiation, the heat slowly travels through the product, creating a temperature gradient. This temperature gradient between the core of the product and the exterior temperature will have a large difference at the beginning of the bake, progressing to a much less difference, at the end of the bake. This results in the temperature profile S curve (Figure 1).  When compared to the temperature in the oven, the internal temperature of the product should show a progressively smaller Delta-T as the bake cycle progresses.

A thermal profile should also indicate when yeast kill and starch gelatinization happens during a bake cycle.

Function

Thermal profiling provides basic information that can be used by the baker to determine specific baking qualities from the oven. In high-speed settings, continuous ovens (deck or conveyor) have more than four zones of oven control.

For baking bread, these zones are crucial to controlling the yeast kill, starch gelatinization, gluten and enzyme denaturation, and crumb set. Due to the variability of (burner) zones in continuous ovens currently used in the market, it is difficult to discuss the physiochemical changes that happen in these zones. For discussion, we are dividing the bake cycle (Figure 1) into three major sections:

  1. Oven spring. All the zones that affect the oven spring must be manipulated to reach a yeast kill at no longer than 50% of the baking cycle. Yeast kill must be fast to cut the effect of further production of carbon dioxide that provides more oven spring. The faster the yeast kill, the smaller the oven spring. Faster yeast kill will provide the baker a better control of height requirements.
  2. Critical change. Starch gelatinization, protein, and enzyme deactivation happen in this zone, releasing water and getting ready for the crumb to set. This zone is vital to the physiochemical changes happening to the dough. It turns batter into cake and dough into bread.
  3. Crumb set. This section is very important to the texture of the product. The decrease in % time in this section would dry up the crumb. For example, a product reaching 80% of the bake time in this zone will be drier than a product reaching 90% of the bake time in this zone.

These sections can also be used for quality assurance in batch ovens as well.

Method

A thermal profile is achieved by specific thermally resistant instruments. They consist of a programmable electronic data recorder which utilizes thermocouples inserted into the center of dough or batter and travel with the baked goods throughout the oven. These instruments either log to memory or transfer data in real-time for analysis and reporting with a computer program.

Application

Insert the thermocouples into the center of the bread dough and send the product, together with a full oven load, through a baking cycle. Analyze for yeast kill (60oC or 140oF), starch gelatinization 75oC (167oF) and crumb set (93oC or 200oF). For a typical white bun product, their targets should be as follows:

S-Curve Guidance Internal Dough Temperature % of Bake Time
Yeast Kill 60℃/140oF 50%
Gelatinization 75℃/167oF 60%
Crumb set (Arrival) 93℃/200oF 85%
  • Yeast kill – 50% of the bake time.
  • Starch gelatinization – 60% of the bake time.
  • Crumb set (arrival) – 85% of the bake time. Depending on your product, the % time is determined by how moist or firm you want your product to be. For a moister and softer texture, targets could take as long as 90% of the bake time. In contrast, for a drier and firmer texture, targets could reach as low as 75% of the bake time. Typical white bun products usually reach an arrival value of 93oC (200oF) at <85% of the bake time.

References

  1. Zhou, Weibao, and Nantawan Therdthai. “Heat and Mass Transfer during Baking of Sweet Goods.” Food Engineering Aspects of Baking Sweet Goods. Boca Raton: CRC, 2008. 173-90.
  2. Pearce, Ray. “Re: Thermal Profiling” Received by Katie Jones, 24 Jan. 2017.